root/fs/tracefs/inode.c

DEFINITIONS

1. default_read_file
2. default_write_file
3. get_dname
4. tracefs_syscall_mkdir
5. tracefs_syscall_rmdir
6. tracefs_get_inode
7. tracefs_parse_options
8. tracefs_apply_options
9. tracefs_remount
10. tracefs_show_options
11. trace_fill_super
12. trace_mount
13. start_creating
14. failed_creating
15. end_creating
16. tracefs_create_file
17. __create_dir
18. tracefs_create_dir
19. tracefs_create_instance_dir
20. __tracefs_remove
21. tracefs_remove
22. tracefs_remove_recursive
23. tracefs_initialized
24. tracefs_init

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  inode.c - part of tracefs, a pseudo file system for activating tracing
   4  *
   5  * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
   6  *
   7  *  Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
   8  *
   9  * tracefs is the file system that is used by the tracing infrastructure.
  10  */
  11 
  12 #include <linux/module.h>
  13 #include <linux/fs.h>
  14 #include <linux/mount.h>
  15 #include <linux/kobject.h>
  16 #include <linux/namei.h>
  17 #include <linux/tracefs.h>
  18 #include <linux/fsnotify.h>
  19 #include <linux/security.h>
  20 #include <linux/seq_file.h>
  21 #include <linux/parser.h>
  22 #include <linux/magic.h>
  23 #include <linux/slab.h>
  24 
  25 #define TRACEFS_DEFAULT_MODE    0700
  26 
  27 static struct vfsmount *tracefs_mount;
  28 static int tracefs_mount_count;
  29 static bool tracefs_registered;
  30 
  31 static ssize_t default_read_file(struct file *file, char __user *buf,
  32                                  size_t count, loff_t *ppos)
  33 {
  34         return 0;
  35 }
  36 
  37 static ssize_t default_write_file(struct file *file, const char __user *buf,
  38                                    size_t count, loff_t *ppos)
  39 {
  40         return count;
  41 }
  42 
  43 static const struct file_operations tracefs_file_operations = {
  44         .read =         default_read_file,
  45         .write =        default_write_file,
  46         .open =         simple_open,
  47         .llseek =       noop_llseek,
  48 };
  49 
  50 static struct tracefs_dir_ops {
  51         int (*mkdir)(const char *name);
  52         int (*rmdir)(const char *name);
  53 } tracefs_ops __ro_after_init;
  54 
  55 static char *get_dname(struct dentry *dentry)
  56 {
  57         const char *dname;
  58         char *name;
  59         int len = dentry->d_name.len;
  60 
  61         dname = dentry->d_name.name;
  62         name = kmalloc(len + 1, GFP_KERNEL);
  63         if (!name)
  64                 return NULL;
  65         memcpy(name, dname, len);
  66         name[len] = 0;
  67         return name;
  68 }
  69 
  70 static int tracefs_syscall_mkdir(struct inode *inode, struct dentry *dentry, umode_t mode)
  71 {
  72         char *name;
  73         int ret;
  74 
  75         name = get_dname(dentry);
  76         if (!name)
  77                 return -ENOMEM;
  78 
  79         /*
  80          * The mkdir call can call the generic functions that create
  81          * the files within the tracefs system. It is up to the individual
  82          * mkdir routine to handle races.
  83          */
  84         inode_unlock(inode);
  85         ret = tracefs_ops.mkdir(name);
  86         inode_lock(inode);
  87 
  88         kfree(name);
  89 
  90         return ret;
  91 }
  92 
  93 static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
  94 {
  95         char *name;
  96         int ret;
  97 
  98         name = get_dname(dentry);
  99         if (!name)
 100                 return -ENOMEM;
 101 
 102         /*
 103          * The rmdir call can call the generic functions that create
 104          * the files within the tracefs system. It is up to the individual
 105          * rmdir routine to handle races.
 106          * This time we need to unlock not only the parent (inode) but
 107          * also the directory that is being deleted.
 108          */
 109         inode_unlock(inode);
 110         inode_unlock(dentry->d_inode);
 111 
 112         ret = tracefs_ops.rmdir(name);
 113 
 114         inode_lock_nested(inode, I_MUTEX_PARENT);
 115         inode_lock(dentry->d_inode);
 116 
 117         kfree(name);
 118 
 119         return ret;
 120 }
 121 
 122 static const struct inode_operations tracefs_dir_inode_operations = {
 123         .lookup         = simple_lookup,
 124         .mkdir          = tracefs_syscall_mkdir,
 125         .rmdir          = tracefs_syscall_rmdir,
 126 };
 127 
 128 static struct inode *tracefs_get_inode(struct super_block *sb)
 129 {
 130         struct inode *inode = new_inode(sb);
 131         if (inode) {
 132                 inode->i_ino = get_next_ino();
 133                 inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
 134         }
 135         return inode;
 136 }
 137 
 138 struct tracefs_mount_opts {
 139         kuid_t uid;
 140         kgid_t gid;
 141         umode_t mode;
 142 };
 143 
 144 enum {
 145         Opt_uid,
 146         Opt_gid,
 147         Opt_mode,
 148         Opt_err
 149 };
 150 
 151 static const match_table_t tokens = {
 152         {Opt_uid, "uid=%u"},
 153         {Opt_gid, "gid=%u"},
 154         {Opt_mode, "mode=%o"},
 155         {Opt_err, NULL}
 156 };
 157 
 158 struct tracefs_fs_info {
 159         struct tracefs_mount_opts mount_opts;
 160 };
 161 
 162 static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
 163 {
 164         substring_t args[MAX_OPT_ARGS];
 165         int option;
 166         int token;
 167         kuid_t uid;
 168         kgid_t gid;
 169         char *p;
 170 
 171         opts->mode = TRACEFS_DEFAULT_MODE;
 172 
 173         while ((p = strsep(&data, ",")) != NULL) {
 174                 if (!*p)
 175                         continue;
 176 
 177                 token = match_token(p, tokens, args);
 178                 switch (token) {
 179                 case Opt_uid:
 180                         if (match_int(&args[0], &option))
 181                                 return -EINVAL;
 182                         uid = make_kuid(current_user_ns(), option);
 183                         if (!uid_valid(uid))
 184                                 return -EINVAL;
 185                         opts->uid = uid;
 186                         break;
 187                 case Opt_gid:
 188                         if (match_int(&args[0], &option))
 189                                 return -EINVAL;
 190                         gid = make_kgid(current_user_ns(), option);
 191                         if (!gid_valid(gid))
 192                                 return -EINVAL;
 193                         opts->gid = gid;
 194                         break;
 195                 case Opt_mode:
 196                         if (match_octal(&args[0], &option))
 197                                 return -EINVAL;
 198                         opts->mode = option & S_IALLUGO;
 199                         break;
 200                 /*
 201                  * We might like to report bad mount options here;
 202                  * but traditionally tracefs has ignored all mount options
 203                  */
 204                 }
 205         }
 206 
 207         return 0;
 208 }
 209 
 210 static int tracefs_apply_options(struct super_block *sb)
 211 {
 212         struct tracefs_fs_info *fsi = sb->s_fs_info;
 213         struct inode *inode = sb->s_root->d_inode;
 214         struct tracefs_mount_opts *opts = &fsi->mount_opts;
 215 
 216         inode->i_mode &= ~S_IALLUGO;
 217         inode->i_mode |= opts->mode;
 218 
 219         inode->i_uid = opts->uid;
 220         inode->i_gid = opts->gid;
 221 
 222         return 0;
 223 }
 224 
 225 static int tracefs_remount(struct super_block *sb, int *flags, char *data)
 226 {
 227         int err;
 228         struct tracefs_fs_info *fsi = sb->s_fs_info;
 229 
 230         sync_filesystem(sb);
 231         err = tracefs_parse_options(data, &fsi->mount_opts);
 232         if (err)
 233                 goto fail;
 234 
 235         tracefs_apply_options(sb);
 236 
 237 fail:
 238         return err;
 239 }
 240 
 241 static int tracefs_show_options(struct seq_file *m, struct dentry *root)
 242 {
 243         struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
 244         struct tracefs_mount_opts *opts = &fsi->mount_opts;
 245 
 246         if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
 247                 seq_printf(m, ",uid=%u",
 248                            from_kuid_munged(&init_user_ns, opts->uid));
 249         if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
 250                 seq_printf(m, ",gid=%u",
 251                            from_kgid_munged(&init_user_ns, opts->gid));
 252         if (opts->mode != TRACEFS_DEFAULT_MODE)
 253                 seq_printf(m, ",mode=%o", opts->mode);
 254 
 255         return 0;
 256 }
 257 
 258 static const struct super_operations tracefs_super_operations = {
 259         .statfs         = simple_statfs,
 260         .remount_fs     = tracefs_remount,
 261         .show_options   = tracefs_show_options,
 262 };
 263 
 264 static int trace_fill_super(struct super_block *sb, void *data, int silent)
 265 {
 266         static const struct tree_descr trace_files[] = {{""}};
 267         struct tracefs_fs_info *fsi;
 268         int err;
 269 
 270         fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
 271         sb->s_fs_info = fsi;
 272         if (!fsi) {
 273                 err = -ENOMEM;
 274                 goto fail;
 275         }
 276 
 277         err = tracefs_parse_options(data, &fsi->mount_opts);
 278         if (err)
 279                 goto fail;
 280 
 281         err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
 282         if (err)
 283                 goto fail;
 284 
 285         sb->s_op = &tracefs_super_operations;
 286 
 287         tracefs_apply_options(sb);
 288 
 289         return 0;
 290 
 291 fail:
 292         kfree(fsi);
 293         sb->s_fs_info = NULL;
 294         return err;
 295 }
 296 
 297 static struct dentry *trace_mount(struct file_system_type *fs_type,
 298                         int flags, const char *dev_name,
 299                         void *data)
 300 {
 301         return mount_single(fs_type, flags, data, trace_fill_super);
 302 }
 303 
 304 static struct file_system_type trace_fs_type = {
 305         .owner =        THIS_MODULE,
 306         .name =         "tracefs",
 307         .mount =        trace_mount,
 308         .kill_sb =      kill_litter_super,
 309 };
 310 MODULE_ALIAS_FS("tracefs");
 311 
 312 static struct dentry *start_creating(const char *name, struct dentry *parent)
 313 {
 314         struct dentry *dentry;
 315         int error;
 316 
 317         pr_debug("tracefs: creating file '%s'\n",name);
 318 
 319         error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
 320                               &tracefs_mount_count);
 321         if (error)
 322                 return ERR_PTR(error);
 323 
 324         /* If the parent is not specified, we create it in the root.
 325          * We need the root dentry to do this, which is in the super
 326          * block. A pointer to that is in the struct vfsmount that we
 327          * have around.
 328          */
 329         if (!parent)
 330                 parent = tracefs_mount->mnt_root;
 331 
 332         inode_lock(parent->d_inode);
 333         dentry = lookup_one_len(name, parent, strlen(name));
 334         if (!IS_ERR(dentry) && dentry->d_inode) {
 335                 dput(dentry);
 336                 dentry = ERR_PTR(-EEXIST);
 337         }
 338 
 339         if (IS_ERR(dentry)) {
 340                 inode_unlock(parent->d_inode);
 341                 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 342         }
 343 
 344         return dentry;
 345 }
 346 
 347 static struct dentry *failed_creating(struct dentry *dentry)
 348 {
 349         inode_unlock(dentry->d_parent->d_inode);
 350         dput(dentry);
 351         simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 352         return NULL;
 353 }
 354 
 355 static struct dentry *end_creating(struct dentry *dentry)
 356 {
 357         inode_unlock(dentry->d_parent->d_inode);
 358         return dentry;
 359 }
 360 
 361 /**
 362  * tracefs_create_file - create a file in the tracefs filesystem
 363  * @name: a pointer to a string containing the name of the file to create.
 364  * @mode: the permission that the file should have.
 365  * @parent: a pointer to the parent dentry for this file.  This should be a
 366  *          directory dentry if set.  If this parameter is NULL, then the
 367  *          file will be created in the root of the tracefs filesystem.
 368  * @data: a pointer to something that the caller will want to get to later
 369  *        on.  The inode.i_private pointer will point to this value on
 370  *        the open() call.
 371  * @fops: a pointer to a struct file_operations that should be used for
 372  *        this file.
 373  *
 374  * This is the basic "create a file" function for tracefs.  It allows for a
 375  * wide range of flexibility in creating a file, or a directory (if you want
 376  * to create a directory, the tracefs_create_dir() function is
 377  * recommended to be used instead.)
 378  *
 379  * This function will return a pointer to a dentry if it succeeds.  This
 380  * pointer must be passed to the tracefs_remove() function when the file is
 381  * to be removed (no automatic cleanup happens if your module is unloaded,
 382  * you are responsible here.)  If an error occurs, %NULL will be returned.
 383  *
 384  * If tracefs is not enabled in the kernel, the value -%ENODEV will be
 385  * returned.
 386  */
 387 struct dentry *tracefs_create_file(const char *name, umode_t mode,
 388                                    struct dentry *parent, void *data,
 389                                    const struct file_operations *fops)
 390 {
 391         struct dentry *dentry;
 392         struct inode *inode;
 393 
 394         if (security_locked_down(LOCKDOWN_TRACEFS))
 395                 return NULL;
 396 
 397         if (!(mode & S_IFMT))
 398                 mode |= S_IFREG;
 399         BUG_ON(!S_ISREG(mode));
 400         dentry = start_creating(name, parent);
 401 
 402         if (IS_ERR(dentry))
 403                 return NULL;
 404 
 405         inode = tracefs_get_inode(dentry->d_sb);
 406         if (unlikely(!inode))
 407                 return failed_creating(dentry);
 408 
 409         inode->i_mode = mode;
 410         inode->i_fop = fops ? fops : &tracefs_file_operations;
 411         inode->i_private = data;
 412         d_instantiate(dentry, inode);
 413         fsnotify_create(dentry->d_parent->d_inode, dentry);
 414         return end_creating(dentry);
 415 }
 416 
 417 static struct dentry *__create_dir(const char *name, struct dentry *parent,
 418                                    const struct inode_operations *ops)
 419 {
 420         struct dentry *dentry = start_creating(name, parent);
 421         struct inode *inode;
 422 
 423         if (IS_ERR(dentry))
 424                 return NULL;
 425 
 426         inode = tracefs_get_inode(dentry->d_sb);
 427         if (unlikely(!inode))
 428                 return failed_creating(dentry);
 429 
 430         inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
 431         inode->i_op = ops;
 432         inode->i_fop = &simple_dir_operations;
 433 
 434         /* directory inodes start off with i_nlink == 2 (for "." entry) */
 435         inc_nlink(inode);
 436         d_instantiate(dentry, inode);
 437         inc_nlink(dentry->d_parent->d_inode);
 438         fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
 439         return end_creating(dentry);
 440 }
 441 
 442 /**
 443  * tracefs_create_dir - create a directory in the tracefs filesystem
 444  * @name: a pointer to a string containing the name of the directory to
 445  *        create.
 446  * @parent: a pointer to the parent dentry for this file.  This should be a
 447  *          directory dentry if set.  If this parameter is NULL, then the
 448  *          directory will be created in the root of the tracefs filesystem.
 449  *
 450  * This function creates a directory in tracefs with the given name.
 451  *
 452  * This function will return a pointer to a dentry if it succeeds.  This
 453  * pointer must be passed to the tracefs_remove() function when the file is
 454  * to be removed. If an error occurs, %NULL will be returned.
 455  *
 456  * If tracing is not enabled in the kernel, the value -%ENODEV will be
 457  * returned.
 458  */
 459 struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
 460 {
 461         return __create_dir(name, parent, &simple_dir_inode_operations);
 462 }
 463 
 464 /**
 465  * tracefs_create_instance_dir - create the tracing instances directory
 466  * @name: The name of the instances directory to create
 467  * @parent: The parent directory that the instances directory will exist
 468  * @mkdir: The function to call when a mkdir is performed.
 469  * @rmdir: The function to call when a rmdir is performed.
 470  *
 471  * Only one instances directory is allowed.
 472  *
 473  * The instances directory is special as it allows for mkdir and rmdir to
 474  * to be done by userspace. When a mkdir or rmdir is performed, the inode
 475  * locks are released and the methhods passed in (@mkdir and @rmdir) are
 476  * called without locks and with the name of the directory being created
 477  * within the instances directory.
 478  *
 479  * Returns the dentry of the instances directory.
 480  */
 481 __init struct dentry *tracefs_create_instance_dir(const char *name,
 482                                           struct dentry *parent,
 483                                           int (*mkdir)(const char *name),
 484                                           int (*rmdir)(const char *name))
 485 {
 486         struct dentry *dentry;
 487 
 488         /* Only allow one instance of the instances directory. */
 489         if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
 490                 return NULL;
 491 
 492         dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
 493         if (!dentry)
 494                 return NULL;
 495 
 496         tracefs_ops.mkdir = mkdir;
 497         tracefs_ops.rmdir = rmdir;
 498 
 499         return dentry;
 500 }
 501 
 502 static int __tracefs_remove(struct dentry *dentry, struct dentry *parent)
 503 {
 504         int ret = 0;
 505 
 506         if (simple_positive(dentry)) {
 507                 if (dentry->d_inode) {
 508                         dget(dentry);
 509                         switch (dentry->d_inode->i_mode & S_IFMT) {
 510                         case S_IFDIR:
 511                                 ret = simple_rmdir(parent->d_inode, dentry);
 512                                 if (!ret)
 513                                         fsnotify_rmdir(parent->d_inode, dentry);
 514                                 break;
 515                         default:
 516                                 simple_unlink(parent->d_inode, dentry);
 517                                 fsnotify_unlink(parent->d_inode, dentry);
 518                                 break;
 519                         }
 520                         if (!ret)
 521                                 d_delete(dentry);
 522                         dput(dentry);
 523                 }
 524         }
 525         return ret;
 526 }
 527 
 528 /**
 529  * tracefs_remove - removes a file or directory from the tracefs filesystem
 530  * @dentry: a pointer to a the dentry of the file or directory to be
 531  *          removed.
 532  *
 533  * This function removes a file or directory in tracefs that was previously
 534  * created with a call to another tracefs function (like
 535  * tracefs_create_file() or variants thereof.)
 536  */
 537 void tracefs_remove(struct dentry *dentry)
 538 {
 539         struct dentry *parent;
 540         int ret;
 541 
 542         if (IS_ERR_OR_NULL(dentry))
 543                 return;
 544 
 545         parent = dentry->d_parent;
 546         inode_lock(parent->d_inode);
 547         ret = __tracefs_remove(dentry, parent);
 548         inode_unlock(parent->d_inode);
 549         if (!ret)
 550                 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 551 }
 552 
 553 /**
 554  * tracefs_remove_recursive - recursively removes a directory
 555  * @dentry: a pointer to a the dentry of the directory to be removed.
 556  *
 557  * This function recursively removes a directory tree in tracefs that
 558  * was previously created with a call to another tracefs function
 559  * (like tracefs_create_file() or variants thereof.)
 560  */
 561 void tracefs_remove_recursive(struct dentry *dentry)
 562 {
 563         struct dentry *child, *parent;
 564 
 565         if (IS_ERR_OR_NULL(dentry))
 566                 return;
 567 
 568         parent = dentry;
 569  down:
 570         inode_lock(parent->d_inode);
 571  loop:
 572         /*
 573          * The parent->d_subdirs is protected by the d_lock. Outside that
 574          * lock, the child can be unlinked and set to be freed which can
 575          * use the d_u.d_child as the rcu head and corrupt this list.
 576          */
 577         spin_lock(&parent->d_lock);
 578         list_for_each_entry(child, &parent->d_subdirs, d_child) {
 579                 if (!simple_positive(child))
 580                         continue;
 581 
 582                 /* perhaps simple_empty(child) makes more sense */
 583                 if (!list_empty(&child->d_subdirs)) {
 584                         spin_unlock(&parent->d_lock);
 585                         inode_unlock(parent->d_inode);
 586                         parent = child;
 587                         goto down;
 588                 }
 589 
 590                 spin_unlock(&parent->d_lock);
 591 
 592                 if (!__tracefs_remove(child, parent))
 593                         simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 594 
 595                 /*
 596                  * The parent->d_lock protects agaist child from unlinking
 597                  * from d_subdirs. When releasing the parent->d_lock we can
 598                  * no longer trust that the next pointer is valid.
 599                  * Restart the loop. We'll skip this one with the
 600                  * simple_positive() check.
 601                  */
 602                 goto loop;
 603         }
 604         spin_unlock(&parent->d_lock);
 605 
 606         inode_unlock(parent->d_inode);
 607         child = parent;
 608         parent = parent->d_parent;
 609         inode_lock(parent->d_inode);
 610 
 611         if (child != dentry)
 612                 /* go up */
 613                 goto loop;
 614 
 615         if (!__tracefs_remove(child, parent))
 616                 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
 617         inode_unlock(parent->d_inode);
 618 }
 619 
 620 /**
 621  * tracefs_initialized - Tells whether tracefs has been registered
 622  */
 623 bool tracefs_initialized(void)
 624 {
 625         return tracefs_registered;
 626 }
 627 
 628 static int __init tracefs_init(void)
 629 {
 630         int retval;
 631 
 632         retval = sysfs_create_mount_point(kernel_kobj, "tracing");
 633         if (retval)
 634                 return -EINVAL;
 635 
 636         retval = register_filesystem(&trace_fs_type);
 637         if (!retval)
 638                 tracefs_registered = true;
 639 
 640         return retval;
 641 }
 642 core_initcall(tracefs_init);