root/fs/namespace.c

DEFINITIONS

1. set_mhash_entries
2. set_mphash_entries
3. m_hash
4. mp_hash
5. mnt_alloc_id
6. mnt_free_id
7. mnt_alloc_group_id
8. mnt_release_group_id
9. mnt_add_count
10. mnt_get_count
11. alloc_vfsmnt
12. __mnt_is_readonly
13. mnt_inc_writers
14. mnt_dec_writers
15. mnt_get_writers
16. mnt_is_readonly
17. __mnt_want_write
18. mnt_want_write
19. mnt_clone_write
20. __mnt_want_write_file
21. mnt_want_write_file
22. __mnt_drop_write
23. mnt_drop_write
24. __mnt_drop_write_file
25. mnt_drop_write_file
26. mnt_make_readonly
27. __mnt_unmake_readonly
28. sb_prepare_remount_readonly
29. free_vfsmnt
30. delayed_free_vfsmnt
31. __legitimize_mnt
32. legitimize_mnt
33. __lookup_mnt
34. lookup_mnt
35. __is_local_mountpoint
36. lookup_mountpoint
37. get_mountpoint
38. __put_mountpoint
39. put_mountpoint
40. check_mnt
41. touch_mnt_namespace
42. __touch_mnt_namespace
43. unhash_mnt
44. umount_mnt
45. mnt_set_mountpoint
46. __attach_mnt
47. attach_mnt
48. mnt_change_mountpoint
49. commit_tree
50. next_mnt
51. skip_mnt_tree
52. vfs_create_mount
53. fc_mount
54. vfs_kern_mount
55. vfs_submount
56. clone_mnt
57. cleanup_mnt
58. __cleanup_mnt
59. delayed_mntput
60. mntput_no_expire
61. mntput
62. mntget
63. path_is_mountpoint
64. mnt_clone_internal
65. m_start
66. m_next
67. m_stop
68. m_show
69. may_umount_tree
70. may_umount
71. namespace_unlock
72. namespace_lock
73. disconnect_mount
74. umount_tree
75. do_umount_root
76. do_umount
77. __detach_mounts
78. may_mount
79. may_mandlock
80. may_mandlock
81. ksys_umount
82. SYSCALL_DEFINE2
83. SYSCALL_DEFINE1
84. is_mnt_ns_file
85. to_mnt_ns
86. mnt_ns_loop
87. copy_tree
88. collect_mounts
89. dissolve_on_fput
90. drop_collected_mounts
91. clone_private_mount
92. iterate_mounts
93. lock_mnt_tree
94. cleanup_group_ids
95. invent_group_ids
96. count_mounts
97. attach_recursive_mnt
98. lock_mount
99. unlock_mount
100. graft_tree
101. flags_to_propagation_type
102. do_change_type
103. has_locked_children
104. __do_loopback
105. do_loopback
106. open_detached_copy
107. SYSCALL_DEFINE3
108. can_change_locked_flags
109. change_mount_ro_state
110. set_mount_attributes
111. mnt_warn_timestamp_expiry
112. do_reconfigure_mnt
113. do_remount
114. tree_contains_unbindable
115. check_for_nsfs_mounts
116. do_move_mount
117. do_move_mount_old
118. do_add_mount
119. do_new_mount_fc
120. do_new_mount
121. finish_automount
122. mnt_set_expiry
123. mark_mounts_for_expiry
124. select_submounts
125. shrink_submounts
126. exact_copy_from_user
127. copy_mount_options
128. copy_mount_string
129. do_mount
130. inc_mnt_namespaces
131. dec_mnt_namespaces
132. free_mnt_ns
133. alloc_mnt_ns
134. copy_mnt_ns
135. mount_subtree
136. ksys_mount
137. SYSCALL_DEFINE5
138. SYSCALL_DEFINE3
139. SYSCALL_DEFINE5
140. is_path_reachable
141. path_is_under
142. SYSCALL_DEFINE2
143. init_mount_tree
144. mnt_init
145. put_mnt_ns
146. kern_mount
147. kern_unmount
148. our_mnt
149. current_chrooted
150. mnt_already_visible
151. mount_too_revealing
152. mnt_may_suid
153. mntns_get
154. mntns_put
155. mntns_install
156. mntns_owner

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/fs/namespace.c
   4  *
   5  * (C) Copyright Al Viro 2000, 2001
   6  *
   7  * Based on code from fs/super.c, copyright Linus Torvalds and others.
   8  * Heavily rewritten.
   9  */
  10 
  11 #include <linux/syscalls.h>
  12 #include <linux/export.h>
  13 #include <linux/capability.h>
  14 #include <linux/mnt_namespace.h>
  15 #include <linux/user_namespace.h>
  16 #include <linux/namei.h>
  17 #include <linux/security.h>
  18 #include <linux/cred.h>
  19 #include <linux/idr.h>
  20 #include <linux/init.h>         /* init_rootfs */
  21 #include <linux/fs_struct.h>    /* get_fs_root et.al. */
  22 #include <linux/fsnotify.h>     /* fsnotify_vfsmount_delete */
  23 #include <linux/file.h>
  24 #include <linux/uaccess.h>
  25 #include <linux/proc_ns.h>
  26 #include <linux/magic.h>
  27 #include <linux/memblock.h>
  28 #include <linux/task_work.h>
  29 #include <linux/sched/task.h>
  30 #include <uapi/linux/mount.h>
  31 #include <linux/fs_context.h>
  32 #include <linux/shmem_fs.h>
  33 
  34 #include "pnode.h"
  35 #include "internal.h"
  36 
  37 /* Maximum number of mounts in a mount namespace */
  38 unsigned int sysctl_mount_max __read_mostly = 100000;
  39 
  40 static unsigned int m_hash_mask __read_mostly;
  41 static unsigned int m_hash_shift __read_mostly;
  42 static unsigned int mp_hash_mask __read_mostly;
  43 static unsigned int mp_hash_shift __read_mostly;
  44 
  45 static __initdata unsigned long mhash_entries;
  46 static int __init set_mhash_entries(char *str)
  47 {
  48         if (!str)
  49                 return 0;
  50         mhash_entries = simple_strtoul(str, &str, 0);
  51         return 1;
  52 }
  53 __setup("mhash_entries=", set_mhash_entries);
  54 
  55 static __initdata unsigned long mphash_entries;
  56 static int __init set_mphash_entries(char *str)
  57 {
  58         if (!str)
  59                 return 0;
  60         mphash_entries = simple_strtoul(str, &str, 0);
  61         return 1;
  62 }
  63 __setup("mphash_entries=", set_mphash_entries);
  64 
  65 static u64 event;
  66 static DEFINE_IDA(mnt_id_ida);
  67 static DEFINE_IDA(mnt_group_ida);
  68 
  69 static struct hlist_head *mount_hashtable __read_mostly;
  70 static struct hlist_head *mountpoint_hashtable __read_mostly;
  71 static struct kmem_cache *mnt_cache __read_mostly;
  72 static DECLARE_RWSEM(namespace_sem);
  73 static HLIST_HEAD(unmounted);   /* protected by namespace_sem */
  74 static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
  75 
  76 /* /sys/fs */
  77 struct kobject *fs_kobj;
  78 EXPORT_SYMBOL_GPL(fs_kobj);
  79 
  80 /*
  81  * vfsmount lock may be taken for read to prevent changes to the
  82  * vfsmount hash, ie. during mountpoint lookups or walking back
  83  * up the tree.
  84  *
  85  * It should be taken for write in all cases where the vfsmount
  86  * tree or hash is modified or when a vfsmount structure is modified.
  87  */
  88 __cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
  89 
  90 static inline struct hlist_head *m_hash(struct vfsmount *mnt, struct dentry *dentry)
  91 {
  92         unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
  93         tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
  94         tmp = tmp + (tmp >> m_hash_shift);
  95         return &mount_hashtable[tmp & m_hash_mask];
  96 }
  97 
  98 static inline struct hlist_head *mp_hash(struct dentry *dentry)
  99 {
 100         unsigned long tmp = ((unsigned long)dentry / L1_CACHE_BYTES);
 101         tmp = tmp + (tmp >> mp_hash_shift);
 102         return &mountpoint_hashtable[tmp & mp_hash_mask];
 103 }
 104 
 105 static int mnt_alloc_id(struct mount *mnt)
 106 {
 107         int res = ida_alloc(&mnt_id_ida, GFP_KERNEL);
 108 
 109         if (res < 0)
 110                 return res;
 111         mnt->mnt_id = res;
 112         return 0;
 113 }
 114 
 115 static void mnt_free_id(struct mount *mnt)
 116 {
 117         ida_free(&mnt_id_ida, mnt->mnt_id);
 118 }
 119 
 120 /*
 121  * Allocate a new peer group ID
 122  */
 123 static int mnt_alloc_group_id(struct mount *mnt)
 124 {
 125         int res = ida_alloc_min(&mnt_group_ida, 1, GFP_KERNEL);
 126 
 127         if (res < 0)
 128                 return res;
 129         mnt->mnt_group_id = res;
 130         return 0;
 131 }
 132 
 133 /*
 134  * Release a peer group ID
 135  */
 136 void mnt_release_group_id(struct mount *mnt)
 137 {
 138         ida_free(&mnt_group_ida, mnt->mnt_group_id);
 139         mnt->mnt_group_id = 0;
 140 }
 141 
 142 /*
 143  * vfsmount lock must be held for read
 144  */
 145 static inline void mnt_add_count(struct mount *mnt, int n)
 146 {
 147 #ifdef CONFIG_SMP
 148         this_cpu_add(mnt->mnt_pcp->mnt_count, n);
 149 #else
 150         preempt_disable();
 151         mnt->mnt_count += n;
 152         preempt_enable();
 153 #endif
 154 }
 155 
 156 /*
 157  * vfsmount lock must be held for write
 158  */
 159 unsigned int mnt_get_count(struct mount *mnt)
 160 {
 161 #ifdef CONFIG_SMP
 162         unsigned int count = 0;
 163         int cpu;
 164 
 165         for_each_possible_cpu(cpu) {
 166                 count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
 167         }
 168 
 169         return count;
 170 #else
 171         return mnt->mnt_count;
 172 #endif
 173 }
 174 
 175 static struct mount *alloc_vfsmnt(const char *name)
 176 {
 177         struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
 178         if (mnt) {
 179                 int err;
 180 
 181                 err = mnt_alloc_id(mnt);
 182                 if (err)
 183                         goto out_free_cache;
 184 
 185                 if (name) {
 186                         mnt->mnt_devname = kstrdup_const(name, GFP_KERNEL);
 187                         if (!mnt->mnt_devname)
 188                                 goto out_free_id;
 189                 }
 190 
 191 #ifdef CONFIG_SMP
 192                 mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
 193                 if (!mnt->mnt_pcp)
 194                         goto out_free_devname;
 195 
 196                 this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
 197 #else
 198                 mnt->mnt_count = 1;
 199                 mnt->mnt_writers = 0;
 200 #endif
 201 
 202                 INIT_HLIST_NODE(&mnt->mnt_hash);
 203                 INIT_LIST_HEAD(&mnt->mnt_child);
 204                 INIT_LIST_HEAD(&mnt->mnt_mounts);
 205                 INIT_LIST_HEAD(&mnt->mnt_list);
 206                 INIT_LIST_HEAD(&mnt->mnt_expire);
 207                 INIT_LIST_HEAD(&mnt->mnt_share);
 208                 INIT_LIST_HEAD(&mnt->mnt_slave_list);
 209                 INIT_LIST_HEAD(&mnt->mnt_slave);
 210                 INIT_HLIST_NODE(&mnt->mnt_mp_list);
 211                 INIT_LIST_HEAD(&mnt->mnt_umounting);
 212                 INIT_HLIST_HEAD(&mnt->mnt_stuck_children);
 213         }
 214         return mnt;
 215 
 216 #ifdef CONFIG_SMP
 217 out_free_devname:
 218         kfree_const(mnt->mnt_devname);
 219 #endif
 220 out_free_id:
 221         mnt_free_id(mnt);
 222 out_free_cache:
 223         kmem_cache_free(mnt_cache, mnt);
 224         return NULL;
 225 }
 226 
 227 /*
 228  * Most r/o checks on a fs are for operations that take
 229  * discrete amounts of time, like a write() or unlink().
 230  * We must keep track of when those operations start
 231  * (for permission checks) and when they end, so that
 232  * we can determine when writes are able to occur to
 233  * a filesystem.
 234  */
 235 /*
 236  * __mnt_is_readonly: check whether a mount is read-only
 237  * @mnt: the mount to check for its write status
 238  *
 239  * This shouldn't be used directly ouside of the VFS.
 240  * It does not guarantee that the filesystem will stay
 241  * r/w, just that it is right *now*.  This can not and
 242  * should not be used in place of IS_RDONLY(inode).
 243  * mnt_want/drop_write() will _keep_ the filesystem
 244  * r/w.
 245  */
 246 bool __mnt_is_readonly(struct vfsmount *mnt)
 247 {
 248         return (mnt->mnt_flags & MNT_READONLY) || sb_rdonly(mnt->mnt_sb);
 249 }
 250 EXPORT_SYMBOL_GPL(__mnt_is_readonly);
 251 
 252 static inline void mnt_inc_writers(struct mount *mnt)
 253 {
 254 #ifdef CONFIG_SMP
 255         this_cpu_inc(mnt->mnt_pcp->mnt_writers);
 256 #else
 257         mnt->mnt_writers++;
 258 #endif
 259 }
 260 
 261 static inline void mnt_dec_writers(struct mount *mnt)
 262 {
 263 #ifdef CONFIG_SMP
 264         this_cpu_dec(mnt->mnt_pcp->mnt_writers);
 265 #else
 266         mnt->mnt_writers--;
 267 #endif
 268 }
 269 
 270 static unsigned int mnt_get_writers(struct mount *mnt)
 271 {
 272 #ifdef CONFIG_SMP
 273         unsigned int count = 0;
 274         int cpu;
 275 
 276         for_each_possible_cpu(cpu) {
 277                 count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
 278         }
 279 
 280         return count;
 281 #else
 282         return mnt->mnt_writers;
 283 #endif
 284 }
 285 
 286 static int mnt_is_readonly(struct vfsmount *mnt)
 287 {
 288         if (mnt->mnt_sb->s_readonly_remount)
 289                 return 1;
 290         /* Order wrt setting s_flags/s_readonly_remount in do_remount() */
 291         smp_rmb();
 292         return __mnt_is_readonly(mnt);
 293 }
 294 
 295 /*
 296  * Most r/o & frozen checks on a fs are for operations that take discrete
 297  * amounts of time, like a write() or unlink().  We must keep track of when
 298  * those operations start (for permission checks) and when they end, so that we
 299  * can determine when writes are able to occur to a filesystem.
 300  */
 301 /**
 302  * __mnt_want_write - get write access to a mount without freeze protection
 303  * @m: the mount on which to take a write
 304  *
 305  * This tells the low-level filesystem that a write is about to be performed to
 306  * it, and makes sure that writes are allowed (mnt it read-write) before
 307  * returning success. This operation does not protect against filesystem being
 308  * frozen. When the write operation is finished, __mnt_drop_write() must be
 309  * called. This is effectively a refcount.
 310  */
 311 int __mnt_want_write(struct vfsmount *m)
 312 {
 313         struct mount *mnt = real_mount(m);
 314         int ret = 0;
 315 
 316         preempt_disable();
 317         mnt_inc_writers(mnt);
 318         /*
 319          * The store to mnt_inc_writers must be visible before we pass
 320          * MNT_WRITE_HOLD loop below, so that the slowpath can see our
 321          * incremented count after it has set MNT_WRITE_HOLD.
 322          */
 323         smp_mb();
 324         while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
 325                 cpu_relax();
 326         /*
 327          * After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
 328          * be set to match its requirements. So we must not load that until
 329          * MNT_WRITE_HOLD is cleared.
 330          */
 331         smp_rmb();
 332         if (mnt_is_readonly(m)) {
 333                 mnt_dec_writers(mnt);
 334                 ret = -EROFS;
 335         }
 336         preempt_enable();
 337 
 338         return ret;
 339 }
 340 
 341 /**
 342  * mnt_want_write - get write access to a mount
 343  * @m: the mount on which to take a write
 344  *
 345  * This tells the low-level filesystem that a write is about to be performed to
 346  * it, and makes sure that writes are allowed (mount is read-write, filesystem
 347  * is not frozen) before returning success.  When the write operation is
 348  * finished, mnt_drop_write() must be called.  This is effectively a refcount.
 349  */
 350 int mnt_want_write(struct vfsmount *m)
 351 {
 352         int ret;
 353 
 354         sb_start_write(m->mnt_sb);
 355         ret = __mnt_want_write(m);
 356         if (ret)
 357                 sb_end_write(m->mnt_sb);
 358         return ret;
 359 }
 360 EXPORT_SYMBOL_GPL(mnt_want_write);
 361 
 362 /**
 363  * mnt_clone_write - get write access to a mount
 364  * @mnt: the mount on which to take a write
 365  *
 366  * This is effectively like mnt_want_write, except
 367  * it must only be used to take an extra write reference
 368  * on a mountpoint that we already know has a write reference
 369  * on it. This allows some optimisation.
 370  *
 371  * After finished, mnt_drop_write must be called as usual to
 372  * drop the reference.
 373  */
 374 int mnt_clone_write(struct vfsmount *mnt)
 375 {
 376         /* superblock may be r/o */
 377         if (__mnt_is_readonly(mnt))
 378                 return -EROFS;
 379         preempt_disable();
 380         mnt_inc_writers(real_mount(mnt));
 381         preempt_enable();
 382         return 0;
 383 }
 384 EXPORT_SYMBOL_GPL(mnt_clone_write);
 385 
 386 /**
 387  * __mnt_want_write_file - get write access to a file's mount
 388  * @file: the file who's mount on which to take a write
 389  *
 390  * This is like __mnt_want_write, but it takes a file and can
 391  * do some optimisations if the file is open for write already
 392  */
 393 int __mnt_want_write_file(struct file *file)
 394 {
 395         if (!(file->f_mode & FMODE_WRITER))
 396                 return __mnt_want_write(file->f_path.mnt);
 397         else
 398                 return mnt_clone_write(file->f_path.mnt);
 399 }
 400 
 401 /**
 402  * mnt_want_write_file - get write access to a file's mount
 403  * @file: the file who's mount on which to take a write
 404  *
 405  * This is like mnt_want_write, but it takes a file and can
 406  * do some optimisations if the file is open for write already
 407  */
 408 int mnt_want_write_file(struct file *file)
 409 {
 410         int ret;
 411 
 412         sb_start_write(file_inode(file)->i_sb);
 413         ret = __mnt_want_write_file(file);
 414         if (ret)
 415                 sb_end_write(file_inode(file)->i_sb);
 416         return ret;
 417 }
 418 EXPORT_SYMBOL_GPL(mnt_want_write_file);
 419 
 420 /**
 421  * __mnt_drop_write - give up write access to a mount
 422  * @mnt: the mount on which to give up write access
 423  *
 424  * Tells the low-level filesystem that we are done
 425  * performing writes to it.  Must be matched with
 426  * __mnt_want_write() call above.
 427  */
 428 void __mnt_drop_write(struct vfsmount *mnt)
 429 {
 430         preempt_disable();
 431         mnt_dec_writers(real_mount(mnt));
 432         preempt_enable();
 433 }
 434 
 435 /**
 436  * mnt_drop_write - give up write access to a mount
 437  * @mnt: the mount on which to give up write access
 438  *
 439  * Tells the low-level filesystem that we are done performing writes to it and
 440  * also allows filesystem to be frozen again.  Must be matched with
 441  * mnt_want_write() call above.
 442  */
 443 void mnt_drop_write(struct vfsmount *mnt)
 444 {
 445         __mnt_drop_write(mnt);
 446         sb_end_write(mnt->mnt_sb);
 447 }
 448 EXPORT_SYMBOL_GPL(mnt_drop_write);
 449 
 450 void __mnt_drop_write_file(struct file *file)
 451 {
 452         __mnt_drop_write(file->f_path.mnt);
 453 }
 454 
 455 void mnt_drop_write_file(struct file *file)
 456 {
 457         __mnt_drop_write_file(file);
 458         sb_end_write(file_inode(file)->i_sb);
 459 }
 460 EXPORT_SYMBOL(mnt_drop_write_file);
 461 
 462 static int mnt_make_readonly(struct mount *mnt)
 463 {
 464         int ret = 0;
 465 
 466         lock_mount_hash();
 467         mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
 468         /*
 469          * After storing MNT_WRITE_HOLD, we'll read the counters. This store
 470          * should be visible before we do.
 471          */
 472         smp_mb();
 473 
 474         /*
 475          * With writers on hold, if this value is zero, then there are
 476          * definitely no active writers (although held writers may subsequently
 477          * increment the count, they'll have to wait, and decrement it after
 478          * seeing MNT_READONLY).
 479          *
 480          * It is OK to have counter incremented on one CPU and decremented on
 481          * another: the sum will add up correctly. The danger would be when we
 482          * sum up each counter, if we read a counter before it is incremented,
 483          * but then read another CPU's count which it has been subsequently
 484          * decremented from -- we would see more decrements than we should.
 485          * MNT_WRITE_HOLD protects against this scenario, because
 486          * mnt_want_write first increments count, then smp_mb, then spins on
 487          * MNT_WRITE_HOLD, so it can't be decremented by another CPU while
 488          * we're counting up here.
 489          */
 490         if (mnt_get_writers(mnt) > 0)
 491                 ret = -EBUSY;
 492         else
 493                 mnt->mnt.mnt_flags |= MNT_READONLY;
 494         /*
 495          * MNT_READONLY must become visible before ~MNT_WRITE_HOLD, so writers
 496          * that become unheld will see MNT_READONLY.
 497          */
 498         smp_wmb();
 499         mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
 500         unlock_mount_hash();
 501         return ret;
 502 }
 503 
 504 static int __mnt_unmake_readonly(struct mount *mnt)
 505 {
 506         lock_mount_hash();
 507         mnt->mnt.mnt_flags &= ~MNT_READONLY;
 508         unlock_mount_hash();
 509         return 0;
 510 }
 511 
 512 int sb_prepare_remount_readonly(struct super_block *sb)
 513 {
 514         struct mount *mnt;
 515         int err = 0;
 516 
 517         /* Racy optimization.  Recheck the counter under MNT_WRITE_HOLD */
 518         if (atomic_long_read(&sb->s_remove_count))
 519                 return -EBUSY;
 520 
 521         lock_mount_hash();
 522         list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
 523                 if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
 524                         mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
 525                         smp_mb();
 526                         if (mnt_get_writers(mnt) > 0) {
 527                                 err = -EBUSY;
 528                                 break;
 529                         }
 530                 }
 531         }
 532         if (!err && atomic_long_read(&sb->s_remove_count))
 533                 err = -EBUSY;
 534 
 535         if (!err) {
 536                 sb->s_readonly_remount = 1;
 537                 smp_wmb();
 538         }
 539         list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
 540                 if (mnt->mnt.mnt_flags & MNT_WRITE_HOLD)
 541                         mnt->mnt.mnt_flags &= ~MNT_WRITE_HOLD;
 542         }
 543         unlock_mount_hash();
 544 
 545         return err;
 546 }
 547 
 548 static void free_vfsmnt(struct mount *mnt)
 549 {
 550         kfree_const(mnt->mnt_devname);
 551 #ifdef CONFIG_SMP
 552         free_percpu(mnt->mnt_pcp);
 553 #endif
 554         kmem_cache_free(mnt_cache, mnt);
 555 }
 556 
 557 static void delayed_free_vfsmnt(struct rcu_head *head)
 558 {
 559         free_vfsmnt(container_of(head, struct mount, mnt_rcu));
 560 }
 561 
 562 /* call under rcu_read_lock */
 563 int __legitimize_mnt(struct vfsmount *bastard, unsigned seq)
 564 {
 565         struct mount *mnt;
 566         if (read_seqretry(&mount_lock, seq))
 567                 return 1;
 568         if (bastard == NULL)
 569                 return 0;
 570         mnt = real_mount(bastard);
 571         mnt_add_count(mnt, 1);
 572         smp_mb();                       // see mntput_no_expire()
 573         if (likely(!read_seqretry(&mount_lock, seq)))
 574                 return 0;
 575         if (bastard->mnt_flags & MNT_SYNC_UMOUNT) {
 576                 mnt_add_count(mnt, -1);
 577                 return 1;
 578         }
 579         lock_mount_hash();
 580         if (unlikely(bastard->mnt_flags & MNT_DOOMED)) {
 581                 mnt_add_count(mnt, -1);
 582                 unlock_mount_hash();
 583                 return 1;
 584         }
 585         unlock_mount_hash();
 586         /* caller will mntput() */
 587         return -1;
 588 }
 589 
 590 /* call under rcu_read_lock */
 591 bool legitimize_mnt(struct vfsmount *bastard, unsigned seq)
 592 {
 593         int res = __legitimize_mnt(bastard, seq);
 594         if (likely(!res))
 595                 return true;
 596         if (unlikely(res < 0)) {
 597                 rcu_read_unlock();
 598                 mntput(bastard);
 599                 rcu_read_lock();
 600         }
 601         return false;
 602 }
 603 
 604 /*
 605  * find the first mount at @dentry on vfsmount @mnt.
 606  * call under rcu_read_lock()
 607  */
 608 struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
 609 {
 610         struct hlist_head *head = m_hash(mnt, dentry);
 611         struct mount *p;
 612 
 613         hlist_for_each_entry_rcu(p, head, mnt_hash)
 614                 if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
 615                         return p;
 616         return NULL;
 617 }
 618 
 619 /*
 620  * lookup_mnt - Return the first child mount mounted at path
 621  *
 622  * "First" means first mounted chronologically.  If you create the
 623  * following mounts:
 624  *
 625  * mount /dev/sda1 /mnt
 626  * mount /dev/sda2 /mnt
 627  * mount /dev/sda3 /mnt
 628  *
 629  * Then lookup_mnt() on the base /mnt dentry in the root mount will
 630  * return successively the root dentry and vfsmount of /dev/sda1, then
 631  * /dev/sda2, then /dev/sda3, then NULL.
 632  *
 633  * lookup_mnt takes a reference to the found vfsmount.
 634  */
 635 struct vfsmount *lookup_mnt(const struct path *path)
 636 {
 637         struct mount *child_mnt;
 638         struct vfsmount *m;
 639         unsigned seq;
 640 
 641         rcu_read_lock();
 642         do {
 643                 seq = read_seqbegin(&mount_lock);
 644                 child_mnt = __lookup_mnt(path->mnt, path->dentry);
 645                 m = child_mnt ? &child_mnt->mnt : NULL;
 646         } while (!legitimize_mnt(m, seq));
 647         rcu_read_unlock();
 648         return m;
 649 }
 650 
 651 /*
 652  * __is_local_mountpoint - Test to see if dentry is a mountpoint in the
 653  *                         current mount namespace.
 654  *
 655  * The common case is dentries are not mountpoints at all and that
 656  * test is handled inline.  For the slow case when we are actually
 657  * dealing with a mountpoint of some kind, walk through all of the
 658  * mounts in the current mount namespace and test to see if the dentry
 659  * is a mountpoint.
 660  *
 661  * The mount_hashtable is not usable in the context because we
 662  * need to identify all mounts that may be in the current mount
 663  * namespace not just a mount that happens to have some specified
 664  * parent mount.
 665  */
 666 bool __is_local_mountpoint(struct dentry *dentry)
 667 {
 668         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
 669         struct mount *mnt;
 670         bool is_covered = false;
 671 
 672         if (!d_mountpoint(dentry))
 673                 goto out;
 674 
 675         down_read(&namespace_sem);
 676         list_for_each_entry(mnt, &ns->list, mnt_list) {
 677                 is_covered = (mnt->mnt_mountpoint == dentry);
 678                 if (is_covered)
 679                         break;
 680         }
 681         up_read(&namespace_sem);
 682 out:
 683         return is_covered;
 684 }
 685 
 686 static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
 687 {
 688         struct hlist_head *chain = mp_hash(dentry);
 689         struct mountpoint *mp;
 690 
 691         hlist_for_each_entry(mp, chain, m_hash) {
 692                 if (mp->m_dentry == dentry) {
 693                         mp->m_count++;
 694                         return mp;
 695                 }
 696         }
 697         return NULL;
 698 }
 699 
 700 static struct mountpoint *get_mountpoint(struct dentry *dentry)
 701 {
 702         struct mountpoint *mp, *new = NULL;
 703         int ret;
 704 
 705         if (d_mountpoint(dentry)) {
 706                 /* might be worth a WARN_ON() */
 707                 if (d_unlinked(dentry))
 708                         return ERR_PTR(-ENOENT);
 709 mountpoint:
 710                 read_seqlock_excl(&mount_lock);
 711                 mp = lookup_mountpoint(dentry);
 712                 read_sequnlock_excl(&mount_lock);
 713                 if (mp)
 714                         goto done;
 715         }
 716 
 717         if (!new)
 718                 new = kmalloc(sizeof(struct mountpoint), GFP_KERNEL);
 719         if (!new)
 720                 return ERR_PTR(-ENOMEM);
 721 
 722 
 723         /* Exactly one processes may set d_mounted */
 724         ret = d_set_mounted(dentry);
 725 
 726         /* Someone else set d_mounted? */
 727         if (ret == -EBUSY)
 728                 goto mountpoint;
 729 
 730         /* The dentry is not available as a mountpoint? */
 731         mp = ERR_PTR(ret);
 732         if (ret)
 733                 goto done;
 734 
 735         /* Add the new mountpoint to the hash table */
 736         read_seqlock_excl(&mount_lock);
 737         new->m_dentry = dget(dentry);
 738         new->m_count = 1;
 739         hlist_add_head(&new->m_hash, mp_hash(dentry));
 740         INIT_HLIST_HEAD(&new->m_list);
 741         read_sequnlock_excl(&mount_lock);
 742 
 743         mp = new;
 744         new = NULL;
 745 done:
 746         kfree(new);
 747         return mp;
 748 }
 749 
 750 /*
 751  * vfsmount lock must be held.  Additionally, the caller is responsible
 752  * for serializing calls for given disposal list.
 753  */
 754 static void __put_mountpoint(struct mountpoint *mp, struct list_head *list)
 755 {
 756         if (!--mp->m_count) {
 757                 struct dentry *dentry = mp->m_dentry;
 758                 BUG_ON(!hlist_empty(&mp->m_list));
 759                 spin_lock(&dentry->d_lock);
 760                 dentry->d_flags &= ~DCACHE_MOUNTED;
 761                 spin_unlock(&dentry->d_lock);
 762                 dput_to_list(dentry, list);
 763                 hlist_del(&mp->m_hash);
 764                 kfree(mp);
 765         }
 766 }
 767 
 768 /* called with namespace_lock and vfsmount lock */
 769 static void put_mountpoint(struct mountpoint *mp)
 770 {
 771         __put_mountpoint(mp, &ex_mountpoints);
 772 }
 773 
 774 static inline int check_mnt(struct mount *mnt)
 775 {
 776         return mnt->mnt_ns == current->nsproxy->mnt_ns;
 777 }
 778 
 779 /*
 780  * vfsmount lock must be held for write
 781  */
 782 static void touch_mnt_namespace(struct mnt_namespace *ns)
 783 {
 784         if (ns) {
 785                 ns->event = ++event;
 786                 wake_up_interruptible(&ns->poll);
 787         }
 788 }
 789 
 790 /*
 791  * vfsmount lock must be held for write
 792  */
 793 static void __touch_mnt_namespace(struct mnt_namespace *ns)
 794 {
 795         if (ns && ns->event != event) {
 796                 ns->event = event;
 797                 wake_up_interruptible(&ns->poll);
 798         }
 799 }
 800 
 801 /*
 802  * vfsmount lock must be held for write
 803  */
 804 static struct mountpoint *unhash_mnt(struct mount *mnt)
 805 {
 806         struct mountpoint *mp;
 807         mnt->mnt_parent = mnt;
 808         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
 809         list_del_init(&mnt->mnt_child);
 810         hlist_del_init_rcu(&mnt->mnt_hash);
 811         hlist_del_init(&mnt->mnt_mp_list);
 812         mp = mnt->mnt_mp;
 813         mnt->mnt_mp = NULL;
 814         return mp;
 815 }
 816 
 817 /*
 818  * vfsmount lock must be held for write
 819  */
 820 static void umount_mnt(struct mount *mnt)
 821 {
 822         put_mountpoint(unhash_mnt(mnt));
 823 }
 824 
 825 /*
 826  * vfsmount lock must be held for write
 827  */
 828 void mnt_set_mountpoint(struct mount *mnt,
 829                         struct mountpoint *mp,
 830                         struct mount *child_mnt)
 831 {
 832         mp->m_count++;
 833         mnt_add_count(mnt, 1);  /* essentially, that's mntget */
 834         child_mnt->mnt_mountpoint = mp->m_dentry;
 835         child_mnt->mnt_parent = mnt;
 836         child_mnt->mnt_mp = mp;
 837         hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
 838 }
 839 
 840 static void __attach_mnt(struct mount *mnt, struct mount *parent)
 841 {
 842         hlist_add_head_rcu(&mnt->mnt_hash,
 843                            m_hash(&parent->mnt, mnt->mnt_mountpoint));
 844         list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
 845 }
 846 
 847 /*
 848  * vfsmount lock must be held for write
 849  */
 850 static void attach_mnt(struct mount *mnt,
 851                         struct mount *parent,
 852                         struct mountpoint *mp)
 853 {
 854         mnt_set_mountpoint(parent, mp, mnt);
 855         __attach_mnt(mnt, parent);
 856 }
 857 
 858 void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt)
 859 {
 860         struct mountpoint *old_mp = mnt->mnt_mp;
 861         struct mount *old_parent = mnt->mnt_parent;
 862 
 863         list_del_init(&mnt->mnt_child);
 864         hlist_del_init(&mnt->mnt_mp_list);
 865         hlist_del_init_rcu(&mnt->mnt_hash);
 866 
 867         attach_mnt(mnt, parent, mp);
 868 
 869         put_mountpoint(old_mp);
 870         mnt_add_count(old_parent, -1);
 871 }
 872 
 873 /*
 874  * vfsmount lock must be held for write
 875  */
 876 static void commit_tree(struct mount *mnt)
 877 {
 878         struct mount *parent = mnt->mnt_parent;
 879         struct mount *m;
 880         LIST_HEAD(head);
 881         struct mnt_namespace *n = parent->mnt_ns;
 882 
 883         BUG_ON(parent == mnt);
 884 
 885         list_add_tail(&head, &mnt->mnt_list);
 886         list_for_each_entry(m, &head, mnt_list)
 887                 m->mnt_ns = n;
 888 
 889         list_splice(&head, n->list.prev);
 890 
 891         n->mounts += n->pending_mounts;
 892         n->pending_mounts = 0;
 893 
 894         __attach_mnt(mnt, parent);
 895         touch_mnt_namespace(n);
 896 }
 897 
 898 static struct mount *next_mnt(struct mount *p, struct mount *root)
 899 {
 900         struct list_head *next = p->mnt_mounts.next;
 901         if (next == &p->mnt_mounts) {
 902                 while (1) {
 903                         if (p == root)
 904                                 return NULL;
 905                         next = p->mnt_child.next;
 906                         if (next != &p->mnt_parent->mnt_mounts)
 907                                 break;
 908                         p = p->mnt_parent;
 909                 }
 910         }
 911         return list_entry(next, struct mount, mnt_child);
 912 }
 913 
 914 static struct mount *skip_mnt_tree(struct mount *p)
 915 {
 916         struct list_head *prev = p->mnt_mounts.prev;
 917         while (prev != &p->mnt_mounts) {
 918                 p = list_entry(prev, struct mount, mnt_child);
 919                 prev = p->mnt_mounts.prev;
 920         }
 921         return p;
 922 }
 923 
 924 /**
 925  * vfs_create_mount - Create a mount for a configured superblock
 926  * @fc: The configuration context with the superblock attached
 927  *
 928  * Create a mount to an already configured superblock.  If necessary, the
 929  * caller should invoke vfs_get_tree() before calling this.
 930  *
 931  * Note that this does not attach the mount to anything.
 932  */
 933 struct vfsmount *vfs_create_mount(struct fs_context *fc)
 934 {
 935         struct mount *mnt;
 936 
 937         if (!fc->root)
 938                 return ERR_PTR(-EINVAL);
 939 
 940         mnt = alloc_vfsmnt(fc->source ?: "none");
 941         if (!mnt)
 942                 return ERR_PTR(-ENOMEM);
 943 
 944         if (fc->sb_flags & SB_KERNMOUNT)
 945                 mnt->mnt.mnt_flags = MNT_INTERNAL;
 946 
 947         atomic_inc(&fc->root->d_sb->s_active);
 948         mnt->mnt.mnt_sb         = fc->root->d_sb;
 949         mnt->mnt.mnt_root       = dget(fc->root);
 950         mnt->mnt_mountpoint     = mnt->mnt.mnt_root;
 951         mnt->mnt_parent         = mnt;
 952 
 953         lock_mount_hash();
 954         list_add_tail(&mnt->mnt_instance, &mnt->mnt.mnt_sb->s_mounts);
 955         unlock_mount_hash();
 956         return &mnt->mnt;
 957 }
 958 EXPORT_SYMBOL(vfs_create_mount);
 959 
 960 struct vfsmount *fc_mount(struct fs_context *fc)
 961 {
 962         int err = vfs_get_tree(fc);
 963         if (!err) {
 964                 up_write(&fc->root->d_sb->s_umount);
 965                 return vfs_create_mount(fc);
 966         }
 967         return ERR_PTR(err);
 968 }
 969 EXPORT_SYMBOL(fc_mount);
 970 
 971 struct vfsmount *vfs_kern_mount(struct file_system_type *type,
 972                                 int flags, const char *name,
 973                                 void *data)
 974 {
 975         struct fs_context *fc;
 976         struct vfsmount *mnt;
 977         int ret = 0;
 978 
 979         if (!type)
 980                 return ERR_PTR(-EINVAL);
 981 
 982         fc = fs_context_for_mount(type, flags);
 983         if (IS_ERR(fc))
 984                 return ERR_CAST(fc);
 985 
 986         if (name)
 987                 ret = vfs_parse_fs_string(fc, "source",
 988                                           name, strlen(name));
 989         if (!ret)
 990                 ret = parse_monolithic_mount_data(fc, data);
 991         if (!ret)
 992                 mnt = fc_mount(fc);
 993         else
 994                 mnt = ERR_PTR(ret);
 995 
 996         put_fs_context(fc);
 997         return mnt;
 998 }
 999 EXPORT_SYMBOL_GPL(vfs_kern_mount);
1000 
1001 struct vfsmount *
1002 vfs_submount(const struct dentry *mountpoint, struct file_system_type *type,
1003              const char *name, void *data)
1004 {
1005         /* Until it is worked out how to pass the user namespace
1006          * through from the parent mount to the submount don't support
1007          * unprivileged mounts with submounts.
1008          */
1009         if (mountpoint->d_sb->s_user_ns != &init_user_ns)
1010                 return ERR_PTR(-EPERM);
1011 
1012         return vfs_kern_mount(type, SB_SUBMOUNT, name, data);
1013 }
1014 EXPORT_SYMBOL_GPL(vfs_submount);
1015 
1016 static struct mount *clone_mnt(struct mount *old, struct dentry *root,
1017                                         int flag)
1018 {
1019         struct super_block *sb = old->mnt.mnt_sb;
1020         struct mount *mnt;
1021         int err;
1022 
1023         mnt = alloc_vfsmnt(old->mnt_devname);
1024         if (!mnt)
1025                 return ERR_PTR(-ENOMEM);
1026 
1027         if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
1028                 mnt->mnt_group_id = 0; /* not a peer of original */
1029         else
1030                 mnt->mnt_group_id = old->mnt_group_id;
1031 
1032         if ((flag & CL_MAKE_SHARED) && !mnt->mnt_group_id) {
1033                 err = mnt_alloc_group_id(mnt);
1034                 if (err)
1035                         goto out_free;
1036         }
1037 
1038         mnt->mnt.mnt_flags = old->mnt.mnt_flags;
1039         mnt->mnt.mnt_flags &= ~(MNT_WRITE_HOLD|MNT_MARKED|MNT_INTERNAL);
1040 
1041         atomic_inc(&sb->s_active);
1042         mnt->mnt.mnt_sb = sb;
1043         mnt->mnt.mnt_root = dget(root);
1044         mnt->mnt_mountpoint = mnt->mnt.mnt_root;
1045         mnt->mnt_parent = mnt;
1046         lock_mount_hash();
1047         list_add_tail(&mnt->mnt_instance, &sb->s_mounts);
1048         unlock_mount_hash();
1049 
1050         if ((flag & CL_SLAVE) ||
1051             ((flag & CL_SHARED_TO_SLAVE) && IS_MNT_SHARED(old))) {
1052                 list_add(&mnt->mnt_slave, &old->mnt_slave_list);
1053                 mnt->mnt_master = old;
1054                 CLEAR_MNT_SHARED(mnt);
1055         } else if (!(flag & CL_PRIVATE)) {
1056                 if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
1057                         list_add(&mnt->mnt_share, &old->mnt_share);
1058                 if (IS_MNT_SLAVE(old))
1059                         list_add(&mnt->mnt_slave, &old->mnt_slave);
1060                 mnt->mnt_master = old->mnt_master;
1061         } else {
1062                 CLEAR_MNT_SHARED(mnt);
1063         }
1064         if (flag & CL_MAKE_SHARED)
1065                 set_mnt_shared(mnt);
1066 
1067         /* stick the duplicate mount on the same expiry list
1068          * as the original if that was on one */
1069         if (flag & CL_EXPIRE) {
1070                 if (!list_empty(&old->mnt_expire))
1071                         list_add(&mnt->mnt_expire, &old->mnt_expire);
1072         }
1073 
1074         return mnt;
1075 
1076  out_free:
1077         mnt_free_id(mnt);
1078         free_vfsmnt(mnt);
1079         return ERR_PTR(err);
1080 }
1081 
1082 static void cleanup_mnt(struct mount *mnt)
1083 {
1084         struct hlist_node *p;
1085         struct mount *m;
1086         /*
1087          * The warning here probably indicates that somebody messed
1088          * up a mnt_want/drop_write() pair.  If this happens, the
1089          * filesystem was probably unable to make r/w->r/o transitions.
1090          * The locking used to deal with mnt_count decrement provides barriers,
1091          * so mnt_get_writers() below is safe.
1092          */
1093         WARN_ON(mnt_get_writers(mnt));
1094         if (unlikely(mnt->mnt_pins.first))
1095                 mnt_pin_kill(mnt);
1096         hlist_for_each_entry_safe(m, p, &mnt->mnt_stuck_children, mnt_umount) {
1097                 hlist_del(&m->mnt_umount);
1098                 mntput(&m->mnt);
1099         }
1100         fsnotify_vfsmount_delete(&mnt->mnt);
1101         dput(mnt->mnt.mnt_root);
1102         deactivate_super(mnt->mnt.mnt_sb);
1103         mnt_free_id(mnt);
1104         call_rcu(&mnt->mnt_rcu, delayed_free_vfsmnt);
1105 }
1106 
1107 static void __cleanup_mnt(struct rcu_head *head)
1108 {
1109         cleanup_mnt(container_of(head, struct mount, mnt_rcu));
1110 }
1111 
1112 static LLIST_HEAD(delayed_mntput_list);
1113 static void delayed_mntput(struct work_struct *unused)
1114 {
1115         struct llist_node *node = llist_del_all(&delayed_mntput_list);
1116         struct mount *m, *t;
1117 
1118         llist_for_each_entry_safe(m, t, node, mnt_llist)
1119                 cleanup_mnt(m);
1120 }
1121 static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
1122 
1123 static void mntput_no_expire(struct mount *mnt)
1124 {
1125         LIST_HEAD(list);
1126 
1127         rcu_read_lock();
1128         if (likely(READ_ONCE(mnt->mnt_ns))) {
1129                 /*
1130                  * Since we don't do lock_mount_hash() here,
1131                  * ->mnt_ns can change under us.  However, if it's
1132                  * non-NULL, then there's a reference that won't
1133                  * be dropped until after an RCU delay done after
1134                  * turning ->mnt_ns NULL.  So if we observe it
1135                  * non-NULL under rcu_read_lock(), the reference
1136                  * we are dropping is not the final one.
1137                  */
1138                 mnt_add_count(mnt, -1);
1139                 rcu_read_unlock();
1140                 return;
1141         }
1142         lock_mount_hash();
1143         /*
1144          * make sure that if __legitimize_mnt() has not seen us grab
1145          * mount_lock, we'll see their refcount increment here.
1146          */
1147         smp_mb();
1148         mnt_add_count(mnt, -1);
1149         if (mnt_get_count(mnt)) {
1150                 rcu_read_unlock();
1151                 unlock_mount_hash();
1152                 return;
1153         }
1154         if (unlikely(mnt->mnt.mnt_flags & MNT_DOOMED)) {
1155                 rcu_read_unlock();
1156                 unlock_mount_hash();
1157                 return;
1158         }
1159         mnt->mnt.mnt_flags |= MNT_DOOMED;
1160         rcu_read_unlock();
1161 
1162         list_del(&mnt->mnt_instance);
1163 
1164         if (unlikely(!list_empty(&mnt->mnt_mounts))) {
1165                 struct mount *p, *tmp;
1166                 list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts,  mnt_child) {
1167                         __put_mountpoint(unhash_mnt(p), &list);
1168                         hlist_add_head(&p->mnt_umount, &mnt->mnt_stuck_children);
1169                 }
1170         }
1171         unlock_mount_hash();
1172         shrink_dentry_list(&list);
1173 
1174         if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
1175                 struct task_struct *task = current;
1176                 if (likely(!(task->flags & PF_KTHREAD))) {
1177                         init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
1178                         if (!task_work_add(task, &mnt->mnt_rcu, true))
1179                                 return;
1180                 }
1181                 if (llist_add(&mnt->mnt_llist, &delayed_mntput_list))
1182                         schedule_delayed_work(&delayed_mntput_work, 1);
1183                 return;
1184         }
1185         cleanup_mnt(mnt);
1186 }
1187 
1188 void mntput(struct vfsmount *mnt)
1189 {
1190         if (mnt) {
1191                 struct mount *m = real_mount(mnt);
1192                 /* avoid cacheline pingpong, hope gcc doesn't get "smart" */
1193                 if (unlikely(m->mnt_expiry_mark))
1194                         m->mnt_expiry_mark = 0;
1195                 mntput_no_expire(m);
1196         }
1197 }
1198 EXPORT_SYMBOL(mntput);
1199 
1200 struct vfsmount *mntget(struct vfsmount *mnt)
1201 {
1202         if (mnt)
1203                 mnt_add_count(real_mount(mnt), 1);
1204         return mnt;
1205 }
1206 EXPORT_SYMBOL(mntget);
1207 
1208 /* path_is_mountpoint() - Check if path is a mount in the current
1209  *                          namespace.
1210  *
1211  *  d_mountpoint() can only be used reliably to establish if a dentry is
1212  *  not mounted in any namespace and that common case is handled inline.
1213  *  d_mountpoint() isn't aware of the possibility there may be multiple
1214  *  mounts using a given dentry in a different namespace. This function
1215  *  checks if the passed in path is a mountpoint rather than the dentry
1216  *  alone.
1217  */
1218 bool path_is_mountpoint(const struct path *path)
1219 {
1220         unsigned seq;
1221         bool res;
1222 
1223         if (!d_mountpoint(path->dentry))
1224                 return false;
1225 
1226         rcu_read_lock();
1227         do {
1228                 seq = read_seqbegin(&mount_lock);
1229                 res = __path_is_mountpoint(path);
1230         } while (read_seqretry(&mount_lock, seq));
1231         rcu_read_unlock();
1232 
1233         return res;
1234 }
1235 EXPORT_SYMBOL(path_is_mountpoint);
1236 
1237 struct vfsmount *mnt_clone_internal(const struct path *path)
1238 {
1239         struct mount *p;
1240         p = clone_mnt(real_mount(path->mnt), path->dentry, CL_PRIVATE);
1241         if (IS_ERR(p))
1242                 return ERR_CAST(p);
1243         p->mnt.mnt_flags |= MNT_INTERNAL;
1244         return &p->mnt;
1245 }
1246 
1247 #ifdef CONFIG_PROC_FS
1248 /* iterator; we want it to have access to namespace_sem, thus here... */
1249 static void *m_start(struct seq_file *m, loff_t *pos)
1250 {
1251         struct proc_mounts *p = m->private;
1252 
1253         down_read(&namespace_sem);
1254         if (p->cached_event == p->ns->event) {
1255                 void *v = p->cached_mount;
1256                 if (*pos == p->cached_index)
1257                         return v;
1258                 if (*pos == p->cached_index + 1) {
1259                         v = seq_list_next(v, &p->ns->list, &p->cached_index);
1260                         return p->cached_mount = v;
1261                 }
1262         }
1263 
1264         p->cached_event = p->ns->event;
1265         p->cached_mount = seq_list_start(&p->ns->list, *pos);
1266         p->cached_index = *pos;
1267         return p->cached_mount;
1268 }
1269 
1270 static void *m_next(struct seq_file *m, void *v, loff_t *pos)
1271 {
1272         struct proc_mounts *p = m->private;
1273 
1274         p->cached_mount = seq_list_next(v, &p->ns->list, pos);
1275         p->cached_index = *pos;
1276         return p->cached_mount;
1277 }
1278 
1279 static void m_stop(struct seq_file *m, void *v)
1280 {
1281         up_read(&namespace_sem);
1282 }
1283 
1284 static int m_show(struct seq_file *m, void *v)
1285 {
1286         struct proc_mounts *p = m->private;
1287         struct mount *r = list_entry(v, struct mount, mnt_list);
1288         return p->show(m, &r->mnt);
1289 }
1290 
1291 const struct seq_operations mounts_op = {
1292         .start  = m_start,
1293         .next   = m_next,
1294         .stop   = m_stop,
1295         .show   = m_show,
1296 };
1297 #endif  /* CONFIG_PROC_FS */
1298 
1299 /**
1300  * may_umount_tree - check if a mount tree is busy
1301  * @mnt: root of mount tree
1302  *
1303  * This is called to check if a tree of mounts has any
1304  * open files, pwds, chroots or sub mounts that are
1305  * busy.
1306  */
1307 int may_umount_tree(struct vfsmount *m)
1308 {
1309         struct mount *mnt = real_mount(m);
1310         int actual_refs = 0;
1311         int minimum_refs = 0;
1312         struct mount *p;
1313         BUG_ON(!m);
1314 
1315         /* write lock needed for mnt_get_count */
1316         lock_mount_hash();
1317         for (p = mnt; p; p = next_mnt(p, mnt)) {
1318                 actual_refs += mnt_get_count(p);
1319                 minimum_refs += 2;
1320         }
1321         unlock_mount_hash();
1322 
1323         if (actual_refs > minimum_refs)
1324                 return 0;
1325 
1326         return 1;
1327 }
1328 
1329 EXPORT_SYMBOL(may_umount_tree);
1330 
1331 /**
1332  * may_umount - check if a mount point is busy
1333  * @mnt: root of mount
1334  *
1335  * This is called to check if a mount point has any
1336  * open files, pwds, chroots or sub mounts. If the
1337  * mount has sub mounts this will return busy
1338  * regardless of whether the sub mounts are busy.
1339  *
1340  * Doesn't take quota and stuff into account. IOW, in some cases it will
1341  * give false negatives. The main reason why it's here is that we need
1342  * a non-destructive way to look for easily umountable filesystems.
1343  */
1344 int may_umount(struct vfsmount *mnt)
1345 {
1346         int ret = 1;
1347         down_read(&namespace_sem);
1348         lock_mount_hash();
1349         if (propagate_mount_busy(real_mount(mnt), 2))
1350                 ret = 0;
1351         unlock_mount_hash();
1352         up_read(&namespace_sem);
1353         return ret;
1354 }
1355 
1356 EXPORT_SYMBOL(may_umount);
1357 
1358 static void namespace_unlock(void)
1359 {
1360         struct hlist_head head;
1361         struct hlist_node *p;
1362         struct mount *m;
1363         LIST_HEAD(list);
1364 
1365         hlist_move_list(&unmounted, &head);
1366         list_splice_init(&ex_mountpoints, &list);
1367 
1368         up_write(&namespace_sem);
1369 
1370         shrink_dentry_list(&list);
1371 
1372         if (likely(hlist_empty(&head)))
1373                 return;
1374 
1375         synchronize_rcu_expedited();
1376 
1377         hlist_for_each_entry_safe(m, p, &head, mnt_umount) {
1378                 hlist_del(&m->mnt_umount);
1379                 mntput(&m->mnt);
1380         }
1381 }
1382 
1383 static inline void namespace_lock(void)
1384 {
1385         down_write(&namespace_sem);
1386 }
1387 
1388 enum umount_tree_flags {
1389         UMOUNT_SYNC = 1,
1390         UMOUNT_PROPAGATE = 2,
1391         UMOUNT_CONNECTED = 4,
1392 };
1393 
1394 static bool disconnect_mount(struct mount *mnt, enum umount_tree_flags how)
1395 {
1396         /* Leaving mounts connected is only valid for lazy umounts */
1397         if (how & UMOUNT_SYNC)
1398                 return true;
1399 
1400         /* A mount without a parent has nothing to be connected to */
1401         if (!mnt_has_parent(mnt))
1402                 return true;
1403 
1404         /* Because the reference counting rules change when mounts are
1405          * unmounted and connected, umounted mounts may not be
1406          * connected to mounted mounts.
1407          */
1408         if (!(mnt->mnt_parent->mnt.mnt_flags & MNT_UMOUNT))
1409                 return true;
1410 
1411         /* Has it been requested that the mount remain connected? */
1412         if (how & UMOUNT_CONNECTED)
1413                 return false;
1414 
1415         /* Is the mount locked such that it needs to remain connected? */
1416         if (IS_MNT_LOCKED(mnt))
1417                 return false;
1418 
1419         /* By default disconnect the mount */
1420         return true;
1421 }
1422 
1423 /*
1424  * mount_lock must be held
1425  * namespace_sem must be held for write
1426  */
1427 static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
1428 {
1429         LIST_HEAD(tmp_list);
1430         struct mount *p;
1431 
1432         if (how & UMOUNT_PROPAGATE)
1433                 propagate_mount_unlock(mnt);
1434 
1435         /* Gather the mounts to umount */
1436         for (p = mnt; p; p = next_mnt(p, mnt)) {
1437                 p->mnt.mnt_flags |= MNT_UMOUNT;
1438                 list_move(&p->mnt_list, &tmp_list);
1439         }
1440 
1441         /* Hide the mounts from mnt_mounts */
1442         list_for_each_entry(p, &tmp_list, mnt_list) {
1443                 list_del_init(&p->mnt_child);
1444         }
1445 
1446         /* Add propogated mounts to the tmp_list */
1447         if (how & UMOUNT_PROPAGATE)
1448                 propagate_umount(&tmp_list);
1449 
1450         while (!list_empty(&tmp_list)) {
1451                 struct mnt_namespace *ns;
1452                 bool disconnect;
1453                 p = list_first_entry(&tmp_list, struct mount, mnt_list);
1454                 list_del_init(&p->mnt_expire);
1455                 list_del_init(&p->mnt_list);
1456                 ns = p->mnt_ns;
1457                 if (ns) {
1458                         ns->mounts--;
1459                         __touch_mnt_namespace(ns);
1460                 }
1461                 p->mnt_ns = NULL;
1462                 if (how & UMOUNT_SYNC)
1463                         p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
1464 
1465                 disconnect = disconnect_mount(p, how);
1466                 if (mnt_has_parent(p)) {
1467                         mnt_add_count(p->mnt_parent, -1);
1468                         if (!disconnect) {
1469                                 /* Don't forget about p */
1470                                 list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
1471                         } else {
1472                                 umount_mnt(p);
1473                         }
1474                 }
1475                 change_mnt_propagation(p, MS_PRIVATE);
1476                 if (disconnect)
1477                         hlist_add_head(&p->mnt_umount, &unmounted);
1478         }
1479 }
1480 
1481 static void shrink_submounts(struct mount *mnt);
1482 
1483 static int do_umount_root(struct super_block *sb)
1484 {
1485         int ret = 0;
1486 
1487         down_write(&sb->s_umount);
1488         if (!sb_rdonly(sb)) {
1489                 struct fs_context *fc;
1490 
1491                 fc = fs_context_for_reconfigure(sb->s_root, SB_RDONLY,
1492                                                 SB_RDONLY);
1493                 if (IS_ERR(fc)) {
1494                         ret = PTR_ERR(fc);
1495                 } else {
1496                         ret = parse_monolithic_mount_data(fc, NULL);
1497                         if (!ret)
1498                                 ret = reconfigure_super(fc);
1499                         put_fs_context(fc);
1500                 }
1501         }
1502         up_write(&sb->s_umount);
1503         return ret;
1504 }
1505 
1506 static int do_umount(struct mount *mnt, int flags)
1507 {
1508         struct super_block *sb = mnt->mnt.mnt_sb;
1509         int retval;
1510 
1511         retval = security_sb_umount(&mnt->mnt, flags);
1512         if (retval)
1513                 return retval;
1514 
1515         /*
1516          * Allow userspace to request a mountpoint be expired rather than
1517          * unmounting unconditionally. Unmount only happens if:
1518          *  (1) the mark is already set (the mark is cleared by mntput())
1519          *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
1520          */
1521         if (flags & MNT_EXPIRE) {
1522                 if (&mnt->mnt == current->fs->root.mnt ||
1523                     flags & (MNT_FORCE | MNT_DETACH))
1524                         return -EINVAL;
1525 
1526                 /*
1527                  * probably don't strictly need the lock here if we examined
1528                  * all race cases, but it's a slowpath.
1529                  */
1530                 lock_mount_hash();
1531                 if (mnt_get_count(mnt) != 2) {
1532                         unlock_mount_hash();
1533                         return -EBUSY;
1534                 }
1535                 unlock_mount_hash();
1536 
1537                 if (!xchg(&mnt->mnt_expiry_mark, 1))
1538                         return -EAGAIN;
1539         }
1540 
1541         /*
1542          * If we may have to abort operations to get out of this
1543          * mount, and they will themselves hold resources we must
1544          * allow the fs to do things. In the Unix tradition of
1545          * 'Gee thats tricky lets do it in userspace' the umount_begin
1546          * might fail to complete on the first run through as other tasks
1547          * must return, and the like. Thats for the mount program to worry
1548          * about for the moment.
1549          */
1550 
1551         if (flags & MNT_FORCE && sb->s_op->umount_begin) {
1552                 sb->s_op->umount_begin(sb);
1553         }
1554 
1555         /*
1556          * No sense to grab the lock for this test, but test itself looks
1557          * somewhat bogus. Suggestions for better replacement?
1558          * Ho-hum... In principle, we might treat that as umount + switch
1559          * to rootfs. GC would eventually take care of the old vfsmount.
1560          * Actually it makes sense, especially if rootfs would contain a
1561          * /reboot - static binary that would close all descriptors and
1562          * call reboot(9). Then init(8) could umount root and exec /reboot.
1563          */
1564         if (&mnt->mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
1565                 /*
1566                  * Special case for "unmounting" root ...
1567                  * we just try to remount it readonly.
1568                  */
1569                 if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
1570                         return -EPERM;
1571                 return do_umount_root(sb);
1572         }
1573 
1574         namespace_lock();
1575         lock_mount_hash();
1576 
1577         /* Recheck MNT_LOCKED with the locks held */
1578         retval = -EINVAL;
1579         if (mnt->mnt.mnt_flags & MNT_LOCKED)
1580                 goto out;
1581 
1582         event++;
1583         if (flags & MNT_DETACH) {
1584                 if (!list_empty(&mnt->mnt_list))
1585                         umount_tree(mnt, UMOUNT_PROPAGATE);
1586                 retval = 0;
1587         } else {
1588                 shrink_submounts(mnt);
1589                 retval = -EBUSY;
1590                 if (!propagate_mount_busy(mnt, 2)) {
1591                         if (!list_empty(&mnt->mnt_list))
1592                                 umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
1593                         retval = 0;
1594                 }
1595         }
1596 out:
1597         unlock_mount_hash();
1598         namespace_unlock();
1599         return retval;
1600 }
1601 
1602 /*
1603  * __detach_mounts - lazily unmount all mounts on the specified dentry
1604  *
1605  * During unlink, rmdir, and d_drop it is possible to loose the path
1606  * to an existing mountpoint, and wind up leaking the mount.
1607  * detach_mounts allows lazily unmounting those mounts instead of
1608  * leaking them.
1609  *
1610  * The caller may hold dentry->d_inode->i_mutex.
1611  */
1612 void __detach_mounts(struct dentry *dentry)
1613 {
1614         struct mountpoint *mp;
1615         struct mount *mnt;
1616 
1617         namespace_lock();
1618         lock_mount_hash();
1619         mp = lookup_mountpoint(dentry);
1620         if (!mp)
1621                 goto out_unlock;
1622 
1623         event++;
1624         while (!hlist_empty(&mp->m_list)) {
1625                 mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
1626                 if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
1627                         umount_mnt(mnt);
1628                         hlist_add_head(&mnt->mnt_umount, &unmounted);
1629                 }
1630                 else umount_tree(mnt, UMOUNT_CONNECTED);
1631         }
1632         put_mountpoint(mp);
1633 out_unlock:
1634         unlock_mount_hash();
1635         namespace_unlock();
1636 }
1637 
1638 /*
1639  * Is the caller allowed to modify his namespace?
1640  */
1641 static inline bool may_mount(void)
1642 {
1643         return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
1644 }
1645 
1646 #ifdef  CONFIG_MANDATORY_FILE_LOCKING
1647 static inline bool may_mandlock(void)
1648 {
1649         return capable(CAP_SYS_ADMIN);
1650 }
1651 #else
1652 static inline bool may_mandlock(void)
1653 {
1654         pr_warn("VFS: \"mand\" mount option not supported");
1655         return false;
1656 }
1657 #endif
1658 
1659 /*
1660  * Now umount can handle mount points as well as block devices.
1661  * This is important for filesystems which use unnamed block devices.
1662  *
1663  * We now support a flag for forced unmount like the other 'big iron'
1664  * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
1665  */
1666 
1667 int ksys_umount(char __user *name, int flags)
1668 {
1669         struct path path;
1670         struct mount *mnt;
1671         int retval;
1672         int lookup_flags = 0;
1673 
1674         if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
1675                 return -EINVAL;
1676 
1677         if (!may_mount())
1678                 return -EPERM;
1679 
1680         if (!(flags & UMOUNT_NOFOLLOW))
1681                 lookup_flags |= LOOKUP_FOLLOW;
1682 
1683         retval = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);
1684         if (retval)
1685                 goto out;
1686         mnt = real_mount(path.mnt);
1687         retval = -EINVAL;
1688         if (path.dentry != path.mnt->mnt_root)
1689                 goto dput_and_out;
1690         if (!check_mnt(mnt))
1691                 goto dput_and_out;
1692         if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
1693                 goto dput_and_out;
1694         retval = -EPERM;
1695         if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
1696                 goto dput_and_out;
1697 
1698         retval = do_umount(mnt, flags);
1699 dput_and_out:
1700         /* we mustn't call path_put() as that would clear mnt_expiry_mark */
1701         dput(path.dentry);
1702         mntput_no_expire(mnt);
1703 out:
1704         return retval;
1705 }
1706 
1707 SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
1708 {
1709         return ksys_umount(name, flags);
1710 }
1711 
1712 #ifdef __ARCH_WANT_SYS_OLDUMOUNT
1713 
1714 /*
1715  *      The 2.0 compatible umount. No flags.
1716  */
1717 SYSCALL_DEFINE1(oldumount, char __user *, name)
1718 {
1719         return ksys_umount(name, 0);
1720 }
1721 
1722 #endif
1723 
1724 static bool is_mnt_ns_file(struct dentry *dentry)
1725 {
1726         /* Is this a proxy for a mount namespace? */
1727         return dentry->d_op == &ns_dentry_operations &&
1728                dentry->d_fsdata == &mntns_operations;
1729 }
1730 
1731 struct mnt_namespace *to_mnt_ns(struct ns_common *ns)
1732 {
1733         return container_of(ns, struct mnt_namespace, ns);
1734 }
1735 
1736 static bool mnt_ns_loop(struct dentry *dentry)
1737 {
1738         /* Could bind mounting the mount namespace inode cause a
1739          * mount namespace loop?
1740          */
1741         struct mnt_namespace *mnt_ns;
1742         if (!is_mnt_ns_file(dentry))
1743                 return false;
1744 
1745         mnt_ns = to_mnt_ns(get_proc_ns(dentry->d_inode));
1746         return current->nsproxy->mnt_ns->seq >= mnt_ns->seq;
1747 }
1748 
1749 struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
1750                                         int flag)
1751 {
1752         struct mount *res, *p, *q, *r, *parent;
1753 
1754         if (!(flag & CL_COPY_UNBINDABLE) && IS_MNT_UNBINDABLE(mnt))
1755                 return ERR_PTR(-EINVAL);
1756 
1757         if (!(flag & CL_COPY_MNT_NS_FILE) && is_mnt_ns_file(dentry))
1758                 return ERR_PTR(-EINVAL);
1759 
1760         res = q = clone_mnt(mnt, dentry, flag);
1761         if (IS_ERR(q))
1762                 return q;
1763 
1764         q->mnt_mountpoint = mnt->mnt_mountpoint;
1765 
1766         p = mnt;
1767         list_for_each_entry(r, &mnt->mnt_mounts, mnt_child) {
1768                 struct mount *s;
1769                 if (!is_subdir(r->mnt_mountpoint, dentry))
1770                         continue;
1771 
1772                 for (s = r; s; s = next_mnt(s, r)) {
1773                         if (!(flag & CL_COPY_UNBINDABLE) &&
1774                             IS_MNT_UNBINDABLE(s)) {
1775                                 if (s->mnt.mnt_flags & MNT_LOCKED) {
1776                                         /* Both unbindable and locked. */
1777                                         q = ERR_PTR(-EPERM);
1778                                         goto out;
1779                                 } else {
1780                                         s = skip_mnt_tree(s);
1781                                         continue;
1782                                 }
1783                         }
1784                         if (!(flag & CL_COPY_MNT_NS_FILE) &&
1785                             is_mnt_ns_file(s->mnt.mnt_root)) {
1786                                 s = skip_mnt_tree(s);
1787                                 continue;
1788                         }
1789                         while (p != s->mnt_parent) {
1790                                 p = p->mnt_parent;
1791                                 q = q->mnt_parent;
1792                         }
1793                         p = s;
1794                         parent = q;
1795                         q = clone_mnt(p, p->mnt.mnt_root, flag);
1796                         if (IS_ERR(q))
1797                                 goto out;
1798                         lock_mount_hash();
1799                         list_add_tail(&q->mnt_list, &res->mnt_list);
1800                         attach_mnt(q, parent, p->mnt_mp);
1801                         unlock_mount_hash();
1802                 }
1803         }
1804         return res;
1805 out:
1806         if (res) {
1807                 lock_mount_hash();
1808                 umount_tree(res, UMOUNT_SYNC);
1809                 unlock_mount_hash();
1810         }
1811         return q;
1812 }
1813 
1814 /* Caller should check returned pointer for errors */
1815 
1816 struct vfsmount *collect_mounts(const struct path *path)
1817 {
1818         struct mount *tree;
1819         namespace_lock();
1820         if (!check_mnt(real_mount(path->mnt)))
1821                 tree = ERR_PTR(-EINVAL);
1822         else
1823                 tree = copy_tree(real_mount(path->mnt), path->dentry,
1824                                  CL_COPY_ALL | CL_PRIVATE);
1825         namespace_unlock();
1826         if (IS_ERR(tree))
1827                 return ERR_CAST(tree);
1828         return &tree->mnt;
1829 }
1830 
1831 static void free_mnt_ns(struct mnt_namespace *);
1832 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *, bool);
1833 
1834 void dissolve_on_fput(struct vfsmount *mnt)
1835 {
1836         struct mnt_namespace *ns;
1837         namespace_lock();
1838         lock_mount_hash();
1839         ns = real_mount(mnt)->mnt_ns;
1840         if (ns) {
1841                 if (is_anon_ns(ns))
1842                         umount_tree(real_mount(mnt), UMOUNT_CONNECTED);
1843                 else
1844                         ns = NULL;
1845         }
1846         unlock_mount_hash();
1847         namespace_unlock();
1848         if (ns)
1849                 free_mnt_ns(ns);
1850 }
1851 
1852 void drop_collected_mounts(struct vfsmount *mnt)
1853 {
1854         namespace_lock();
1855         lock_mount_hash();
1856         umount_tree(real_mount(mnt), 0);
1857         unlock_mount_hash();
1858         namespace_unlock();
1859 }
1860 
1861 /**
1862  * clone_private_mount - create a private clone of a path
1863  *
1864  * This creates a new vfsmount, which will be the clone of @path.  The new will
1865  * not be attached anywhere in the namespace and will be private (i.e. changes
1866  * to the originating mount won't be propagated into this).
1867  *
1868  * Release with mntput().
1869  */
1870 struct vfsmount *clone_private_mount(const struct path *path)
1871 {
1872         struct mount *old_mnt = real_mount(path->mnt);
1873         struct mount *new_mnt;
1874 
1875         if (IS_MNT_UNBINDABLE(old_mnt))
1876                 return ERR_PTR(-EINVAL);
1877 
1878         new_mnt = clone_mnt(old_mnt, path->dentry, CL_PRIVATE);
1879         if (IS_ERR(new_mnt))
1880                 return ERR_CAST(new_mnt);
1881 
1882         return &new_mnt->mnt;
1883 }
1884 EXPORT_SYMBOL_GPL(clone_private_mount);
1885 
1886 int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
1887                    struct vfsmount *root)
1888 {
1889         struct mount *mnt;
1890         int res = f(root, arg);
1891         if (res)
1892                 return res;
1893         list_for_each_entry(mnt, &real_mount(root)->mnt_list, mnt_list) {
1894                 res = f(&mnt->mnt, arg);
1895                 if (res)
1896                         return res;
1897         }
1898         return 0;
1899 }
1900 
1901 static void lock_mnt_tree(struct mount *mnt)
1902 {
1903         struct mount *p;
1904 
1905         for (p = mnt; p; p = next_mnt(p, mnt)) {
1906                 int flags = p->mnt.mnt_flags;
1907                 /* Don't allow unprivileged users to change mount flags */
1908                 flags |= MNT_LOCK_ATIME;
1909 
1910                 if (flags & MNT_READONLY)
1911                         flags |= MNT_LOCK_READONLY;
1912 
1913                 if (flags & MNT_NODEV)
1914                         flags |= MNT_LOCK_NODEV;
1915 
1916                 if (flags & MNT_NOSUID)
1917                         flags |= MNT_LOCK_NOSUID;
1918 
1919                 if (flags & MNT_NOEXEC)
1920                         flags |= MNT_LOCK_NOEXEC;
1921                 /* Don't allow unprivileged users to reveal what is under a mount */
1922                 if (list_empty(&p->mnt_expire))
1923                         flags |= MNT_LOCKED;
1924                 p->mnt.mnt_flags = flags;
1925         }
1926 }
1927 
1928 static void cleanup_group_ids(struct mount *mnt, struct mount *end)
1929 {
1930         struct mount *p;
1931 
1932         for (p = mnt; p != end; p = next_mnt(p, mnt)) {
1933                 if (p->mnt_group_id && !IS_MNT_SHARED(p))
1934                         mnt_release_group_id(p);
1935         }
1936 }
1937 
1938 static int invent_group_ids(struct mount *mnt, bool recurse)
1939 {
1940         struct mount *p;
1941 
1942         for (p = mnt; p; p = recurse ? next_mnt(p, mnt) : NULL) {
1943                 if (!p->mnt_group_id && !IS_MNT_SHARED(p)) {
1944                         int err = mnt_alloc_group_id(p);
1945                         if (err) {
1946                                 cleanup_group_ids(mnt, p);
1947                                 return err;
1948                         }
1949                 }
1950         }
1951 
1952         return 0;
1953 }
1954 
1955 int count_mounts(struct mnt_namespace *ns, struct mount *mnt)
1956 {
1957         unsigned int max = READ_ONCE(sysctl_mount_max);
1958         unsigned int mounts = 0, old, pending, sum;
1959         struct mount *p;
1960 
1961         for (p = mnt; p; p = next_mnt(p, mnt))
1962                 mounts++;
1963 
1964         old = ns->mounts;
1965         pending = ns->pending_mounts;
1966         sum = old + pending;
1967         if ((old > sum) ||
1968             (pending > sum) ||
1969             (max < sum) ||
1970             (mounts > (max - sum)))
1971                 return -ENOSPC;
1972 
1973         ns->pending_mounts = pending + mounts;
1974         return 0;
1975 }
1976 
1977 /*
1978  *  @source_mnt : mount tree to be attached
1979  *  @nd         : place the mount tree @source_mnt is attached
1980  *  @parent_nd  : if non-null, detach the source_mnt from its parent and
1981  *                 store the parent mount and mountpoint dentry.
1982  *                 (done when source_mnt is moved)
1983  *
1984  *  NOTE: in the table below explains the semantics when a source mount
1985  *  of a given type is attached to a destination mount of a given type.
1986  * ---------------------------------------------------------------------------
1987  * |         BIND MOUNT OPERATION                                            |
1988  * |**************************************************************************
1989  * | source-->| shared        |       private  |       slave    | unbindable |
1990  * | dest     |               |                |                |            |
1991  * |   |      |               |                |                |            |
1992  * |   v      |               |                |                |            |
1993  * |**************************************************************************
1994  * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
1995  * |          |               |                |                |            |
1996  * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
1997  * ***************************************************************************
1998  * A bind operation clones the source mount and mounts the clone on the
1999  * destination mount.
2000  *
2001  * (++)  the cloned mount is propagated to all the mounts in the propagation
2002  *       tree of the destination mount and the cloned mount is added to
2003  *       the peer group of the source mount.
2004  * (+)   the cloned mount is created under the destination mount and is marked
2005  *       as shared. The cloned mount is added to the peer group of the source
2006  *       mount.
2007  * (+++) the mount is propagated to all the mounts in the propagation tree
2008  *       of the destination mount and the cloned mount is made slave
2009  *       of the same master as that of the source mount. The cloned mount
2010  *       is marked as 'shared and slave'.
2011  * (*)   the cloned mount is made a slave of the same master as that of the
2012  *       source mount.
2013  *
2014  * ---------------------------------------------------------------------------
2015  * |                    MOVE MOUNT OPERATION                                 |
2016  * |**************************************************************************
2017  * | source-->| shared        |       private  |       slave    | unbindable |
2018  * | dest     |               |                |                |            |
2019  * |   |      |               |                |                |            |
2020  * |   v      |               |                |                |            |
2021  * |**************************************************************************
2022  * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
2023  * |          |               |                |                |            |
2024  * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
2025  * ***************************************************************************
2026  *
2027  * (+)  the mount is moved to the destination. And is then propagated to
2028  *      all the mounts in the propagation tree of the destination mount.
2029  * (+*)  the mount is moved to the destination.
2030  * (+++)  the mount is moved to the destination and is then propagated to
2031  *      all the mounts belonging to the destination mount's propagation tree.
2032  *      the mount is marked as 'shared and slave'.
2033  * (*)  the mount continues to be a slave at the new location.
2034  *
2035  * if the source mount is a tree, the operations explained above is
2036  * applied to each mount in the tree.
2037  * Must be called without spinlocks held, since this function can sleep
2038  * in allocations.
2039  */
2040 static int attach_recursive_mnt(struct mount *source_mnt,
2041                         struct mount *dest_mnt,
2042                         struct mountpoint *dest_mp,
2043                         bool moving)
2044 {
2045         struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
2046         HLIST_HEAD(tree_list);
2047         struct mnt_namespace *ns = dest_mnt->mnt_ns;
2048         struct mountpoint *smp;
2049         struct mount *child, *p;
2050         struct hlist_node *n;
2051         int err;
2052 
2053         /* Preallocate a mountpoint in case the new mounts need
2054          * to be tucked under other mounts.
2055          */
2056         smp = get_mountpoint(source_mnt->mnt.mnt_root);
2057         if (IS_ERR(smp))
2058                 return PTR_ERR(smp);
2059 
2060         /* Is there space to add these mounts to the mount namespace? */
2061         if (!moving) {
2062                 err = count_mounts(ns, source_mnt);
2063                 if (err)
2064                         goto out;
2065         }
2066 
2067         if (IS_MNT_SHARED(dest_mnt)) {
2068                 err = invent_group_ids(source_mnt, true);
2069                 if (err)
2070                         goto out;
2071                 err = propagate_mnt(dest_mnt, dest_mp, source_mnt, &tree_list);
2072                 lock_mount_hash();
2073                 if (err)
2074                         goto out_cleanup_ids;
2075                 for (p = source_mnt; p; p = next_mnt(p, source_mnt))
2076                         set_mnt_shared(p);
2077         } else {
2078                 lock_mount_hash();
2079         }
2080         if (moving) {
2081                 unhash_mnt(source_mnt);
2082                 attach_mnt(source_mnt, dest_mnt, dest_mp);
2083                 touch_mnt_namespace(source_mnt->mnt_ns);
2084         } else {
2085                 if (source_mnt->mnt_ns) {
2086                         /* move from anon - the caller will destroy */
2087                         list_del_init(&source_mnt->mnt_ns->list);
2088                 }
2089                 mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
2090                 commit_tree(source_mnt);
2091         }
2092 
2093         hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) {
2094                 struct mount *q;
2095                 hlist_del_init(&child->mnt_hash);
2096                 q = __lookup_mnt(&child->mnt_parent->mnt,
2097                                  child->mnt_mountpoint);
2098                 if (q)
2099                         mnt_change_mountpoint(child, smp, q);
2100                 /* Notice when we are propagating across user namespaces */
2101                 if (child->mnt_parent->mnt_ns->user_ns != user_ns)
2102                         lock_mnt_tree(child);
2103                 child->mnt.mnt_flags &= ~MNT_LOCKED;
2104                 commit_tree(child);
2105         }
2106         put_mountpoint(smp);
2107         unlock_mount_hash();
2108 
2109         return 0;
2110 
2111  out_cleanup_ids:
2112         while (!hlist_empty(&tree_list)) {
2113                 child = hlist_entry(tree_list.first, struct mount, mnt_hash);
2114                 child->mnt_parent->mnt_ns->pending_mounts = 0;
2115                 umount_tree(child, UMOUNT_SYNC);
2116         }
2117         unlock_mount_hash();
2118         cleanup_group_ids(source_mnt, NULL);
2119  out:
2120         ns->pending_mounts = 0;
2121 
2122         read_seqlock_excl(&mount_lock);
2123         put_mountpoint(smp);
2124         read_sequnlock_excl(&mount_lock);
2125 
2126         return err;
2127 }
2128 
2129 static struct mountpoint *lock_mount(struct path *path)
2130 {
2131         struct vfsmount *mnt;
2132         struct dentry *dentry = path->dentry;
2133 retry:
2134         inode_lock(dentry->d_inode);
2135         if (unlikely(cant_mount(dentry))) {
2136                 inode_unlock(dentry->d_inode);
2137                 return ERR_PTR(-ENOENT);
2138         }
2139         namespace_lock();
2140         mnt = lookup_mnt(path);
2141         if (likely(!mnt)) {
2142                 struct mountpoint *mp = get_mountpoint(dentry);
2143                 if (IS_ERR(mp)) {
2144                         namespace_unlock();
2145                         inode_unlock(dentry->d_inode);
2146                         return mp;
2147                 }
2148                 return mp;
2149         }
2150         namespace_unlock();
2151         inode_unlock(path->dentry->d_inode);
2152         path_put(path);
2153         path->mnt = mnt;
2154         dentry = path->dentry = dget(mnt->mnt_root);
2155         goto retry;
2156 }
2157 
2158 static void unlock_mount(struct mountpoint *where)
2159 {
2160         struct dentry *dentry = where->m_dentry;
2161 
2162         read_seqlock_excl(&mount_lock);
2163         put_mountpoint(where);
2164         read_sequnlock_excl(&mount_lock);
2165 
2166         namespace_unlock();
2167         inode_unlock(dentry->d_inode);
2168 }
2169 
2170 static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp)
2171 {
2172         if (mnt->mnt.mnt_sb->s_flags & SB_NOUSER)
2173                 return -EINVAL;
2174 
2175         if (d_is_dir(mp->m_dentry) !=
2176               d_is_dir(mnt->mnt.mnt_root))
2177                 return -ENOTDIR;
2178 
2179         return attach_recursive_mnt(mnt, p, mp, false);
2180 }
2181 
2182 /*
2183  * Sanity check the flags to change_mnt_propagation.
2184  */
2185 
2186 static int flags_to_propagation_type(int ms_flags)
2187 {
2188         int type = ms_flags & ~(MS_REC | MS_SILENT);
2189 
2190         /* Fail if any non-propagation flags are set */
2191         if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
2192                 return 0;
2193         /* Only one propagation flag should be set */
2194         if (!is_power_of_2(type))
2195                 return 0;
2196         return type;
2197 }
2198 
2199 /*
2200  * recursively change the type of the mountpoint.
2201  */
2202 static int do_change_type(struct path *path, int ms_flags)
2203 {
2204         struct mount *m;
2205         struct mount *mnt = real_mount(path->mnt);
2206         int recurse = ms_flags & MS_REC;
2207         int type;
2208         int err = 0;
2209 
2210         if (path->dentry != path->mnt->mnt_root)
2211                 return -EINVAL;
2212 
2213         type = flags_to_propagation_type(ms_flags);
2214         if (!type)
2215                 return -EINVAL;
2216 
2217         namespace_lock();
2218         if (type == MS_SHARED) {
2219                 err = invent_group_ids(mnt, recurse);
2220                 if (err)
2221                         goto out_unlock;
2222         }
2223 
2224         lock_mount_hash();
2225         for (m = mnt; m; m = (recurse ? next_mnt(m, mnt) : NULL))
2226                 change_mnt_propagation(m, type);
2227         unlock_mount_hash();
2228 
2229  out_unlock:
2230         namespace_unlock();
2231         return err;
2232 }
2233 
2234 static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
2235 {
2236         struct mount *child;
2237         list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
2238                 if (!is_subdir(child->mnt_mountpoint, dentry))
2239                         continue;
2240 
2241                 if (child->mnt.mnt_flags & MNT_LOCKED)
2242                         return true;
2243         }
2244         return false;
2245 }
2246 
2247 static struct mount *__do_loopback(struct path *old_path, int recurse)
2248 {
2249         struct mount *mnt = ERR_PTR(-EINVAL), *old = real_mount(old_path->mnt);
2250 
2251         if (IS_MNT_UNBINDABLE(old))
2252                 return mnt;
2253 
2254         if (!check_mnt(old) && old_path->dentry->d_op != &ns_dentry_operations)
2255                 return mnt;
2256 
2257         if (!recurse && has_locked_children(old, old_path->dentry))
2258                 return mnt;
2259 
2260         if (recurse)
2261                 mnt = copy_tree(old, old_path->dentry, CL_COPY_MNT_NS_FILE);
2262         else
2263                 mnt = clone_mnt(old, old_path->dentry, 0);
2264 
2265         if (!IS_ERR(mnt))
2266                 mnt->mnt.mnt_flags &= ~MNT_LOCKED;
2267 
2268         return mnt;
2269 }
2270 
2271 /*
2272  * do loopback mount.
2273  */
2274 static int do_loopback(struct path *path, const char *old_name,
2275                                 int recurse)
2276 {
2277         struct path old_path;
2278         struct mount *mnt = NULL, *parent;
2279         struct mountpoint *mp;
2280         int err;
2281         if (!old_name || !*old_name)
2282                 return -EINVAL;
2283         err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
2284         if (err)
2285                 return err;
2286 
2287         err = -EINVAL;
2288         if (mnt_ns_loop(old_path.dentry))
2289                 goto out;
2290 
2291         mp = lock_mount(path);
2292         if (IS_ERR(mp)) {
2293                 err = PTR_ERR(mp);
2294                 goto out;
2295         }
2296 
2297         parent = real_mount(path->mnt);
2298         if (!check_mnt(parent))
2299                 goto out2;
2300 
2301         mnt = __do_loopback(&old_path, recurse);
2302         if (IS_ERR(mnt)) {
2303                 err = PTR_ERR(mnt);
2304                 goto out2;
2305         }
2306 
2307         err = graft_tree(mnt, parent, mp);
2308         if (err) {
2309                 lock_mount_hash();
2310                 umount_tree(mnt, UMOUNT_SYNC);
2311                 unlock_mount_hash();
2312         }
2313 out2:
2314         unlock_mount(mp);
2315 out:
2316         path_put(&old_path);
2317         return err;
2318 }
2319 
2320 static struct file *open_detached_copy(struct path *path, bool recursive)
2321 {
2322         struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
2323         struct mnt_namespace *ns = alloc_mnt_ns(user_ns, true);
2324         struct mount *mnt, *p;
2325         struct file *file;
2326 
2327         if (IS_ERR(ns))
2328                 return ERR_CAST(ns);
2329 
2330         namespace_lock();
2331         mnt = __do_loopback(path, recursive);
2332         if (IS_ERR(mnt)) {
2333                 namespace_unlock();
2334                 free_mnt_ns(ns);
2335                 return ERR_CAST(mnt);
2336         }
2337 
2338         lock_mount_hash();
2339         for (p = mnt; p; p = next_mnt(p, mnt)) {
2340                 p->mnt_ns = ns;
2341                 ns->mounts++;
2342         }
2343         ns->root = mnt;
2344         list_add_tail(&ns->list, &mnt->mnt_list);
2345         mntget(&mnt->mnt);
2346         unlock_mount_hash();
2347         namespace_unlock();
2348 
2349         mntput(path->mnt);
2350         path->mnt = &mnt->mnt;
2351         file = dentry_open(path, O_PATH, current_cred());
2352         if (IS_ERR(file))
2353                 dissolve_on_fput(path->mnt);
2354         else
2355                 file->f_mode |= FMODE_NEED_UNMOUNT;
2356         return file;
2357 }
2358 
2359 SYSCALL_DEFINE3(open_tree, int, dfd, const char *, filename, unsigned, flags)
2360 {
2361         struct file *file;
2362         struct path path;
2363         int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
2364         bool detached = flags & OPEN_TREE_CLONE;
2365         int error;
2366         int fd;
2367 
2368         BUILD_BUG_ON(OPEN_TREE_CLOEXEC != O_CLOEXEC);
2369 
2370         if (flags & ~(AT_EMPTY_PATH | AT_NO_AUTOMOUNT | AT_RECURSIVE |
2371                       AT_SYMLINK_NOFOLLOW | OPEN_TREE_CLONE |
2372                       OPEN_TREE_CLOEXEC))
2373                 return -EINVAL;
2374 
2375         if ((flags & (AT_RECURSIVE | OPEN_TREE_CLONE)) == AT_RECURSIVE)
2376                 return -EINVAL;
2377 
2378         if (flags & AT_NO_AUTOMOUNT)
2379                 lookup_flags &= ~LOOKUP_AUTOMOUNT;
2380         if (flags & AT_SYMLINK_NOFOLLOW)
2381                 lookup_flags &= ~LOOKUP_FOLLOW;
2382         if (flags & AT_EMPTY_PATH)
2383                 lookup_flags |= LOOKUP_EMPTY;
2384 
2385         if (detached && !may_mount())
2386                 return -EPERM;
2387 
2388         fd = get_unused_fd_flags(flags & O_CLOEXEC);
2389         if (fd < 0)
2390                 return fd;
2391 
2392         error = user_path_at(dfd, filename, lookup_flags, &path);
2393         if (unlikely(error)) {
2394                 file = ERR_PTR(error);
2395         } else {
2396                 if (detached)
2397                         file = open_detached_copy(&path, flags & AT_RECURSIVE);
2398                 else
2399                         file = dentry_open(&path, O_PATH, current_cred());
2400                 path_put(&path);
2401         }
2402         if (IS_ERR(file)) {
2403                 put_unused_fd(fd);
2404                 return PTR_ERR(file);
2405         }
2406         fd_install(fd, file);
2407         return fd;
2408 }
2409 
2410 /*
2411  * Don't allow locked mount flags to be cleared.
2412  *
2413  * No locks need to be held here while testing the various MNT_LOCK
2414  * flags because those flags can never be cleared once they are set.
2415  */
2416 static bool can_change_locked_flags(struct mount *mnt, unsigned int mnt_flags)
2417 {
2418         unsigned int fl = mnt->mnt.mnt_flags;
2419 
2420         if ((fl & MNT_LOCK_READONLY) &&
2421             !(mnt_flags & MNT_READONLY))
2422                 return false;
2423 
2424         if ((fl & MNT_LOCK_NODEV) &&
2425             !(mnt_flags & MNT_NODEV))
2426                 return false;
2427 
2428         if ((fl & MNT_LOCK_NOSUID) &&
2429             !(mnt_flags & MNT_NOSUID))
2430                 return false;
2431 
2432         if ((fl & MNT_LOCK_NOEXEC) &&
2433             !(mnt_flags & MNT_NOEXEC))
2434                 return false;
2435 
2436         if ((fl & MNT_LOCK_ATIME) &&
2437             ((fl & MNT_ATIME_MASK) != (mnt_flags & MNT_ATIME_MASK)))
2438                 return false;
2439 
2440         return true;
2441 }
2442 
2443 static int change_mount_ro_state(struct mount *mnt, unsigned int mnt_flags)
2444 {
2445         bool readonly_request = (mnt_flags & MNT_READONLY);
2446 
2447         if (readonly_request == __mnt_is_readonly(&mnt->mnt))
2448                 return 0;
2449 
2450         if (readonly_request)
2451                 return mnt_make_readonly(mnt);
2452 
2453         return __mnt_unmake_readonly(mnt);
2454 }
2455 
2456 /*
2457  * Update the user-settable attributes on a mount.  The caller must hold
2458  * sb->s_umount for writing.
2459  */
2460 static void set_mount_attributes(struct mount *mnt, unsigned int mnt_flags)
2461 {
2462         lock_mount_hash();
2463         mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;
2464         mnt->mnt.mnt_flags = mnt_flags;
2465         touch_mnt_namespace(mnt->mnt_ns);
2466         unlock_mount_hash();
2467 }
2468 
2469 static void mnt_warn_timestamp_expiry(struct path *mountpoint, struct vfsmount *mnt)
2470 {
2471         struct super_block *sb = mnt->mnt_sb;
2472 
2473         if (!__mnt_is_readonly(mnt) &&
2474            (ktime_get_real_seconds() + TIME_UPTIME_SEC_MAX > sb->s_time_max)) {
2475                 char *buf = (char *)__get_free_page(GFP_KERNEL);
2476                 char *mntpath = buf ? d_path(mountpoint, buf, PAGE_SIZE) : ERR_PTR(-ENOMEM);
2477                 struct tm tm;
2478 
2479                 time64_to_tm(sb->s_time_max, 0, &tm);
2480 
2481                 pr_warn("%s filesystem being %s at %s supports timestamps until %04ld (0x%llx)\n",
2482                         sb->s_type->name,
2483                         is_mounted(mnt) ? "remounted" : "mounted",
2484                         mntpath,
2485                         tm.tm_year+1900, (unsigned long long)sb->s_time_max);
2486 
2487                 free_page((unsigned long)buf);
2488         }
2489 }
2490 
2491 /*
2492  * Handle reconfiguration of the mountpoint only without alteration of the
2493  * superblock it refers to.  This is triggered by specifying MS_REMOUNT|MS_BIND
2494  * to mount(2).
2495  */
2496 static int do_reconfigure_mnt(struct path *path, unsigned int mnt_flags)
2497 {
2498         struct super_block *sb = path->mnt->mnt_sb;
2499         struct mount *mnt = real_mount(path->mnt);
2500         int ret;
2501 
2502         if (!check_mnt(mnt))
2503                 return -EINVAL;
2504 
2505         if (path->dentry != mnt->mnt.mnt_root)
2506                 return -EINVAL;
2507 
2508         if (!can_change_locked_flags(mnt, mnt_flags))
2509                 return -EPERM;
2510 
2511         down_write(&sb->s_umount);
2512         ret = change_mount_ro_state(mnt, mnt_flags);
2513         if (ret == 0)
2514                 set_mount_attributes(mnt, mnt_flags);
2515         up_write(&sb->s_umount);
2516 
2517         mnt_warn_timestamp_expiry(path, &mnt->mnt);
2518 
2519         return ret;
2520 }
2521 
2522 /*
2523  * change filesystem flags. dir should be a physical root of filesystem.
2524  * If you've mounted a non-root directory somewhere and want to do remount
2525  * on it - tough luck.
2526  */
2527 static int do_remount(struct path *path, int ms_flags, int sb_flags,
2528                       int mnt_flags, void *data)
2529 {
2530         int err;
2531         struct super_block *sb = path->mnt->mnt_sb;
2532         struct mount *mnt = real_mount(path->mnt);
2533         struct fs_context *fc;
2534 
2535         if (!check_mnt(mnt))
2536                 return -EINVAL;
2537 
2538         if (path->dentry != path->mnt->mnt_root)
2539                 return -EINVAL;
2540 
2541         if (!can_change_locked_flags(mnt, mnt_flags))
2542                 return -EPERM;
2543 
2544         fc = fs_context_for_reconfigure(path->dentry, sb_flags, MS_RMT_MASK);
2545         if (IS_ERR(fc))
2546                 return PTR_ERR(fc);
2547 
2548         err = parse_monolithic_mount_data(fc, data);
2549         if (!err) {
2550                 down_write(&sb->s_umount);
2551                 err = -EPERM;
2552                 if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
2553                         err = reconfigure_super(fc);
2554                         if (!err)
2555                                 set_mount_attributes(mnt, mnt_flags);
2556                 }
2557                 up_write(&sb->s_umount);
2558         }
2559 
2560         mnt_warn_timestamp_expiry(path, &mnt->mnt);
2561 
2562         put_fs_context(fc);
2563         return err;
2564 }
2565 
2566 static inline int tree_contains_unbindable(struct mount *mnt)
2567 {
2568         struct mount *p;
2569         for (p = mnt; p; p = next_mnt(p, mnt)) {
2570                 if (IS_MNT_UNBINDABLE(p))
2571                         return 1;
2572         }
2573         return 0;
2574 }
2575 
2576 /*
2577  * Check that there aren't references to earlier/same mount namespaces in the
2578  * specified subtree.  Such references can act as pins for mount namespaces
2579  * that aren't checked by the mount-cycle checking code, thereby allowing
2580  * cycles to be made.
2581  */
2582 static bool check_for_nsfs_mounts(struct mount *subtree)
2583 {
2584         struct mount *p;
2585         bool ret = false;
2586 
2587         lock_mount_hash();
2588         for (p = subtree; p; p = next_mnt(p, subtree))
2589                 if (mnt_ns_loop(p->mnt.mnt_root))
2590                         goto out;
2591 
2592         ret = true;
2593 out:
2594         unlock_mount_hash();
2595         return ret;
2596 }
2597 
2598 static int do_move_mount(struct path *old_path, struct path *new_path)
2599 {
2600         struct mnt_namespace *ns;
2601         struct mount *p;
2602         struct mount *old;
2603         struct mount *parent;
2604         struct mountpoint *mp, *old_mp;
2605         int err;
2606         bool attached;
2607 
2608         mp = lock_mount(new_path);
2609         if (IS_ERR(mp))
2610                 return PTR_ERR(mp);
2611 
2612         old = real_mount(old_path->mnt);
2613         p = real_mount(new_path->mnt);
2614         parent = old->mnt_parent;
2615         attached = mnt_has_parent(old);
2616         old_mp = old->mnt_mp;
2617         ns = old->mnt_ns;
2618 
2619         err = -EINVAL;
2620         /* The mountpoint must be in our namespace. */
2621         if (!check_mnt(p))
2622                 goto out;
2623 
2624         /* The thing moved must be mounted... */
2625         if (!is_mounted(&old->mnt))
2626                 goto out;
2627 
2628         /* ... and either ours or the root of anon namespace */
2629         if (!(attached ? check_mnt(old) : is_anon_ns(ns)))
2630                 goto out;
2631 
2632         if (old->mnt.mnt_flags & MNT_LOCKED)
2633                 goto out;
2634 
2635         if (old_path->dentry != old_path->mnt->mnt_root)
2636                 goto out;
2637 
2638         if (d_is_dir(new_path->dentry) !=
2639             d_is_dir(old_path->dentry))
2640                 goto out;
2641         /*
2642          * Don't move a mount residing in a shared parent.
2643          */
2644         if (attached && IS_MNT_SHARED(parent))
2645                 goto out;
2646         /*
2647          * Don't move a mount tree containing unbindable mounts to a destination
2648          * mount which is shared.
2649          */
2650         if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))
2651                 goto out;
2652         err = -ELOOP;
2653         if (!check_for_nsfs_mounts(old))
2654                 goto out;
2655         for (; mnt_has_parent(p); p = p->mnt_parent)
2656                 if (p == old)
2657                         goto out;
2658 
2659         err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp,
2660                                    attached);
2661         if (err)
2662                 goto out;
2663 
2664         /* if the mount is moved, it should no longer be expire
2665          * automatically */
2666         list_del_init(&old->mnt_expire);
2667         if (attached)
2668                 put_mountpoint(old_mp);
2669 out:
2670         unlock_mount(mp);
2671         if (!err) {
2672                 if (attached)
2673                         mntput_no_expire(parent);
2674                 else
2675                         free_mnt_ns(ns);
2676         }
2677         return err;
2678 }
2679 
2680 static int do_move_mount_old(struct path *path, const char *old_name)
2681 {
2682         struct path old_path;
2683         int err;
2684 
2685         if (!old_name || !*old_name)
2686                 return -EINVAL;
2687 
2688         err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
2689         if (err)
2690                 return err;
2691 
2692         err = do_move_mount(&old_path, path);
2693         path_put(&old_path);
2694         return err;
2695 }
2696 
2697 /*
2698  * add a mount into a namespace's mount tree
2699  */
2700 static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
2701 {
2702         struct mountpoint *mp;
2703         struct mount *parent;
2704         int err;
2705 
2706         mnt_flags &= ~MNT_INTERNAL_FLAGS;
2707 
2708         mp = lock_mount(path);
2709         if (IS_ERR(mp))
2710                 return PTR_ERR(mp);
2711 
2712         parent = real_mount(path->mnt);
2713         err = -EINVAL;
2714         if (unlikely(!check_mnt(parent))) {
2715                 /* that's acceptable only for automounts done in private ns */
2716                 if (!(mnt_flags & MNT_SHRINKABLE))
2717                         goto unlock;
2718                 /* ... and for those we'd better have mountpoint still alive */
2719                 if (!parent->mnt_ns)
2720                         goto unlock;
2721         }
2722 
2723         /* Refuse the same filesystem on the same mount point */
2724         err = -EBUSY;
2725         if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb &&
2726             path->mnt->mnt_root == path->dentry)
2727                 goto unlock;
2728 
2729         err = -EINVAL;
2730         if (d_is_symlink(newmnt->mnt.mnt_root))
2731                 goto unlock;
2732 
2733         newmnt->mnt.mnt_flags = mnt_flags;
2734         err = graft_tree(newmnt, parent, mp);
2735 
2736 unlock:
2737         unlock_mount(mp);
2738         return err;
2739 }
2740 
2741 static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags);
2742 
2743 /*
2744  * Create a new mount using a superblock configuration and request it
2745  * be added to the namespace tree.
2746  */
2747 static int do_new_mount_fc(struct fs_context *fc, struct path *mountpoint,
2748                            unsigned int mnt_flags)
2749 {
2750         struct vfsmount *mnt;
2751         struct super_block *sb = fc->root->d_sb;
2752         int error;
2753 
2754         error = security_sb_kern_mount(sb);
2755         if (!error && mount_too_revealing(sb, &mnt_flags))
2756                 error = -EPERM;
2757 
2758         if (unlikely(error)) {
2759                 fc_drop_locked(fc);
2760                 return error;
2761         }
2762 
2763         up_write(&sb->s_umount);
2764 
2765         mnt = vfs_create_mount(fc);
2766         if (IS_ERR(mnt))
2767                 return PTR_ERR(mnt);
2768 
2769         mnt_warn_timestamp_expiry(mountpoint, mnt);
2770 
2771         error = do_add_mount(real_mount(mnt), mountpoint, mnt_flags);
2772         if (error < 0)
2773                 mntput(mnt);
2774         return error;
2775 }
2776 
2777 /*
2778  * create a new mount for userspace and request it to be added into the
2779  * namespace's tree
2780  */
2781 static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
2782                         int mnt_flags, const char *name, void *data)
2783 {
2784         struct file_system_type *type;
2785         struct fs_context *fc;
2786         const char *subtype = NULL;
2787         int err = 0;
2788 
2789         if (!fstype)
2790                 return -EINVAL;
2791 
2792         type = get_fs_type(fstype);
2793         if (!type)
2794                 return -ENODEV;
2795 
2796         if (type->fs_flags & FS_HAS_SUBTYPE) {
2797                 subtype = strchr(fstype, '.');
2798                 if (subtype) {
2799                         subtype++;
2800                         if (!*subtype) {
2801                                 put_filesystem(type);
2802                                 return -EINVAL;
2803                         }
2804                 }
2805         }
2806 
2807         fc = fs_context_for_mount(type, sb_flags);
2808         put_filesystem(type);
2809         if (IS_ERR(fc))
2810                 return PTR_ERR(fc);
2811 
2812         if (subtype)
2813                 err = vfs_parse_fs_string(fc, "subtype",
2814                                           subtype, strlen(subtype));
2815         if (!err && name)
2816                 err = vfs_parse_fs_string(fc, "source", name, strlen(name));
2817         if (!err)
2818                 err = parse_monolithic_mount_data(fc, data);
2819         if (!err && !mount_capable(fc))
2820                 err = -EPERM;
2821         if (!err)
2822                 err = vfs_get_tree(fc);
2823         if (!err)
2824                 err = do_new_mount_fc(fc, path, mnt_flags);
2825 
2826         put_fs_context(fc);
2827         return err;
2828 }
2829 
2830 int finish_automount(struct vfsmount *m, struct path *path)
2831 {
2832         struct mount *mnt = real_mount(m);
2833         int err;
2834         /* The new mount record should have at least 2 refs to prevent it being
2835          * expired before we get a chance to add it
2836          */
2837         BUG_ON(mnt_get_count(mnt) < 2);
2838 
2839         if (m->mnt_sb == path->mnt->mnt_sb &&
2840             m->mnt_root == path->dentry) {
2841                 err = -ELOOP;
2842                 goto fail;
2843         }
2844 
2845         err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
2846         if (!err)
2847                 return 0;
2848 fail:
2849         /* remove m from any expiration list it may be on */
2850         if (!list_empty(&mnt->mnt_expire)) {
2851                 namespace_lock();
2852                 list_del_init(&mnt->mnt_expire);
2853                 namespace_unlock();
2854         }
2855         mntput(m);
2856         mntput(m);
2857         return err;
2858 }
2859 
2860 /**
2861  * mnt_set_expiry - Put a mount on an expiration list
2862  * @mnt: The mount to list.
2863  * @expiry_list: The list to add the mount to.
2864  */
2865 void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list)
2866 {
2867         namespace_lock();
2868 
2869         list_add_tail(&real_mount(mnt)->mnt_expire, expiry_list);
2870 
2871         namespace_unlock();
2872 }
2873 EXPORT_SYMBOL(mnt_set_expiry);
2874 
2875 /*
2876  * process a list of expirable mountpoints with the intent of discarding any
2877  * mountpoints that aren't in use and haven't been touched since last we came
2878  * here
2879  */
2880 void mark_mounts_for_expiry(struct list_head *mounts)
2881 {
2882         struct mount *mnt, *next;
2883         LIST_HEAD(graveyard);
2884 
2885         if (list_empty(mounts))
2886                 return;
2887 
2888         namespace_lock();
2889         lock_mount_hash();
2890 
2891         /* extract from the expiration list every vfsmount that matches the
2892          * following criteria:
2893          * - only referenced by its parent vfsmount
2894          * - still marked for expiry (marked on the last call here; marks are
2895          *   cleared by mntput())
2896          */
2897         list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
2898                 if (!xchg(&mnt->mnt_expiry_mark, 1) ||
2899                         propagate_mount_busy(mnt, 1))
2900                         continue;
2901                 list_move(&mnt->mnt_expire, &graveyard);
2902         }
2903         while (!list_empty(&graveyard)) {
2904                 mnt = list_first_entry(&graveyard, struct mount, mnt_expire);
2905                 touch_mnt_namespace(mnt->mnt_ns);
2906                 umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
2907         }
2908         unlock_mount_hash();
2909         namespace_unlock();
2910 }
2911 
2912 EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
2913 
2914 /*
2915  * Ripoff of 'select_parent()'
2916  *
2917  * search the list of submounts for a given mountpoint, and move any
2918  * shrinkable submounts to the 'graveyard' list.
2919  */
2920 static int select_submounts(struct mount *parent, struct list_head *graveyard)
2921 {
2922         struct mount *this_parent = parent;
2923         struct list_head *next;
2924         int found = 0;
2925 
2926 repeat:
2927         next = this_parent->mnt_mounts.next;
2928 resume:
2929         while (next != &this_parent->mnt_mounts) {
2930                 struct list_head *tmp = next;
2931                 struct mount *mnt = list_entry(tmp, struct mount, mnt_child);
2932 
2933                 next = tmp->next;
2934                 if (!(mnt->mnt.mnt_flags & MNT_SHRINKABLE))
2935                         continue;
2936                 /*
2937                  * Descend a level if the d_mounts list is non-empty.
2938                  */
2939                 if (!list_empty(&mnt->mnt_mounts)) {
2940                         this_parent = mnt;
2941                         goto repeat;
2942                 }
2943 
2944                 if (!propagate_mount_busy(mnt, 1)) {
2945                         list_move_tail(&mnt->mnt_expire, graveyard);
2946                         found++;
2947                 }
2948         }
2949         /*
2950          * All done at this level ... ascend and resume the search
2951          */
2952         if (this_parent != parent) {
2953                 next = this_parent->mnt_child.next;
2954                 this_parent = this_parent->mnt_parent;
2955                 goto resume;
2956         }
2957         return found;
2958 }
2959 
2960 /*
2961  * process a list of expirable mountpoints with the intent of discarding any
2962  * submounts of a specific parent mountpoint
2963  *
2964  * mount_lock must be held for write
2965  */
2966 static void shrink_submounts(struct mount *mnt)
2967 {
2968         LIST_HEAD(graveyard);
2969         struct mount *m;
2970 
2971         /* extract submounts of 'mountpoint' from the expiration list */
2972         while (select_submounts(mnt, &graveyard)) {
2973                 while (!list_empty(&graveyard)) {
2974                         m = list_first_entry(&graveyard, struct mount,
2975                                                 mnt_expire);
2976                         touch_mnt_namespace(m->mnt_ns);
2977                         umount_tree(m, UMOUNT_PROPAGATE|UMOUNT_SYNC);
2978                 }
2979         }
2980 }
2981 
2982 /*
2983  * Some copy_from_user() implementations do not return the exact number of
2984  * bytes remaining to copy on a fault.  But copy_mount_options() requires that.
2985  * Note that this function differs from copy_from_user() in that it will oops
2986  * on bad values of `to', rather than returning a short copy.
2987  */
2988 static long exact_copy_from_user(void *to, const void __user * from,
2989                                  unsigned long n)
2990 {
2991         char *t = to;
2992         const char __user *f = from;
2993         char c;
2994 
2995         if (!access_ok(from, n))
2996                 return n;
2997 
2998         while (n) {
2999                 if (__get_user(c, f)) {
3000                         memset(t, 0, n);
3001                         break;
3002                 }
3003                 *t++ = c;
3004                 f++;
3005                 n--;
3006         }
3007         return n;
3008 }
3009 
3010 void *copy_mount_options(const void __user * data)
3011 {
3012         int i;
3013         unsigned long size;
3014         char *copy;
3015 
3016         if (!data)
3017                 return NULL;
3018 
3019         copy = kmalloc(PAGE_SIZE, GFP_KERNEL);
3020         if (!copy)
3021                 return ERR_PTR(-ENOMEM);
3022 
3023         /* We only care that *some* data at the address the user
3024          * gave us is valid.  Just in case, we'll zero
3025          * the remainder of the page.
3026          */
3027         /* copy_from_user cannot cross TASK_SIZE ! */
3028         size = TASK_SIZE - (unsigned long)untagged_addr(data);
3029         if (size > PAGE_SIZE)
3030                 size = PAGE_SIZE;
3031 
3032         i = size - exact_copy_from_user(copy, data, size);
3033         if (!i) {
3034                 kfree(copy);
3035                 return ERR_PTR(-EFAULT);
3036         }
3037         if (i != PAGE_SIZE)
3038                 memset(copy + i, 0, PAGE_SIZE - i);
3039         return copy;
3040 }
3041 
3042 char *copy_mount_string(const void __user *data)
3043 {
3044         return data ? strndup_user(data, PATH_MAX) : NULL;
3045 }
3046 
3047 /*
3048  * Flags is a 32-bit value that allows up to 31 non-fs dependent flags to
3049  * be given to the mount() call (ie: read-only, no-dev, no-suid etc).
3050  *
3051  * data is a (void *) that can point to any structure up to
3052  * PAGE_SIZE-1 bytes, which can contain arbitrary fs-dependent
3053  * information (or be NULL).
3054  *
3055  * Pre-0.97 versions of mount() didn't have a flags word.
3056  * When the flags word was introduced its top half was required
3057  * to have the magic value 0xC0ED, and this remained so until 2.4.0-test9.
3058  * Therefore, if this magic number is present, it carries no information
3059  * and must be discarded.
3060  */
3061 long do_mount(const char *dev_name, const char __user *dir_name,
3062                 const char *type_page, unsigned long flags, void *data_page)
3063 {
3064         struct path path;
3065         unsigned int mnt_flags = 0, sb_flags;
3066         int retval = 0;
3067 
3068         /* Discard magic */
3069         if ((flags & MS_MGC_MSK) == MS_MGC_VAL)
3070                 flags &= ~MS_MGC_MSK;
3071 
3072         /* Basic sanity checks */
3073         if (data_page)
3074                 ((char *)data_page)[PAGE_SIZE - 1] = 0;
3075 
3076         if (flags & MS_NOUSER)
3077                 return -EINVAL;
3078 
3079         /* ... and get the mountpoint */
3080         retval = user_path_at(AT_FDCWD, dir_name, LOOKUP_FOLLOW, &path);
3081         if (retval)
3082                 return retval;
3083 
3084         retval = security_sb_mount(dev_name, &path,
3085                                    type_page, flags, data_page);
3086         if (!retval && !may_mount())
3087                 retval = -EPERM;
3088         if (!retval && (flags & SB_MANDLOCK) && !may_mandlock())
3089                 retval = -EPERM;
3090         if (retval)
3091                 goto dput_out;
3092 
3093         /* Default to relatime unless overriden */
3094         if (!(flags & MS_NOATIME))
3095                 mnt_flags |= MNT_RELATIME;
3096 
3097         /* Separate the per-mountpoint flags */
3098         if (flags & MS_NOSUID)
3099                 mnt_flags |= MNT_NOSUID;
3100         if (flags & MS_NODEV)
3101                 mnt_flags |= MNT_NODEV;
3102         if (flags & MS_NOEXEC)
3103                 mnt_flags |= MNT_NOEXEC;
3104         if (flags & MS_NOATIME)
3105                 mnt_flags |= MNT_NOATIME;
3106         if (flags & MS_NODIRATIME)
3107                 mnt_flags |= MNT_NODIRATIME;
3108         if (flags & MS_STRICTATIME)
3109                 mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
3110         if (flags & MS_RDONLY)
3111                 mnt_flags |= MNT_READONLY;
3112 
3113         /* The default atime for remount is preservation */
3114         if ((flags & MS_REMOUNT) &&
3115             ((flags & (MS_NOATIME | MS_NODIRATIME | MS_RELATIME |
3116                        MS_STRICTATIME)) == 0)) {
3117                 mnt_flags &= ~MNT_ATIME_MASK;
3118                 mnt_flags |= path.mnt->mnt_flags & MNT_ATIME_MASK;
3119         }
3120 
3121         sb_flags = flags & (SB_RDONLY |
3122                             SB_SYNCHRONOUS |
3123                             SB_MANDLOCK |
3124                             SB_DIRSYNC |
3125                             SB_SILENT |
3126                             SB_POSIXACL |
3127                             SB_LAZYTIME |
3128                             SB_I_VERSION);
3129 
3130         if ((flags & (MS_REMOUNT | MS_BIND)) == (MS_REMOUNT | MS_BIND))
3131                 retval = do_reconfigure_mnt(&path, mnt_flags);
3132         else if (flags & MS_REMOUNT)
3133                 retval = do_remount(&path, flags, sb_flags, mnt_flags,
3134                                     data_page);
3135         else if (flags & MS_BIND)
3136                 retval = do_loopback(&path, dev_name, flags & MS_REC);
3137         else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
3138                 retval = do_change_type(&path, flags);
3139         else if (flags & MS_MOVE)
3140                 retval = do_move_mount_old(&path, dev_name);
3141         else
3142                 retval = do_new_mount(&path, type_page, sb_flags, mnt_flags,
3143                                       dev_name, data_page);
3144 dput_out:
3145         path_put(&path);
3146         return retval;
3147 }
3148 
3149 static struct ucounts *inc_mnt_namespaces(struct user_namespace *ns)
3150 {
3151         return inc_ucount(ns, current_euid(), UCOUNT_MNT_NAMESPACES);
3152 }
3153 
3154 static void dec_mnt_namespaces(struct ucounts *ucounts)
3155 {
3156         dec_ucount(ucounts, UCOUNT_MNT_NAMESPACES);
3157 }
3158 
3159 static void free_mnt_ns(struct mnt_namespace *ns)
3160 {
3161         if (!is_anon_ns(ns))
3162                 ns_free_inum(&ns->ns);
3163         dec_mnt_namespaces(ns->ucounts);
3164         put_user_ns(ns->user_ns);
3165         kfree(ns);
3166 }
3167 
3168 /*
3169  * Assign a sequence number so we can detect when we attempt to bind
3170  * mount a reference to an older mount namespace into the current
3171  * mount namespace, preventing reference counting loops.  A 64bit
3172  * number incrementing at 10Ghz will take 12,427 years to wrap which
3173  * is effectively never, so we can ignore the possibility.
3174  */
3175 static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
3176 
3177 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns, bool anon)
3178 {
3179         struct mnt_namespace *new_ns;
3180         struct ucounts *ucounts;
3181         int ret;
3182 
3183         ucounts = inc_mnt_namespaces(user_ns);
3184         if (!ucounts)
3185                 return ERR_PTR(-ENOSPC);
3186 
3187         new_ns = kzalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
3188         if (!new_ns) {
3189                 dec_mnt_namespaces(ucounts);
3190                 return ERR_PTR(-ENOMEM);
3191         }
3192         if (!anon) {
3193                 ret = ns_alloc_inum(&new_ns->ns);
3194                 if (ret) {
3195                         kfree(new_ns);
3196                         dec_mnt_namespaces(ucounts);
3197                         return ERR_PTR(ret);
3198                 }
3199         }
3200         new_ns->ns.ops = &mntns_operations;
3201         if (!anon)
3202                 new_ns->seq = atomic64_add_return(1, &mnt_ns_seq);
3203         atomic_set(&new_ns->count, 1);
3204         INIT_LIST_HEAD(&new_ns->list);
3205         init_waitqueue_head(&new_ns->poll);
3206         new_ns->user_ns = get_user_ns(user_ns);
3207         new_ns->ucounts = ucounts;
3208         return new_ns;
3209 }
3210 
3211 __latent_entropy
3212 struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
3213                 struct user_namespace *user_ns, struct fs_struct *new_fs)
3214 {
3215         struct mnt_namespace *new_ns;
3216         struct vfsmount *rootmnt = NULL, *pwdmnt = NULL;
3217         struct mount *p, *q;
3218         struct mount *old;
3219         struct mount *new;
3220         int copy_flags;
3221 
3222         BUG_ON(!ns);
3223 
3224         if (likely(!(flags & CLONE_NEWNS))) {
3225                 get_mnt_ns(ns);
3226                 return ns;
3227         }
3228 
3229         old = ns->root;
3230 
3231         new_ns = alloc_mnt_ns(user_ns, false);
3232         if (IS_ERR(new_ns))
3233                 return new_ns;
3234 
3235         namespace_lock();
3236         /* First pass: copy the tree topology */
3237         copy_flags = CL_COPY_UNBINDABLE | CL_EXPIRE;
3238         if (user_ns != ns->user_ns)
3239                 copy_flags |= CL_SHARED_TO_SLAVE;
3240         new = copy_tree(old, old->mnt.mnt_root, copy_flags);
3241         if (IS_ERR(new)) {
3242                 namespace_unlock();
3243                 free_mnt_ns(new_ns);
3244                 return ERR_CAST(new);
3245         }
3246         if (user_ns != ns->user_ns) {
3247                 lock_mount_hash();
3248                 lock_mnt_tree(new);
3249                 unlock_mount_hash();
3250         }
3251         new_ns->root = new;
3252         list_add_tail(&new_ns->list, &new->mnt_list);
3253 
3254         /*
3255          * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
3256          * as belonging to new namespace.  We have already acquired a private
3257          * fs_struct, so tsk->fs->lock is not needed.
3258          */
3259         p = old;
3260         q = new;
3261         while (p) {
3262                 q->mnt_ns = new_ns;
3263                 new_ns->mounts++;
3264                 if (new_fs) {
3265                         if (&p->mnt == new_fs->root.mnt) {
3266                                 new_fs->root.mnt = mntget(&q->mnt);
3267                                 rootmnt = &p->mnt;
3268                         }
3269                         if (&p->mnt == new_fs->pwd.mnt) {
3270                                 new_fs->pwd.mnt = mntget(&q->mnt);
3271                                 pwdmnt = &p->mnt;
3272                         }
3273                 }
3274                 p = next_mnt(p, old);
3275                 q = next_mnt(q, new);
3276                 if (!q)
3277                         break;
3278                 while (p->mnt.mnt_root != q->mnt.mnt_root)
3279                         p = next_mnt(p, old);
3280         }
3281         namespace_unlock();
3282 
3283         if (rootmnt)
3284                 mntput(rootmnt);
3285         if (pwdmnt)
3286                 mntput(pwdmnt);
3287 
3288         return new_ns;
3289 }
3290 
3291 struct dentry *mount_subtree(struct vfsmount *m, const char *name)
3292 {
3293         struct mount *mnt = real_mount(m);
3294         struct mnt_namespace *ns;
3295         struct super_block *s;
3296         struct path path;
3297         int err;
3298 
3299         ns = alloc_mnt_ns(&init_user_ns, true);
3300         if (IS_ERR(ns)) {
3301                 mntput(m);
3302                 return ERR_CAST(ns);
3303         }
3304         mnt->mnt_ns = ns;
3305         ns->root = mnt;
3306         ns->mounts++;
3307         list_add(&mnt->mnt_list, &ns->list);
3308 
3309         err = vfs_path_lookup(m->mnt_root, m,
3310                         name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
3311 
3312         put_mnt_ns(ns);
3313 
3314         if (err)
3315                 return ERR_PTR(err);
3316 
3317         /* trade a vfsmount reference for active sb one */
3318         s = path.mnt->mnt_sb;
3319         atomic_inc(&s->s_active);
3320         mntput(path.mnt);
3321         /* lock the sucker */
3322         down_write(&s->s_umount);
3323         /* ... and return the root of (sub)tree on it */
3324         return path.dentry;
3325 }
3326 EXPORT_SYMBOL(mount_subtree);
3327 
3328 int ksys_mount(const char __user *dev_name, const char __user *dir_name,
3329                const char __user *type, unsigned long flags, void __user *data)
3330 {
3331         int ret;
3332         char *kernel_type;
3333         char *kernel_dev;
3334         void *options;
3335 
3336         kernel_type = copy_mount_string(type);
3337         ret = PTR_ERR(kernel_type);
3338         if (IS_ERR(kernel_type))
3339                 goto out_type;
3340 
3341         kernel_dev = copy_mount_string(dev_name);
3342         ret = PTR_ERR(kernel_dev);
3343         if (IS_ERR(kernel_dev))
3344                 goto out_dev;
3345 
3346         options = copy_mount_options(data);
3347         ret = PTR_ERR(options);
3348         if (IS_ERR(options))
3349                 goto out_data;
3350 
3351         ret = do_mount(kernel_dev, dir_name, kernel_type, flags, options);
3352 
3353         kfree(options);
3354 out_data:
3355         kfree(kernel_dev);
3356 out_dev:
3357         kfree(kernel_type);
3358 out_type:
3359         return ret;
3360 }
3361 
3362 SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
3363                 char __user *, type, unsigned long, flags, void __user *, data)
3364 {
3365         return ksys_mount(dev_name, dir_name, type, flags, data);
3366 }
3367 
3368 /*
3369  * Create a kernel mount representation for a new, prepared superblock
3370  * (specified by fs_fd) and attach to an open_tree-like file descriptor.
3371  */
3372 SYSCALL_DEFINE3(fsmount, int, fs_fd, unsigned int, flags,
3373                 unsigned int, attr_flags)
3374 {
3375         struct mnt_namespace *ns;
3376         struct fs_context *fc;
3377         struct file *file;
3378         struct path newmount;
3379         struct mount *mnt;
3380         struct fd f;
3381         unsigned int mnt_flags = 0;
3382         long ret;
3383 
3384         if (!may_mount())
3385                 return -EPERM;
3386 
3387         if ((flags & ~(FSMOUNT_CLOEXEC)) != 0)
3388                 return -EINVAL;
3389 
3390         if (attr_flags & ~(MOUNT_ATTR_RDONLY |
3391                            MOUNT_ATTR_NOSUID |
3392                            MOUNT_ATTR_NODEV |
3393                            MOUNT_ATTR_NOEXEC |
3394                            MOUNT_ATTR__ATIME |
3395                            MOUNT_ATTR_NODIRATIME))
3396                 return -EINVAL;
3397 
3398         if (attr_flags & MOUNT_ATTR_RDONLY)
3399                 mnt_flags |= MNT_READONLY;
3400         if (attr_flags & MOUNT_ATTR_NOSUID)
3401                 mnt_flags |= MNT_NOSUID;
3402         if (attr_flags & MOUNT_ATTR_NODEV)
3403                 mnt_flags |= MNT_NODEV;
3404         if (attr_flags & MOUNT_ATTR_NOEXEC)
3405                 mnt_flags |= MNT_NOEXEC;
3406         if (attr_flags & MOUNT_ATTR_NODIRATIME)
3407                 mnt_flags |= MNT_NODIRATIME;
3408 
3409         switch (attr_flags & MOUNT_ATTR__ATIME) {
3410         case MOUNT_ATTR_STRICTATIME:
3411                 break;
3412         case MOUNT_ATTR_NOATIME:
3413                 mnt_flags |= MNT_NOATIME;
3414                 break;
3415         case MOUNT_ATTR_RELATIME:
3416                 mnt_flags |= MNT_RELATIME;
3417                 break;
3418         default:
3419                 return -EINVAL;
3420         }
3421 
3422         f = fdget(fs_fd);
3423         if (!f.file)
3424                 return -EBADF;
3425 
3426         ret = -EINVAL;
3427         if (f.file->f_op != &fscontext_fops)
3428                 goto err_fsfd;
3429 
3430         fc = f.file->private_data;
3431 
3432         ret = mutex_lock_interruptible(&fc->uapi_mutex);
3433         if (ret < 0)
3434                 goto err_fsfd;
3435 
3436         /* There must be a valid superblock or we can't mount it */
3437         ret = -EINVAL;
3438         if (!fc->root)
3439                 goto err_unlock;
3440 
3441         ret = -EPERM;
3442         if (mount_too_revealing(fc->root->d_sb, &mnt_flags)) {
3443                 pr_warn("VFS: Mount too revealing\n");
3444                 goto err_unlock;
3445         }
3446 
3447         ret = -EBUSY;
3448         if (fc->phase != FS_CONTEXT_AWAITING_MOUNT)
3449                 goto err_unlock;
3450 
3451         ret = -EPERM;
3452         if ((fc->sb_flags & SB_MANDLOCK) && !may_mandlock())
3453                 goto err_unlock;
3454 
3455         newmount.mnt = vfs_create_mount(fc);
3456         if (IS_ERR(newmount.mnt)) {
3457                 ret = PTR_ERR(newmount.mnt);
3458                 goto err_unlock;
3459         }
3460         newmount.dentry = dget(fc->root);
3461         newmount.mnt->mnt_flags = mnt_flags;
3462 
3463         /* We've done the mount bit - now move the file context into more or
3464          * less the same state as if we'd done an fspick().  We don't want to
3465          * do any memory allocation or anything like that at this point as we
3466          * don't want to have to handle any errors incurred.
3467          */
3468         vfs_clean_context(fc);
3469 
3470         ns = alloc_mnt_ns(current->nsproxy->mnt_ns->user_ns, true);
3471         if (IS_ERR(ns)) {
3472                 ret = PTR_ERR(ns);
3473                 goto err_path;
3474         }
3475         mnt = real_mount(newmount.mnt);
3476         mnt->mnt_ns = ns;
3477         ns->root = mnt;
3478         ns->mounts = 1;
3479         list_add(&mnt->mnt_list, &ns->list);
3480         mntget(newmount.mnt);
3481 
3482         /* Attach to an apparent O_PATH fd with a note that we need to unmount
3483          * it, not just simply put it.
3484          */
3485         file = dentry_open(&newmount, O_PATH, fc->cred);
3486         if (IS_ERR(file)) {
3487                 dissolve_on_fput(newmount.mnt);
3488                 ret = PTR_ERR(file);
3489                 goto err_path;
3490         }
3491         file->f_mode |= FMODE_NEED_UNMOUNT;
3492 
3493         ret = get_unused_fd_flags((flags & FSMOUNT_CLOEXEC) ? O_CLOEXEC : 0);
3494         if (ret >= 0)
3495                 fd_install(ret, file);
3496         else
3497                 fput(file);
3498 
3499 err_path:
3500         path_put(&newmount);
3501 err_unlock:
3502         mutex_unlock(&fc->uapi_mutex);
3503 err_fsfd:
3504         fdput(f);
3505         return ret;
3506 }
3507 
3508 /*
3509  * Move a mount from one place to another.  In combination with
3510  * fsopen()/fsmount() this is used to install a new mount and in combination
3511  * with open_tree(OPEN_TREE_CLONE [| AT_RECURSIVE]) it can be used to copy
3512  * a mount subtree.
3513  *
3514  * Note the flags value is a combination of MOVE_MOUNT_* flags.
3515  */
3516 SYSCALL_DEFINE5(move_mount,
3517                 int, from_dfd, const char *, from_pathname,
3518                 int, to_dfd, const char *, to_pathname,
3519                 unsigned int, flags)
3520 {
3521         struct path from_path, to_path;
3522         unsigned int lflags;
3523         int ret = 0;
3524 
3525         if (!may_mount())
3526                 return -EPERM;
3527 
3528         if (flags & ~MOVE_MOUNT__MASK)
3529                 return -EINVAL;
3530 
3531         /* If someone gives a pathname, they aren't permitted to move
3532          * from an fd that requires unmount as we can't get at the flag
3533          * to clear it afterwards.
3534          */
3535         lflags = 0;
3536         if (flags & MOVE_MOUNT_F_SYMLINKS)      lflags |= LOOKUP_FOLLOW;
3537         if (flags & MOVE_MOUNT_F_AUTOMOUNTS)    lflags |= LOOKUP_AUTOMOUNT;
3538         if (flags & MOVE_MOUNT_F_EMPTY_PATH)    lflags |= LOOKUP_EMPTY;
3539 
3540         ret = user_path_at(from_dfd, from_pathname, lflags, &from_path);
3541         if (ret < 0)
3542                 return ret;
3543 
3544         lflags = 0;
3545         if (flags & MOVE_MOUNT_T_SYMLINKS)      lflags |= LOOKUP_FOLLOW;
3546         if (flags & MOVE_MOUNT_T_AUTOMOUNTS)    lflags |= LOOKUP_AUTOMOUNT;
3547         if (flags & MOVE_MOUNT_T_EMPTY_PATH)    lflags |= LOOKUP_EMPTY;
3548 
3549         ret = user_path_at(to_dfd, to_pathname, lflags, &to_path);
3550         if (ret < 0)
3551                 goto out_from;
3552 
3553         ret = security_move_mount(&from_path, &to_path);
3554         if (ret < 0)
3555                 goto out_to;
3556 
3557         ret = do_move_mount(&from_path, &to_path);
3558 
3559 out_to:
3560         path_put(&to_path);
3561 out_from:
3562         path_put(&from_path);
3563         return ret;
3564 }
3565 
3566 /*
3567  * Return true if path is reachable from root
3568  *
3569  * namespace_sem or mount_lock is held
3570  */
3571 bool is_path_reachable(struct mount *mnt, struct dentry *dentry,
3572                          const struct path *root)
3573 {
3574         while (&mnt->mnt != root->mnt && mnt_has_parent(mnt)) {
3575                 dentry = mnt->mnt_mountpoint;
3576                 mnt = mnt->mnt_parent;
3577         }
3578         return &mnt->mnt == root->mnt && is_subdir(dentry, root->dentry);
3579 }
3580 
3581 bool path_is_under(const struct path *path1, const struct path *path2)
3582 {
3583         bool res;
3584         read_seqlock_excl(&mount_lock);
3585         res = is_path_reachable(real_mount(path1->mnt), path1->dentry, path2);
3586         read_sequnlock_excl(&mount_lock);
3587         return res;
3588 }
3589 EXPORT_SYMBOL(path_is_under);
3590 
3591 /*
3592  * pivot_root Semantics:
3593  * Moves the root file system of the current process to the directory put_old,
3594  * makes new_root as the new root file system of the current process, and sets
3595  * root/cwd of all processes which had them on the current root to new_root.
3596  *
3597  * Restrictions:
3598  * The new_root and put_old must be directories, and  must not be on the
3599  * same file  system as the current process root. The put_old  must  be
3600  * underneath new_root,  i.e. adding a non-zero number of /.. to the string
3601  * pointed to by put_old must yield the same directory as new_root. No other
3602  * file system may be mounted on put_old. After all, new_root is a mountpoint.
3603  *
3604  * Also, the current root cannot be on the 'rootfs' (initial ramfs) filesystem.
3605  * See Documentation/filesystems/ramfs-rootfs-initramfs.txt for alternatives
3606  * in this situation.
3607  *
3608  * Notes:
3609  *  - we don't move root/cwd if they are not at the root (reason: if something
3610  *    cared enough to change them, it's probably wrong to force them elsewhere)
3611  *  - it's okay to pick a root that isn't the root of a file system, e.g.
3612  *    /nfs/my_root where /nfs is the mount point. It must be a mountpoint,
3613  *    though, so you may need to say mount --bind /nfs/my_root /nfs/my_root
3614  *    first.
3615  */
3616 SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
3617                 const char __user *, put_old)
3618 {
3619         struct path new, old, root;
3620         struct mount *new_mnt, *root_mnt, *old_mnt, *root_parent, *ex_parent;
3621         struct mountpoint *old_mp, *root_mp;
3622         int error;
3623 
3624         if (!may_mount())
3625                 return -EPERM;
3626 
3627         error = user_path_at(AT_FDCWD, new_root,
3628                              LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &new);
3629         if (error)
3630                 goto out0;
3631 
3632         error = user_path_at(AT_FDCWD, put_old,
3633                              LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old);
3634         if (error)
3635                 goto out1;
3636 
3637         error = security_sb_pivotroot(&old, &new);
3638         if (error)
3639                 goto out2;
3640 
3641         get_fs_root(current->fs, &root);
3642         old_mp = lock_mount(&old);
3643         error = PTR_ERR(old_mp);
3644         if (IS_ERR(old_mp))
3645                 goto out3;
3646 
3647         error = -EINVAL;
3648         new_mnt = real_mount(new.mnt);
3649         root_mnt = real_mount(root.mnt);
3650         old_mnt = real_mount(old.mnt);
3651         ex_parent = new_mnt->mnt_parent;
3652         root_parent = root_mnt->mnt_parent;
3653         if (IS_MNT_SHARED(old_mnt) ||
3654                 IS_MNT_SHARED(ex_parent) ||
3655                 IS_MNT_SHARED(root_parent))
3656                 goto out4;
3657         if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
3658                 goto out4;
3659         if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
3660                 goto out4;
3661         error = -ENOENT;
3662         if (d_unlinked(new.dentry))
3663                 goto out4;
3664         error = -EBUSY;
3665         if (new_mnt == root_mnt || old_mnt == root_mnt)
3666                 goto out4; /* loop, on the same file system  */
3667         error = -EINVAL;
3668         if (root.mnt->mnt_root != root.dentry)
3669                 goto out4; /* not a mountpoint */
3670         if (!mnt_has_parent(root_mnt))
3671                 goto out4; /* not attached */
3672         if (new.mnt->mnt_root != new.dentry)
3673                 goto out4; /* not a mountpoint */
3674         if (!mnt_has_parent(new_mnt))
3675                 goto out4; /* not attached */
3676         /* make sure we can reach put_old from new_root */
3677         if (!is_path_reachable(old_mnt, old.dentry, &new))
3678                 goto out4;
3679         /* make certain new is below the root */
3680         if (!is_path_reachable(new_mnt, new.dentry, &root))
3681                 goto out4;
3682         lock_mount_hash();
3683         umount_mnt(new_mnt);
3684         root_mp = unhash_mnt(root_mnt);  /* we'll need its mountpoint */
3685         if (root_mnt->mnt.mnt_flags & MNT_LOCKED) {
3686                 new_mnt->mnt.mnt_flags |= MNT_LOCKED;
3687                 root_mnt->mnt.mnt_flags &= ~MNT_LOCKED;
3688         }
3689         /* mount old root on put_old */
3690         attach_mnt(root_mnt, old_mnt, old_mp);
3691         /* mount new_root on / */
3692         attach_mnt(new_mnt, root_parent, root_mp);
3693         mnt_add_count(root_parent, -1);
3694         touch_mnt_namespace(current->nsproxy->mnt_ns);
3695         /* A moved mount should not expire automatically */
3696         list_del_init(&new_mnt->mnt_expire);
3697         put_mountpoint(root_mp);
3698         unlock_mount_hash();
3699         chroot_fs_refs(&root, &new);
3700         error = 0;
3701 out4:
3702         unlock_mount(old_mp);
3703         if (!error)
3704                 mntput_no_expire(ex_parent);
3705 out3:
3706         path_put(&root);
3707 out2:
3708         path_put(&old);
3709 out1:
3710         path_put(&new);
3711 out0:
3712         return error;
3713 }
3714 
3715 static void __init init_mount_tree(void)
3716 {
3717         struct vfsmount *mnt;
3718         struct mount *m;
3719         struct mnt_namespace *ns;
3720         struct path root;
3721 
3722         mnt = vfs_kern_mount(&rootfs_fs_type, 0, "rootfs", NULL);
3723         if (IS_ERR(mnt))
3724                 panic("Can't create rootfs");
3725 
3726         ns = alloc_mnt_ns(&init_user_ns, false);
3727         if (IS_ERR(ns))
3728                 panic("Can't allocate initial namespace");
3729         m = real_mount(mnt);
3730         m->mnt_ns = ns;
3731         ns->root = m;
3732         ns->mounts = 1;
3733         list_add(&m->mnt_list, &ns->list);
3734         init_task.nsproxy->mnt_ns = ns;
3735         get_mnt_ns(ns);
3736 
3737         root.mnt = mnt;
3738         root.dentry = mnt->mnt_root;
3739         mnt->mnt_flags |= MNT_LOCKED;
3740 
3741         set_fs_pwd(current->fs, &root);
3742         set_fs_root(current->fs, &root);
3743 }
3744 
3745 void __init mnt_init(void)
3746 {
3747         int err;
3748 
3749         mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
3750                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
3751 
3752         mount_hashtable = alloc_large_system_hash("Mount-cache",
3753                                 sizeof(struct hlist_head),
3754                                 mhash_entries, 19,
3755                                 HASH_ZERO,
3756                                 &m_hash_shift, &m_hash_mask, 0, 0);
3757         mountpoint_hashtable = alloc_large_system_hash("Mountpoint-cache",
3758                                 sizeof(struct hlist_head),
3759                                 mphash_entries, 19,
3760                                 HASH_ZERO,
3761                                 &mp_hash_shift, &mp_hash_mask, 0, 0);
3762 
3763         if (!mount_hashtable || !mountpoint_hashtable)
3764                 panic("Failed to allocate mount hash table\n");
3765 
3766         kernfs_init();
3767 
3768         err = sysfs_init();
3769         if (err)
3770                 printk(KERN_WARNING "%s: sysfs_init error: %d\n",
3771                         __func__, err);
3772         fs_kobj = kobject_create_and_add("fs", NULL);
3773         if (!fs_kobj)
3774                 printk(KERN_WARNING "%s: kobj create error\n", __func__);
3775         shmem_init();
3776         init_rootfs();
3777         init_mount_tree();
3778 }
3779 
3780 void put_mnt_ns(struct mnt_namespace *ns)
3781 {
3782         if (!atomic_dec_and_test(&ns->count))
3783                 return;
3784         drop_collected_mounts(&ns->root->mnt);
3785         free_mnt_ns(ns);
3786 }
3787 
3788 struct vfsmount *kern_mount(struct file_system_type *type)
3789 {
3790         struct vfsmount *mnt;
3791         mnt = vfs_kern_mount(type, SB_KERNMOUNT, type->name, NULL);
3792         if (!IS_ERR(mnt)) {
3793                 /*
3794                  * it is a longterm mount, don't release mnt until
3795                  * we unmount before file sys is unregistered
3796                 */
3797                 real_mount(mnt)->mnt_ns = MNT_NS_INTERNAL;
3798         }
3799         return mnt;
3800 }
3801 EXPORT_SYMBOL_GPL(kern_mount);
3802 
3803 void kern_unmount(struct vfsmount *mnt)
3804 {
3805         /* release long term mount so mount point can be released */
3806         if (!IS_ERR_OR_NULL(mnt)) {
3807                 real_mount(mnt)->mnt_ns = NULL;
3808                 synchronize_rcu();      /* yecchhh... */
3809                 mntput(mnt);
3810         }
3811 }
3812 EXPORT_SYMBOL(kern_unmount);
3813 
3814 bool our_mnt(struct vfsmount *mnt)
3815 {
3816         return check_mnt(real_mount(mnt));
3817 }
3818 
3819 bool current_chrooted(void)
3820 {
3821         /* Does the current process have a non-standard root */
3822         struct path ns_root;
3823         struct path fs_root;
3824         bool chrooted;
3825 
3826         /* Find the namespace root */
3827         ns_root.mnt = &current->nsproxy->mnt_ns->root->mnt;
3828         ns_root.dentry = ns_root.mnt->mnt_root;
3829         path_get(&ns_root);
3830         while (d_mountpoint(ns_root.dentry) && follow_down_one(&ns_root))
3831                 ;
3832 
3833         get_fs_root(current->fs, &fs_root);
3834 
3835         chrooted = !path_equal(&fs_root, &ns_root);
3836 
3837         path_put(&fs_root);
3838         path_put(&ns_root);
3839 
3840         return chrooted;
3841 }
3842 
3843 static bool mnt_already_visible(struct mnt_namespace *ns,
3844                                 const struct super_block *sb,
3845                                 int *new_mnt_flags)
3846 {
3847         int new_flags = *new_mnt_flags;
3848         struct mount *mnt;
3849         bool visible = false;
3850 
3851         down_read(&namespace_sem);
3852         list_for_each_entry(mnt, &ns->list, mnt_list) {
3853                 struct mount *child;
3854                 int mnt_flags;
3855 
3856                 if (mnt->mnt.mnt_sb->s_type != sb->s_type)
3857                         continue;
3858 
3859                 /* This mount is not fully visible if it's root directory
3860                  * is not the root directory of the filesystem.
3861                  */
3862                 if (mnt->mnt.mnt_root != mnt->mnt.mnt_sb->s_root)
3863                         continue;
3864 
3865                 /* A local view of the mount flags */
3866                 mnt_flags = mnt->mnt.mnt_flags;
3867 
3868                 /* Don't miss readonly hidden in the superblock flags */
3869                 if (sb_rdonly(mnt->mnt.mnt_sb))
3870                         mnt_flags |= MNT_LOCK_READONLY;
3871 
3872                 /* Verify the mount flags are equal to or more permissive
3873                  * than the proposed new mount.
3874                  */
3875                 if ((mnt_flags & MNT_LOCK_READONLY) &&
3876                     !(new_flags & MNT_READONLY))
3877                         continue;
3878                 if ((mnt_flags & MNT_LOCK_ATIME) &&
3879                     ((mnt_flags & MNT_ATIME_MASK) != (new_flags & MNT_ATIME_MASK)))
3880                         continue;
3881 
3882                 /* This mount is not fully visible if there are any
3883                  * locked child mounts that cover anything except for
3884                  * empty directories.
3885                  */
3886                 list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
3887                         struct inode *inode = child->mnt_mountpoint->d_inode;
3888                         /* Only worry about locked mounts */
3889                         if (!(child->mnt.mnt_flags & MNT_LOCKED))
3890                                 continue;
3891                         /* Is the directory permanetly empty? */
3892                         if (!is_empty_dir_inode(inode))
3893                                 goto next;
3894                 }
3895                 /* Preserve the locked attributes */
3896                 *new_mnt_flags |= mnt_flags & (MNT_LOCK_READONLY | \
3897                                                MNT_LOCK_ATIME);
3898                 visible = true;
3899                 goto found;
3900         next:   ;
3901         }
3902 found:
3903         up_read(&namespace_sem);
3904         return visible;
3905 }
3906 
3907 static bool mount_too_revealing(const struct super_block *sb, int *new_mnt_flags)
3908 {
3909         const unsigned long required_iflags = SB_I_NOEXEC | SB_I_NODEV;
3910         struct mnt_namespace *ns = current->nsproxy->mnt_ns;
3911         unsigned long s_iflags;
3912 
3913         if (ns->user_ns == &init_user_ns)
3914                 return false;
3915 
3916         /* Can this filesystem be too revealing? */
3917         s_iflags = sb->s_iflags;
3918         if (!(s_iflags & SB_I_USERNS_VISIBLE))
3919                 return false;
3920 
3921         if ((s_iflags & required_iflags) != required_iflags) {
3922                 WARN_ONCE(1, "Expected s_iflags to contain 0x%lx\n",
3923                           required_iflags);
3924                 return true;
3925         }
3926 
3927         return !mnt_already_visible(ns, sb, new_mnt_flags);
3928 }
3929 
3930 bool mnt_may_suid(struct vfsmount *mnt)
3931 {
3932         /*
3933          * Foreign mounts (accessed via fchdir or through /proc
3934          * symlinks) are always treated as if they are nosuid.  This
3935          * prevents namespaces from trusting potentially unsafe
3936          * suid/sgid bits, file caps, or security labels that originate
3937          * in other namespaces.
3938          */
3939         return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) &&
3940                current_in_userns(mnt->mnt_sb->s_user_ns);
3941 }
3942 
3943 static struct ns_common *mntns_get(struct task_struct *task)
3944 {
3945         struct ns_common *ns = NULL;
3946         struct nsproxy *nsproxy;
3947 
3948         task_lock(task);
3949         nsproxy = task->nsproxy;
3950         if (nsproxy) {
3951                 ns = &nsproxy->mnt_ns->ns;
3952                 get_mnt_ns(to_mnt_ns(ns));
3953         }
3954         task_unlock(task);
3955 
3956         return ns;
3957 }
3958 
3959 static void mntns_put(struct ns_common *ns)
3960 {
3961         put_mnt_ns(to_mnt_ns(ns));
3962 }
3963 
3964 static int mntns_install(struct nsproxy *nsproxy, struct ns_common *ns)
3965 {
3966         struct fs_struct *fs = current->fs;
3967         struct mnt_namespace *mnt_ns = to_mnt_ns(ns), *old_mnt_ns;
3968         struct path root;
3969         int err;
3970 
3971         if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||
3972             !ns_capable(current_user_ns(), CAP_SYS_CHROOT) ||
3973             !ns_capable(current_user_ns(), CAP_SYS_ADMIN))
3974                 return -EPERM;
3975 
3976         if (is_anon_ns(mnt_ns))
3977                 return -EINVAL;
3978 
3979         if (fs->users != 1)
3980                 return -EINVAL;
3981 
3982         get_mnt_ns(mnt_ns);
3983         old_mnt_ns = nsproxy->mnt_ns;
3984         nsproxy->mnt_ns = mnt_ns;
3985 
3986         /* Find the root */
3987         err = vfs_path_lookup(mnt_ns->root->mnt.mnt_root, &mnt_ns->root->mnt,
3988                                 "/", LOOKUP_DOWN, &root);
3989         if (err) {
3990                 /* revert to old namespace */
3991                 nsproxy->mnt_ns = old_mnt_ns;
3992                 put_mnt_ns(mnt_ns);
3993                 return err;
3994         }
3995 
3996         put_mnt_ns(old_mnt_ns);
3997 
3998         /* Update the pwd and root */
3999         set_fs_pwd(fs, &root);
4000         set_fs_root(fs, &root);
4001 
4002         path_put(&root);
4003         return 0;
4004 }
4005 
4006 static struct user_namespace *mntns_owner(struct ns_common *ns)
4007 {
4008         return to_mnt_ns(ns)->user_ns;
4009 }
4010 
4011 const struct proc_ns_operations mntns_operations = {
4012         .name           = "mnt",
4013         .type           = CLONE_NEWNS,
4014         .get            = mntns_get,
4015         .put            = mntns_put,
4016         .install        = mntns_install,
4017         .owner          = mntns_owner,
4018 };