root/kernel/cred.c

DEFINITIONS

1. set_cred_subscribers
2. read_cred_subscribers
3. alter_cred_subscribers
4. put_cred_rcu
5. __put_cred
6. exit_creds
7. get_task_cred
8. cred_alloc_blank
9. prepare_creds
10. prepare_exec_creds
11. copy_creds
12. cred_cap_issubset
13. commit_creds
14. abort_creds
15. override_creds
16. revert_creds
17. cred_fscmp
18. cred_init
19. prepare_kernel_cred
20. set_security_override
21. set_security_override_from_ctx
22. set_create_files_as
23. creds_are_invalid
24. dump_invalid_creds
25. __invalid_creds
26. __validate_process_creds
27. validate_creds_for_do_exit

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Task credentials management - see Documentation/security/credentials.rst
   3  *
   4  * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7 #include <linux/export.h>
   8 #include <linux/cred.h>
   9 #include <linux/slab.h>
  10 #include <linux/sched.h>
  11 #include <linux/sched/coredump.h>
  12 #include <linux/key.h>
  13 #include <linux/keyctl.h>
  14 #include <linux/init_task.h>
  15 #include <linux/security.h>
  16 #include <linux/binfmts.h>
  17 #include <linux/cn_proc.h>
  18 #include <linux/uidgid.h>
  19 
  20 #if 0
  21 #define kdebug(FMT, ...)                                                \
  22         printk("[%-5.5s%5u] " FMT "\n",                                 \
  23                current->comm, current->pid, ##__VA_ARGS__)
  24 #else
  25 #define kdebug(FMT, ...)                                                \
  26 do {                                                                    \
  27         if (0)                                                          \
  28                 no_printk("[%-5.5s%5u] " FMT "\n",                      \
  29                           current->comm, current->pid, ##__VA_ARGS__);  \
  30 } while (0)
  31 #endif
  32 
  33 static struct kmem_cache *cred_jar;
  34 
  35 /* init to 2 - one for init_task, one to ensure it is never freed */
  36 struct group_info init_groups = { .usage = ATOMIC_INIT(2) };
  37 
  38 /*
  39  * The initial credentials for the initial task
  40  */
  41 struct cred init_cred = {
  42         .usage                  = ATOMIC_INIT(4),
  43 #ifdef CONFIG_DEBUG_CREDENTIALS
  44         .subscribers            = ATOMIC_INIT(2),
  45         .magic                  = CRED_MAGIC,
  46 #endif
  47         .uid                    = GLOBAL_ROOT_UID,
  48         .gid                    = GLOBAL_ROOT_GID,
  49         .suid                   = GLOBAL_ROOT_UID,
  50         .sgid                   = GLOBAL_ROOT_GID,
  51         .euid                   = GLOBAL_ROOT_UID,
  52         .egid                   = GLOBAL_ROOT_GID,
  53         .fsuid                  = GLOBAL_ROOT_UID,
  54         .fsgid                  = GLOBAL_ROOT_GID,
  55         .securebits             = SECUREBITS_DEFAULT,
  56         .cap_inheritable        = CAP_EMPTY_SET,
  57         .cap_permitted          = CAP_FULL_SET,
  58         .cap_effective          = CAP_FULL_SET,
  59         .cap_bset               = CAP_FULL_SET,
  60         .user                   = INIT_USER,
  61         .user_ns                = &init_user_ns,
  62         .group_info             = &init_groups,
  63 };
  64 
  65 static inline void set_cred_subscribers(struct cred *cred, int n)
  66 {
  67 #ifdef CONFIG_DEBUG_CREDENTIALS
  68         atomic_set(&cred->subscribers, n);
  69 #endif
  70 }
  71 
  72 static inline int read_cred_subscribers(const struct cred *cred)
  73 {
  74 #ifdef CONFIG_DEBUG_CREDENTIALS
  75         return atomic_read(&cred->subscribers);
  76 #else
  77         return 0;
  78 #endif
  79 }
  80 
  81 static inline void alter_cred_subscribers(const struct cred *_cred, int n)
  82 {
  83 #ifdef CONFIG_DEBUG_CREDENTIALS
  84         struct cred *cred = (struct cred *) _cred;
  85 
  86         atomic_add(n, &cred->subscribers);
  87 #endif
  88 }
  89 
  90 /*
  91  * The RCU callback to actually dispose of a set of credentials
  92  */
  93 static void put_cred_rcu(struct rcu_head *rcu)
  94 {
  95         struct cred *cred = container_of(rcu, struct cred, rcu);
  96 
  97         kdebug("put_cred_rcu(%p)", cred);
  98 
  99 #ifdef CONFIG_DEBUG_CREDENTIALS
 100         if (cred->magic != CRED_MAGIC_DEAD ||
 101             atomic_read(&cred->usage) != 0 ||
 102             read_cred_subscribers(cred) != 0)
 103                 panic("CRED: put_cred_rcu() sees %p with"
 104                       " mag %x, put %p, usage %d, subscr %d\n",
 105                       cred, cred->magic, cred->put_addr,
 106                       atomic_read(&cred->usage),
 107                       read_cred_subscribers(cred));
 108 #else
 109         if (atomic_read(&cred->usage) != 0)
 110                 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
 111                       cred, atomic_read(&cred->usage));
 112 #endif
 113 
 114         security_cred_free(cred);
 115         key_put(cred->session_keyring);
 116         key_put(cred->process_keyring);
 117         key_put(cred->thread_keyring);
 118         key_put(cred->request_key_auth);
 119         if (cred->group_info)
 120                 put_group_info(cred->group_info);
 121         free_uid(cred->user);
 122         put_user_ns(cred->user_ns);
 123         kmem_cache_free(cred_jar, cred);
 124 }
 125 
 126 /**
 127  * __put_cred - Destroy a set of credentials
 128  * @cred: The record to release
 129  *
 130  * Destroy a set of credentials on which no references remain.
 131  */
 132 void __put_cred(struct cred *cred)
 133 {
 134         kdebug("__put_cred(%p{%d,%d})", cred,
 135                atomic_read(&cred->usage),
 136                read_cred_subscribers(cred));
 137 
 138         BUG_ON(atomic_read(&cred->usage) != 0);
 139 #ifdef CONFIG_DEBUG_CREDENTIALS
 140         BUG_ON(read_cred_subscribers(cred) != 0);
 141         cred->magic = CRED_MAGIC_DEAD;
 142         cred->put_addr = __builtin_return_address(0);
 143 #endif
 144         BUG_ON(cred == current->cred);
 145         BUG_ON(cred == current->real_cred);
 146 
 147         if (cred->non_rcu)
 148                 put_cred_rcu(&cred->rcu);
 149         else
 150                 call_rcu(&cred->rcu, put_cred_rcu);
 151 }
 152 EXPORT_SYMBOL(__put_cred);
 153 
 154 /*
 155  * Clean up a task's credentials when it exits
 156  */
 157 void exit_creds(struct task_struct *tsk)
 158 {
 159         struct cred *cred;
 160 
 161         kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
 162                atomic_read(&tsk->cred->usage),
 163                read_cred_subscribers(tsk->cred));
 164 
 165         cred = (struct cred *) tsk->real_cred;
 166         tsk->real_cred = NULL;
 167         validate_creds(cred);
 168         alter_cred_subscribers(cred, -1);
 169         put_cred(cred);
 170 
 171         cred = (struct cred *) tsk->cred;
 172         tsk->cred = NULL;
 173         validate_creds(cred);
 174         alter_cred_subscribers(cred, -1);
 175         put_cred(cred);
 176 
 177 #ifdef CONFIG_KEYS_REQUEST_CACHE
 178         key_put(tsk->cached_requested_key);
 179         tsk->cached_requested_key = NULL;
 180 #endif
 181 }
 182 
 183 /**
 184  * get_task_cred - Get another task's objective credentials
 185  * @task: The task to query
 186  *
 187  * Get the objective credentials of a task, pinning them so that they can't go
 188  * away.  Accessing a task's credentials directly is not permitted.
 189  *
 190  * The caller must also make sure task doesn't get deleted, either by holding a
 191  * ref on task or by holding tasklist_lock to prevent it from being unlinked.
 192  */
 193 const struct cred *get_task_cred(struct task_struct *task)
 194 {
 195         const struct cred *cred;
 196 
 197         rcu_read_lock();
 198 
 199         do {
 200                 cred = __task_cred((task));
 201                 BUG_ON(!cred);
 202         } while (!get_cred_rcu(cred));
 203 
 204         rcu_read_unlock();
 205         return cred;
 206 }
 207 EXPORT_SYMBOL(get_task_cred);
 208 
 209 /*
 210  * Allocate blank credentials, such that the credentials can be filled in at a
 211  * later date without risk of ENOMEM.
 212  */
 213 struct cred *cred_alloc_blank(void)
 214 {
 215         struct cred *new;
 216 
 217         new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
 218         if (!new)
 219                 return NULL;
 220 
 221         atomic_set(&new->usage, 1);
 222 #ifdef CONFIG_DEBUG_CREDENTIALS
 223         new->magic = CRED_MAGIC;
 224 #endif
 225 
 226         if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
 227                 goto error;
 228 
 229         return new;
 230 
 231 error:
 232         abort_creds(new);
 233         return NULL;
 234 }
 235 
 236 /**
 237  * prepare_creds - Prepare a new set of credentials for modification
 238  *
 239  * Prepare a new set of task credentials for modification.  A task's creds
 240  * shouldn't generally be modified directly, therefore this function is used to
 241  * prepare a new copy, which the caller then modifies and then commits by
 242  * calling commit_creds().
 243  *
 244  * Preparation involves making a copy of the objective creds for modification.
 245  *
 246  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
 247  *
 248  * Call commit_creds() or abort_creds() to clean up.
 249  */
 250 struct cred *prepare_creds(void)
 251 {
 252         struct task_struct *task = current;
 253         const struct cred *old;
 254         struct cred *new;
 255 
 256         validate_process_creds();
 257 
 258         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 259         if (!new)
 260                 return NULL;
 261 
 262         kdebug("prepare_creds() alloc %p", new);
 263 
 264         old = task->cred;
 265         memcpy(new, old, sizeof(struct cred));
 266 
 267         new->non_rcu = 0;
 268         atomic_set(&new->usage, 1);
 269         set_cred_subscribers(new, 0);
 270         get_group_info(new->group_info);
 271         get_uid(new->user);
 272         get_user_ns(new->user_ns);
 273 
 274 #ifdef CONFIG_KEYS
 275         key_get(new->session_keyring);
 276         key_get(new->process_keyring);
 277         key_get(new->thread_keyring);
 278         key_get(new->request_key_auth);
 279 #endif
 280 
 281 #ifdef CONFIG_SECURITY
 282         new->security = NULL;
 283 #endif
 284 
 285         if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
 286                 goto error;
 287         validate_creds(new);
 288         return new;
 289 
 290 error:
 291         abort_creds(new);
 292         return NULL;
 293 }
 294 EXPORT_SYMBOL(prepare_creds);
 295 
 296 /*
 297  * Prepare credentials for current to perform an execve()
 298  * - The caller must hold ->cred_guard_mutex
 299  */
 300 struct cred *prepare_exec_creds(void)
 301 {
 302         struct cred *new;
 303 
 304         new = prepare_creds();
 305         if (!new)
 306                 return new;
 307 
 308 #ifdef CONFIG_KEYS
 309         /* newly exec'd tasks don't get a thread keyring */
 310         key_put(new->thread_keyring);
 311         new->thread_keyring = NULL;
 312 
 313         /* inherit the session keyring; new process keyring */
 314         key_put(new->process_keyring);
 315         new->process_keyring = NULL;
 316 #endif
 317 
 318         return new;
 319 }
 320 
 321 /*
 322  * Copy credentials for the new process created by fork()
 323  *
 324  * We share if we can, but under some circumstances we have to generate a new
 325  * set.
 326  *
 327  * The new process gets the current process's subjective credentials as its
 328  * objective and subjective credentials
 329  */
 330 int copy_creds(struct task_struct *p, unsigned long clone_flags)
 331 {
 332         struct cred *new;
 333         int ret;
 334 
 335 #ifdef CONFIG_KEYS_REQUEST_CACHE
 336         p->cached_requested_key = NULL;
 337 #endif
 338 
 339         if (
 340 #ifdef CONFIG_KEYS
 341                 !p->cred->thread_keyring &&
 342 #endif
 343                 clone_flags & CLONE_THREAD
 344             ) {
 345                 p->real_cred = get_cred(p->cred);
 346                 get_cred(p->cred);
 347                 alter_cred_subscribers(p->cred, 2);
 348                 kdebug("share_creds(%p{%d,%d})",
 349                        p->cred, atomic_read(&p->cred->usage),
 350                        read_cred_subscribers(p->cred));
 351                 atomic_inc(&p->cred->user->processes);
 352                 return 0;
 353         }
 354 
 355         new = prepare_creds();
 356         if (!new)
 357                 return -ENOMEM;
 358 
 359         if (clone_flags & CLONE_NEWUSER) {
 360                 ret = create_user_ns(new);
 361                 if (ret < 0)
 362                         goto error_put;
 363         }
 364 
 365 #ifdef CONFIG_KEYS
 366         /* new threads get their own thread keyrings if their parent already
 367          * had one */
 368         if (new->thread_keyring) {
 369                 key_put(new->thread_keyring);
 370                 new->thread_keyring = NULL;
 371                 if (clone_flags & CLONE_THREAD)
 372                         install_thread_keyring_to_cred(new);
 373         }
 374 
 375         /* The process keyring is only shared between the threads in a process;
 376          * anything outside of those threads doesn't inherit.
 377          */
 378         if (!(clone_flags & CLONE_THREAD)) {
 379                 key_put(new->process_keyring);
 380                 new->process_keyring = NULL;
 381         }
 382 #endif
 383 
 384         atomic_inc(&new->user->processes);
 385         p->cred = p->real_cred = get_cred(new);
 386         alter_cred_subscribers(new, 2);
 387         validate_creds(new);
 388         return 0;
 389 
 390 error_put:
 391         put_cred(new);
 392         return ret;
 393 }
 394 
 395 static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
 396 {
 397         const struct user_namespace *set_ns = set->user_ns;
 398         const struct user_namespace *subset_ns = subset->user_ns;
 399 
 400         /* If the two credentials are in the same user namespace see if
 401          * the capabilities of subset are a subset of set.
 402          */
 403         if (set_ns == subset_ns)
 404                 return cap_issubset(subset->cap_permitted, set->cap_permitted);
 405 
 406         /* The credentials are in a different user namespaces
 407          * therefore one is a subset of the other only if a set is an
 408          * ancestor of subset and set->euid is owner of subset or one
 409          * of subsets ancestors.
 410          */
 411         for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
 412                 if ((set_ns == subset_ns->parent)  &&
 413                     uid_eq(subset_ns->owner, set->euid))
 414                         return true;
 415         }
 416 
 417         return false;
 418 }
 419 
 420 /**
 421  * commit_creds - Install new credentials upon the current task
 422  * @new: The credentials to be assigned
 423  *
 424  * Install a new set of credentials to the current task, using RCU to replace
 425  * the old set.  Both the objective and the subjective credentials pointers are
 426  * updated.  This function may not be called if the subjective credentials are
 427  * in an overridden state.
 428  *
 429  * This function eats the caller's reference to the new credentials.
 430  *
 431  * Always returns 0 thus allowing this function to be tail-called at the end
 432  * of, say, sys_setgid().
 433  */
 434 int commit_creds(struct cred *new)
 435 {
 436         struct task_struct *task = current;
 437         const struct cred *old = task->real_cred;
 438 
 439         kdebug("commit_creds(%p{%d,%d})", new,
 440                atomic_read(&new->usage),
 441                read_cred_subscribers(new));
 442 
 443         BUG_ON(task->cred != old);
 444 #ifdef CONFIG_DEBUG_CREDENTIALS
 445         BUG_ON(read_cred_subscribers(old) < 2);
 446         validate_creds(old);
 447         validate_creds(new);
 448 #endif
 449         BUG_ON(atomic_read(&new->usage) < 1);
 450 
 451         get_cred(new); /* we will require a ref for the subj creds too */
 452 
 453         /* dumpability changes */
 454         if (!uid_eq(old->euid, new->euid) ||
 455             !gid_eq(old->egid, new->egid) ||
 456             !uid_eq(old->fsuid, new->fsuid) ||
 457             !gid_eq(old->fsgid, new->fsgid) ||
 458             !cred_cap_issubset(old, new)) {
 459                 if (task->mm)
 460                         set_dumpable(task->mm, suid_dumpable);
 461                 task->pdeath_signal = 0;
 462                 /*
 463                  * If a task drops privileges and becomes nondumpable,
 464                  * the dumpability change must become visible before
 465                  * the credential change; otherwise, a __ptrace_may_access()
 466                  * racing with this change may be able to attach to a task it
 467                  * shouldn't be able to attach to (as if the task had dropped
 468                  * privileges without becoming nondumpable).
 469                  * Pairs with a read barrier in __ptrace_may_access().
 470                  */
 471                 smp_wmb();
 472         }
 473 
 474         /* alter the thread keyring */
 475         if (!uid_eq(new->fsuid, old->fsuid))
 476                 key_fsuid_changed(new);
 477         if (!gid_eq(new->fsgid, old->fsgid))
 478                 key_fsgid_changed(new);
 479 
 480         /* do it
 481          * RLIMIT_NPROC limits on user->processes have already been checked
 482          * in set_user().
 483          */
 484         alter_cred_subscribers(new, 2);
 485         if (new->user != old->user)
 486                 atomic_inc(&new->user->processes);
 487         rcu_assign_pointer(task->real_cred, new);
 488         rcu_assign_pointer(task->cred, new);
 489         if (new->user != old->user)
 490                 atomic_dec(&old->user->processes);
 491         alter_cred_subscribers(old, -2);
 492 
 493         /* send notifications */
 494         if (!uid_eq(new->uid,   old->uid)  ||
 495             !uid_eq(new->euid,  old->euid) ||
 496             !uid_eq(new->suid,  old->suid) ||
 497             !uid_eq(new->fsuid, old->fsuid))
 498                 proc_id_connector(task, PROC_EVENT_UID);
 499 
 500         if (!gid_eq(new->gid,   old->gid)  ||
 501             !gid_eq(new->egid,  old->egid) ||
 502             !gid_eq(new->sgid,  old->sgid) ||
 503             !gid_eq(new->fsgid, old->fsgid))
 504                 proc_id_connector(task, PROC_EVENT_GID);
 505 
 506         /* release the old obj and subj refs both */
 507         put_cred(old);
 508         put_cred(old);
 509         return 0;
 510 }
 511 EXPORT_SYMBOL(commit_creds);
 512 
 513 /**
 514  * abort_creds - Discard a set of credentials and unlock the current task
 515  * @new: The credentials that were going to be applied
 516  *
 517  * Discard a set of credentials that were under construction and unlock the
 518  * current task.
 519  */
 520 void abort_creds(struct cred *new)
 521 {
 522         kdebug("abort_creds(%p{%d,%d})", new,
 523                atomic_read(&new->usage),
 524                read_cred_subscribers(new));
 525 
 526 #ifdef CONFIG_DEBUG_CREDENTIALS
 527         BUG_ON(read_cred_subscribers(new) != 0);
 528 #endif
 529         BUG_ON(atomic_read(&new->usage) < 1);
 530         put_cred(new);
 531 }
 532 EXPORT_SYMBOL(abort_creds);
 533 
 534 /**
 535  * override_creds - Override the current process's subjective credentials
 536  * @new: The credentials to be assigned
 537  *
 538  * Install a set of temporary override subjective credentials on the current
 539  * process, returning the old set for later reversion.
 540  */
 541 const struct cred *override_creds(const struct cred *new)
 542 {
 543         const struct cred *old = current->cred;
 544 
 545         kdebug("override_creds(%p{%d,%d})", new,
 546                atomic_read(&new->usage),
 547                read_cred_subscribers(new));
 548 
 549         validate_creds(old);
 550         validate_creds(new);
 551 
 552         /*
 553          * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'.
 554          *
 555          * That means that we do not clear the 'non_rcu' flag, since
 556          * we are only installing the cred into the thread-synchronous
 557          * '->cred' pointer, not the '->real_cred' pointer that is
 558          * visible to other threads under RCU.
 559          *
 560          * Also note that we did validate_creds() manually, not depending
 561          * on the validation in 'get_cred()'.
 562          */
 563         get_new_cred((struct cred *)new);
 564         alter_cred_subscribers(new, 1);
 565         rcu_assign_pointer(current->cred, new);
 566         alter_cred_subscribers(old, -1);
 567 
 568         kdebug("override_creds() = %p{%d,%d}", old,
 569                atomic_read(&old->usage),
 570                read_cred_subscribers(old));
 571         return old;
 572 }
 573 EXPORT_SYMBOL(override_creds);
 574 
 575 /**
 576  * revert_creds - Revert a temporary subjective credentials override
 577  * @old: The credentials to be restored
 578  *
 579  * Revert a temporary set of override subjective credentials to an old set,
 580  * discarding the override set.
 581  */
 582 void revert_creds(const struct cred *old)
 583 {
 584         const struct cred *override = current->cred;
 585 
 586         kdebug("revert_creds(%p{%d,%d})", old,
 587                atomic_read(&old->usage),
 588                read_cred_subscribers(old));
 589 
 590         validate_creds(old);
 591         validate_creds(override);
 592         alter_cred_subscribers(old, 1);
 593         rcu_assign_pointer(current->cred, old);
 594         alter_cred_subscribers(override, -1);
 595         put_cred(override);
 596 }
 597 EXPORT_SYMBOL(revert_creds);
 598 
 599 /**
 600  * cred_fscmp - Compare two credentials with respect to filesystem access.
 601  * @a: The first credential
 602  * @b: The second credential
 603  *
 604  * cred_cmp() will return zero if both credentials have the same
 605  * fsuid, fsgid, and supplementary groups.  That is, if they will both
 606  * provide the same access to files based on mode/uid/gid.
 607  * If the credentials are different, then either -1 or 1 will
 608  * be returned depending on whether @a comes before or after @b
 609  * respectively in an arbitrary, but stable, ordering of credentials.
 610  *
 611  * Return: -1, 0, or 1 depending on comparison
 612  */
 613 int cred_fscmp(const struct cred *a, const struct cred *b)
 614 {
 615         struct group_info *ga, *gb;
 616         int g;
 617 
 618         if (a == b)
 619                 return 0;
 620         if (uid_lt(a->fsuid, b->fsuid))
 621                 return -1;
 622         if (uid_gt(a->fsuid, b->fsuid))
 623                 return 1;
 624 
 625         if (gid_lt(a->fsgid, b->fsgid))
 626                 return -1;
 627         if (gid_gt(a->fsgid, b->fsgid))
 628                 return 1;
 629 
 630         ga = a->group_info;
 631         gb = b->group_info;
 632         if (ga == gb)
 633                 return 0;
 634         if (ga == NULL)
 635                 return -1;
 636         if (gb == NULL)
 637                 return 1;
 638         if (ga->ngroups < gb->ngroups)
 639                 return -1;
 640         if (ga->ngroups > gb->ngroups)
 641                 return 1;
 642 
 643         for (g = 0; g < ga->ngroups; g++) {
 644                 if (gid_lt(ga->gid[g], gb->gid[g]))
 645                         return -1;
 646                 if (gid_gt(ga->gid[g], gb->gid[g]))
 647                         return 1;
 648         }
 649         return 0;
 650 }
 651 EXPORT_SYMBOL(cred_fscmp);
 652 
 653 /*
 654  * initialise the credentials stuff
 655  */
 656 void __init cred_init(void)
 657 {
 658         /* allocate a slab in which we can store credentials */
 659         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred), 0,
 660                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
 661 }
 662 
 663 /**
 664  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
 665  * @daemon: A userspace daemon to be used as a reference
 666  *
 667  * Prepare a set of credentials for a kernel service.  This can then be used to
 668  * override a task's own credentials so that work can be done on behalf of that
 669  * task that requires a different subjective context.
 670  *
 671  * @daemon is used to provide a base for the security record, but can be NULL.
 672  * If @daemon is supplied, then the security data will be derived from that;
 673  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
 674  *
 675  * The caller may change these controls afterwards if desired.
 676  *
 677  * Returns the new credentials or NULL if out of memory.
 678  *
 679  * Does not take, and does not return holding current->cred_replace_mutex.
 680  */
 681 struct cred *prepare_kernel_cred(struct task_struct *daemon)
 682 {
 683         const struct cred *old;
 684         struct cred *new;
 685 
 686         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 687         if (!new)
 688                 return NULL;
 689 
 690         kdebug("prepare_kernel_cred() alloc %p", new);
 691 
 692         if (daemon)
 693                 old = get_task_cred(daemon);
 694         else
 695                 old = get_cred(&init_cred);
 696 
 697         validate_creds(old);
 698 
 699         *new = *old;
 700         new->non_rcu = 0;
 701         atomic_set(&new->usage, 1);
 702         set_cred_subscribers(new, 0);
 703         get_uid(new->user);
 704         get_user_ns(new->user_ns);
 705         get_group_info(new->group_info);
 706 
 707 #ifdef CONFIG_KEYS
 708         new->session_keyring = NULL;
 709         new->process_keyring = NULL;
 710         new->thread_keyring = NULL;
 711         new->request_key_auth = NULL;
 712         new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 713 #endif
 714 
 715 #ifdef CONFIG_SECURITY
 716         new->security = NULL;
 717 #endif
 718         if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
 719                 goto error;
 720 
 721         put_cred(old);
 722         validate_creds(new);
 723         return new;
 724 
 725 error:
 726         put_cred(new);
 727         put_cred(old);
 728         return NULL;
 729 }
 730 EXPORT_SYMBOL(prepare_kernel_cred);
 731 
 732 /**
 733  * set_security_override - Set the security ID in a set of credentials
 734  * @new: The credentials to alter
 735  * @secid: The LSM security ID to set
 736  *
 737  * Set the LSM security ID in a set of credentials so that the subjective
 738  * security is overridden when an alternative set of credentials is used.
 739  */
 740 int set_security_override(struct cred *new, u32 secid)
 741 {
 742         return security_kernel_act_as(new, secid);
 743 }
 744 EXPORT_SYMBOL(set_security_override);
 745 
 746 /**
 747  * set_security_override_from_ctx - Set the security ID in a set of credentials
 748  * @new: The credentials to alter
 749  * @secctx: The LSM security context to generate the security ID from.
 750  *
 751  * Set the LSM security ID in a set of credentials so that the subjective
 752  * security is overridden when an alternative set of credentials is used.  The
 753  * security ID is specified in string form as a security context to be
 754  * interpreted by the LSM.
 755  */
 756 int set_security_override_from_ctx(struct cred *new, const char *secctx)
 757 {
 758         u32 secid;
 759         int ret;
 760 
 761         ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
 762         if (ret < 0)
 763                 return ret;
 764 
 765         return set_security_override(new, secid);
 766 }
 767 EXPORT_SYMBOL(set_security_override_from_ctx);
 768 
 769 /**
 770  * set_create_files_as - Set the LSM file create context in a set of credentials
 771  * @new: The credentials to alter
 772  * @inode: The inode to take the context from
 773  *
 774  * Change the LSM file creation context in a set of credentials to be the same
 775  * as the object context of the specified inode, so that the new inodes have
 776  * the same MAC context as that inode.
 777  */
 778 int set_create_files_as(struct cred *new, struct inode *inode)
 779 {
 780         if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
 781                 return -EINVAL;
 782         new->fsuid = inode->i_uid;
 783         new->fsgid = inode->i_gid;
 784         return security_kernel_create_files_as(new, inode);
 785 }
 786 EXPORT_SYMBOL(set_create_files_as);
 787 
 788 #ifdef CONFIG_DEBUG_CREDENTIALS
 789 
 790 bool creds_are_invalid(const struct cred *cred)
 791 {
 792         if (cred->magic != CRED_MAGIC)
 793                 return true;
 794         return false;
 795 }
 796 EXPORT_SYMBOL(creds_are_invalid);
 797 
 798 /*
 799  * dump invalid credentials
 800  */
 801 static void dump_invalid_creds(const struct cred *cred, const char *label,
 802                                const struct task_struct *tsk)
 803 {
 804         printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
 805                label, cred,
 806                cred == &init_cred ? "[init]" : "",
 807                cred == tsk->real_cred ? "[real]" : "",
 808                cred == tsk->cred ? "[eff]" : "");
 809         printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
 810                cred->magic, cred->put_addr);
 811         printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
 812                atomic_read(&cred->usage),
 813                read_cred_subscribers(cred));
 814         printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
 815                 from_kuid_munged(&init_user_ns, cred->uid),
 816                 from_kuid_munged(&init_user_ns, cred->euid),
 817                 from_kuid_munged(&init_user_ns, cred->suid),
 818                 from_kuid_munged(&init_user_ns, cred->fsuid));
 819         printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
 820                 from_kgid_munged(&init_user_ns, cred->gid),
 821                 from_kgid_munged(&init_user_ns, cred->egid),
 822                 from_kgid_munged(&init_user_ns, cred->sgid),
 823                 from_kgid_munged(&init_user_ns, cred->fsgid));
 824 #ifdef CONFIG_SECURITY
 825         printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
 826         if ((unsigned long) cred->security >= PAGE_SIZE &&
 827             (((unsigned long) cred->security & 0xffffff00) !=
 828              (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
 829                 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
 830                        ((u32*)cred->security)[0],
 831                        ((u32*)cred->security)[1]);
 832 #endif
 833 }
 834 
 835 /*
 836  * report use of invalid credentials
 837  */
 838 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
 839 {
 840         printk(KERN_ERR "CRED: Invalid credentials\n");
 841         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 842         dump_invalid_creds(cred, "Specified", current);
 843         BUG();
 844 }
 845 EXPORT_SYMBOL(__invalid_creds);
 846 
 847 /*
 848  * check the credentials on a process
 849  */
 850 void __validate_process_creds(struct task_struct *tsk,
 851                               const char *file, unsigned line)
 852 {
 853         if (tsk->cred == tsk->real_cred) {
 854                 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
 855                              creds_are_invalid(tsk->cred)))
 856                         goto invalid_creds;
 857         } else {
 858                 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
 859                              read_cred_subscribers(tsk->cred) < 1 ||
 860                              creds_are_invalid(tsk->real_cred) ||
 861                              creds_are_invalid(tsk->cred)))
 862                         goto invalid_creds;
 863         }
 864         return;
 865 
 866 invalid_creds:
 867         printk(KERN_ERR "CRED: Invalid process credentials\n");
 868         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 869 
 870         dump_invalid_creds(tsk->real_cred, "Real", tsk);
 871         if (tsk->cred != tsk->real_cred)
 872                 dump_invalid_creds(tsk->cred, "Effective", tsk);
 873         else
 874                 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
 875         BUG();
 876 }
 877 EXPORT_SYMBOL(__validate_process_creds);
 878 
 879 /*
 880  * check creds for do_exit()
 881  */
 882 void validate_creds_for_do_exit(struct task_struct *tsk)
 883 {
 884         kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
 885                tsk->real_cred, tsk->cred,
 886                atomic_read(&tsk->cred->usage),
 887                read_cred_subscribers(tsk->cred));
 888 
 889         __validate_process_creds(tsk, __FILE__, __LINE__);
 890 }
 891 
 892 #endif /* CONFIG_DEBUG_CREDENTIALS */