kernel/cred.c

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