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