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 static 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         .ucounts                = &init_ucounts,
  64 };
  65
  66 static inline void set_cred_subscribers(struct cred *cred, int n)
  67 {
  68 #ifdef CONFIG_DEBUG_CREDENTIALS
  69         atomic_set(&cred->subscribers, n);
  70 #endif
  71 }
  72
  73 static inline int read_cred_subscribers(const struct cred *cred)
  74 {
  75 #ifdef CONFIG_DEBUG_CREDENTIALS
  76         return atomic_read(&cred->subscribers);
  77 #else
  78         return 0;
  79 #endif
  80 }
  81
  82 static inline void alter_cred_subscribers(const struct cred *_cred, int n)
  83 {
  84 #ifdef CONFIG_DEBUG_CREDENTIALS
  85         struct cred *cred = (struct cred *) _cred;
  86
  87         atomic_add(n, &cred->subscribers);
  88 #endif
  89 }
  90
  91 /*
  92  * The RCU callback to actually dispose of a set of credentials
  93  */
  94 static void put_cred_rcu(struct rcu_head *rcu)
  95 {
  96         struct cred *cred = container_of(rcu, struct cred, rcu);
  97
  98         kdebug("put_cred_rcu(%p)", cred);
  99
 100 #ifdef CONFIG_DEBUG_CREDENTIALS
 101         if (cred->magic != CRED_MAGIC_DEAD ||
 102             atomic_read(&cred->usage) != 0 ||
 103             read_cred_subscribers(cred) != 0)
 104                 panic("CRED: put_cred_rcu() sees %p with"
 105                       " mag %x, put %p, usage %d, subscr %d\n",
 106                       cred, cred->magic, cred->put_addr,
 107                       atomic_read(&cred->usage),
 108                       read_cred_subscribers(cred));
 109 #else
 110         if (atomic_read(&cred->usage) != 0)
 111                 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
 112                       cred, atomic_read(&cred->usage));
 113 #endif
 114
 115         security_cred_free(cred);
 116         key_put(cred->session_keyring);
 117         key_put(cred->process_keyring);
 118         key_put(cred->thread_keyring);
 119         key_put(cred->request_key_auth);
 120         if (cred->group_info)
 121                 put_group_info(cred->group_info);
 122         free_uid(cred->user);
 123         if (cred->ucounts)
 124                 put_ucounts(cred->ucounts);
 125         put_user_ns(cred->user_ns);
 126         kmem_cache_free(cred_jar, cred);
 127 }
 128
 129 /**
 130  * __put_cred - Destroy a set of credentials
 131  * @cred: The record to release
 132  *
 133  * Destroy a set of credentials on which no references remain.
 134  */
 135 void __put_cred(struct cred *cred)
 136 {
 137         kdebug("__put_cred(%p{%d,%d})", cred,
 138                atomic_read(&cred->usage),
 139                read_cred_subscribers(cred));
 140
 141         BUG_ON(atomic_read(&cred->usage) != 0);
 142 #ifdef CONFIG_DEBUG_CREDENTIALS
 143         BUG_ON(read_cred_subscribers(cred) != 0);
 144         cred->magic = CRED_MAGIC_DEAD;
 145         cred->put_addr = __builtin_return_address(0);
 146 #endif
 147         BUG_ON(cred == current->cred);
 148         BUG_ON(cred == current->real_cred);
 149
 150         if (cred->non_rcu)
 151                 put_cred_rcu(&cred->rcu);
 152         else
 153                 call_rcu(&cred->rcu, put_cred_rcu);
 154 }
 155 EXPORT_SYMBOL(__put_cred);
 156
 157 /*
 158  * Clean up a task's credentials when it exits
 159  */
 160 void exit_creds(struct task_struct *tsk)
 161 {
 162         struct cred *cred;
 163
 164         kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
 165                atomic_read(&tsk->cred->usage),
 166                read_cred_subscribers(tsk->cred));
 167
 168         cred = (struct cred *) tsk->real_cred;
 169         tsk->real_cred = NULL;
 170         validate_creds(cred);
 171         alter_cred_subscribers(cred, -1);
 172         put_cred(cred);
 173
 174         cred = (struct cred *) tsk->cred;
 175         tsk->cred = NULL;
 176         validate_creds(cred);
 177         alter_cred_subscribers(cred, -1);
 178         put_cred(cred);
 179
 180 #ifdef CONFIG_KEYS_REQUEST_CACHE
 181         key_put(tsk->cached_requested_key);
 182         tsk->cached_requested_key = NULL;
 183 #endif
 184 }
 185
 186 /**
 187  * get_task_cred - Get another task's objective credentials
 188  * @task: The task to query
 189  *
 190  * Get the objective credentials of a task, pinning them so that they can't go
 191  * away.  Accessing a task's credentials directly is not permitted.
 192  *
 193  * The caller must also make sure task doesn't get deleted, either by holding a
 194  * ref on task or by holding tasklist_lock to prevent it from being unlinked.
 195  */
 196 const struct cred *get_task_cred(struct task_struct *task)
 197 {
 198         const struct cred *cred;
 199
 200         rcu_read_lock();
 201
 202         do {
 203                 cred = __task_cred((task));
 204                 BUG_ON(!cred);
 205         } while (!get_cred_rcu(cred));
 206
 207         rcu_read_unlock();
 208         return cred;
 209 }
 210 EXPORT_SYMBOL(get_task_cred);
 211
 212 /*
 213  * Allocate blank credentials, such that the credentials can be filled in at a
 214  * later date without risk of ENOMEM.
 215  */
 216 struct cred *cred_alloc_blank(void)
 217 {
 218         struct cred *new;
 219
 220         new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
 221         if (!new)
 222                 return NULL;
 223
 224         atomic_set(&new->usage, 1);
 225 #ifdef CONFIG_DEBUG_CREDENTIALS
 226         new->magic = CRED_MAGIC;
 227 #endif
 228         new->ucounts = get_ucounts(&init_ucounts);
 229
 230         if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
 231                 goto error;
 232
 233         return new;
 234
 235 error:
 236         abort_creds(new);
 237         return NULL;
 238 }
 239
 240 /**
 241  * prepare_creds - Prepare a new set of credentials for modification
 242  *
 243  * Prepare a new set of task credentials for modification.  A task's creds
 244  * shouldn't generally be modified directly, therefore this function is used to
 245  * prepare a new copy, which the caller then modifies and then commits by
 246  * calling commit_creds().
 247  *
 248  * Preparation involves making a copy of the objective creds for modification.
 249  *
 250  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
 251  *
 252  * Call commit_creds() or abort_creds() to clean up.
 253  */
 254 struct cred *prepare_creds(void)
 255 {
 256         struct task_struct *task = current;
 257         const struct cred *old;
 258         struct cred *new;
 259
 260         validate_process_creds();
 261
 262         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 263         if (!new)
 264                 return NULL;
 265
 266         kdebug("prepare_creds() alloc %p", new);
 267
 268         old = task->cred;
 269         memcpy(new, old, sizeof(struct cred));
 270
 271         new->non_rcu = 0;
 272         atomic_set(&new->usage, 1);
 273         set_cred_subscribers(new, 0);
 274         get_group_info(new->group_info);
 275         get_uid(new->user);
 276         get_user_ns(new->user_ns);
 277
 278 #ifdef CONFIG_KEYS
 279         key_get(new->session_keyring);
 280         key_get(new->process_keyring);
 281         key_get(new->thread_keyring);
 282         key_get(new->request_key_auth);
 283 #endif
 284
 285 #ifdef CONFIG_SECURITY
 286         new->security = NULL;
 287 #endif
 288
 289         if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
 290                 goto error;
 291
 292         new->ucounts = get_ucounts(new->ucounts);
 293         if (!new->ucounts)
 294                 goto error;
 295
 296         validate_creds(new);
 297         return new;
 298
 299 error:
 300         abort_creds(new);
 301         return NULL;
 302 }
 303 EXPORT_SYMBOL(prepare_creds);
 304
 305 /*
 306  * Prepare credentials for current to perform an execve()
 307  * - The caller must hold ->cred_guard_mutex
 308  */
 309 struct cred *prepare_exec_creds(void)
 310 {
 311         struct cred *new;
 312
 313         new = prepare_creds();
 314         if (!new)
 315                 return new;
 316
 317 #ifdef CONFIG_KEYS
 318         /* newly exec'd tasks don't get a thread keyring */
 319         key_put(new->thread_keyring);
 320         new->thread_keyring = NULL;
 321
 322         /* inherit the session keyring; new process keyring */
 323         key_put(new->process_keyring);
 324         new->process_keyring = NULL;
 325 #endif
 326
 327         new->suid = new->fsuid = new->euid;
 328         new->sgid = new->fsgid = new->egid;
 329
 330         return new;
 331 }
 332
 333 /*
 334  * Copy credentials for the new process created by fork()
 335  *
 336  * We share if we can, but under some circumstances we have to generate a new
 337  * set.
 338  *
 339  * The new process gets the current process's subjective credentials as its
 340  * objective and subjective credentials
 341  */
 342 int copy_creds(struct task_struct *p, unsigned long clone_flags)
 343 {
 344         struct cred *new;
 345         int ret;
 346
 347 #ifdef CONFIG_KEYS_REQUEST_CACHE
 348         p->cached_requested_key = NULL;
 349 #endif
 350
 351         if (
 352 #ifdef CONFIG_KEYS
 353                 !p->cred->thread_keyring &&
 354 #endif
 355                 clone_flags & CLONE_THREAD
 356             ) {
 357                 p->real_cred = get_cred(p->cred);
 358                 get_cred(p->cred);
 359                 alter_cred_subscribers(p->cred, 2);
 360                 kdebug("share_creds(%p{%d,%d})",
 361                        p->cred, atomic_read(&p->cred->usage),
 362                        read_cred_subscribers(p->cred));
 363                 inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 364                 return 0;
 365         }
 366
 367         new = prepare_creds();
 368         if (!new)
 369                 return -ENOMEM;
 370
 371         if (clone_flags & CLONE_NEWUSER) {
 372                 ret = create_user_ns(new);
 373                 if (ret < 0)
 374                         goto error_put;
 375                 ret = set_cred_ucounts(new);
 376                 if (ret < 0)
 377                         goto error_put;
 378         }
 379
 380 #ifdef CONFIG_KEYS
 381         /* new threads get their own thread keyrings if their parent already
 382          * had one */
 383         if (new->thread_keyring) {
 384                 key_put(new->thread_keyring);
 385                 new->thread_keyring = NULL;
 386                 if (clone_flags & CLONE_THREAD)
 387                         install_thread_keyring_to_cred(new);
 388         }
 389
 390         /* The process keyring is only shared between the threads in a process;
 391          * anything outside of those threads doesn't inherit.
 392          */
 393         if (!(clone_flags & CLONE_THREAD)) {
 394                 key_put(new->process_keyring);
 395                 new->process_keyring = NULL;
 396         }
 397 #endif
 398
 399         p->cred = p->real_cred = get_cred(new);
 400         inc_rlimit_ucounts(task_ucounts(p), UCOUNT_RLIMIT_NPROC, 1);
 401         alter_cred_subscribers(new, 2);
 402         validate_creds(new);
 403         return 0;
 404
 405 error_put:
 406         put_cred(new);
 407         return ret;
 408 }
 409
 410 static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
 411 {
 412         const struct user_namespace *set_ns = set->user_ns;
 413         const struct user_namespace *subset_ns = subset->user_ns;
 414
 415         /* If the two credentials are in the same user namespace see if
 416          * the capabilities of subset are a subset of set.
 417          */
 418         if (set_ns == subset_ns)
 419                 return cap_issubset(subset->cap_permitted, set->cap_permitted);
 420
 421         /* The credentials are in a different user namespaces
 422          * therefore one is a subset of the other only if a set is an
 423          * ancestor of subset and set->euid is owner of subset or one
 424          * of subsets ancestors.
 425          */
 426         for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
 427                 if ((set_ns == subset_ns->parent)  &&
 428                     uid_eq(subset_ns->owner, set->euid))
 429                         return true;
 430         }
 431
 432         return false;
 433 }
 434
 435 /**
 436  * commit_creds - Install new credentials upon the current task
 437  * @new: The credentials to be assigned
 438  *
 439  * Install a new set of credentials to the current task, using RCU to replace
 440  * the old set.  Both the objective and the subjective credentials pointers are
 441  * updated.  This function may not be called if the subjective credentials are
 442  * in an overridden state.
 443  *
 444  * This function eats the caller's reference to the new credentials.
 445  *
 446  * Always returns 0 thus allowing this function to be tail-called at the end
 447  * of, say, sys_setgid().
 448  */
 449 int commit_creds(struct cred *new)
 450 {
 451         struct task_struct *task = current;
 452         const struct cred *old = task->real_cred;
 453
 454         kdebug("commit_creds(%p{%d,%d})", new,
 455                atomic_read(&new->usage),
 456                read_cred_subscribers(new));
 457
 458         BUG_ON(task->cred != old);
 459 #ifdef CONFIG_DEBUG_CREDENTIALS
 460         BUG_ON(read_cred_subscribers(old) < 2);
 461         validate_creds(old);
 462         validate_creds(new);
 463 #endif
 464         BUG_ON(atomic_read(&new->usage) < 1);
 465
 466         get_cred(new); /* we will require a ref for the subj creds too */
 467
 468         /* dumpability changes */
 469         if (!uid_eq(old->euid, new->euid) ||
 470             !gid_eq(old->egid, new->egid) ||
 471             !uid_eq(old->fsuid, new->fsuid) ||
 472             !gid_eq(old->fsgid, new->fsgid) ||
 473             !cred_cap_issubset(old, new)) {
 474                 if (task->mm)
 475                         set_dumpable(task->mm, suid_dumpable);
 476                 task->pdeath_signal = 0;
 477                 /*
 478                  * If a task drops privileges and becomes nondumpable,
 479                  * the dumpability change must become visible before
 480                  * the credential change; otherwise, a __ptrace_may_access()
 481                  * racing with this change may be able to attach to a task it
 482                  * shouldn't be able to attach to (as if the task had dropped
 483                  * privileges without becoming nondumpable).
 484                  * Pairs with a read barrier in __ptrace_may_access().
 485                  */
 486                 smp_wmb();
 487         }
 488
 489         /* alter the thread keyring */
 490         if (!uid_eq(new->fsuid, old->fsuid))
 491                 key_fsuid_changed(new);
 492         if (!gid_eq(new->fsgid, old->fsgid))
 493                 key_fsgid_changed(new);
 494
 495         /* do it
 496          * RLIMIT_NPROC limits on user->processes have already been checked
 497          * in set_user().
 498          */
 499         alter_cred_subscribers(new, 2);
 500         if (new->user != old->user || new->user_ns != old->user_ns)
 501                 inc_rlimit_ucounts(new->ucounts, UCOUNT_RLIMIT_NPROC, 1);
 502         rcu_assign_pointer(task->real_cred, new);
 503         rcu_assign_pointer(task->cred, new);
 504         if (new->user != old->user)
 505                 dec_rlimit_ucounts(old->ucounts, UCOUNT_RLIMIT_NPROC, 1);
 506         alter_cred_subscribers(old, -2);
 507
 508         /* send notifications */
 509         if (!uid_eq(new->uid,   old->uid)  ||
 510             !uid_eq(new->euid,  old->euid) ||
 511             !uid_eq(new->suid,  old->suid) ||
 512             !uid_eq(new->fsuid, old->fsuid))
 513                 proc_id_connector(task, PROC_EVENT_UID);
 514
 515         if (!gid_eq(new->gid,   old->gid)  ||
 516             !gid_eq(new->egid,  old->egid) ||
 517             !gid_eq(new->sgid,  old->sgid) ||
 518             !gid_eq(new->fsgid, old->fsgid))
 519                 proc_id_connector(task, PROC_EVENT_GID);
 520
 521         /* release the old obj and subj refs both */
 522         put_cred(old);
 523         put_cred(old);
 524         return 0;
 525 }
 526 EXPORT_SYMBOL(commit_creds);
 527
 528 /**
 529  * abort_creds - Discard a set of credentials and unlock the current task
 530  * @new: The credentials that were going to be applied
 531  *
 532  * Discard a set of credentials that were under construction and unlock the
 533  * current task.
 534  */
 535 void abort_creds(struct cred *new)
 536 {
 537         kdebug("abort_creds(%p{%d,%d})", new,
 538                atomic_read(&new->usage),
 539                read_cred_subscribers(new));
 540
 541 #ifdef CONFIG_DEBUG_CREDENTIALS
 542         BUG_ON(read_cred_subscribers(new) != 0);
 543 #endif
 544         BUG_ON(atomic_read(&new->usage) < 1);
 545         put_cred(new);
 546 }
 547 EXPORT_SYMBOL(abort_creds);
 548
 549 /**
 550  * override_creds - Override the current process's subjective credentials
 551  * @new: The credentials to be assigned
 552  *
 553  * Install a set of temporary override subjective credentials on the current
 554  * process, returning the old set for later reversion.
 555  */
 556 const struct cred *override_creds(const struct cred *new)
 557 {
 558         const struct cred *old = current->cred;
 559
 560         kdebug("override_creds(%p{%d,%d})", new,
 561                atomic_read(&new->usage),
 562                read_cred_subscribers(new));
 563
 564         validate_creds(old);
 565         validate_creds(new);
 566
 567         /*
 568          * NOTE! This uses 'get_new_cred()' rather than 'get_cred()'.
 569          *
 570          * That means that we do not clear the 'non_rcu' flag, since
 571          * we are only installing the cred into the thread-synchronous
 572          * '->cred' pointer, not the '->real_cred' pointer that is
 573          * visible to other threads under RCU.
 574          *
 575          * Also note that we did validate_creds() manually, not depending
 576          * on the validation in 'get_cred()'.
 577          */
 578         get_new_cred((struct cred *)new);
 579         alter_cred_subscribers(new, 1);
 580         rcu_assign_pointer(current->cred, new);
 581         alter_cred_subscribers(old, -1);
 582
 583         kdebug("override_creds() = %p{%d,%d}", old,
 584                atomic_read(&old->usage),
 585                read_cred_subscribers(old));
 586         return old;
 587 }
 588 EXPORT_SYMBOL(override_creds);
 589
 590 /**
 591  * revert_creds - Revert a temporary subjective credentials override
 592  * @old: The credentials to be restored
 593  *
 594  * Revert a temporary set of override subjective credentials to an old set,
 595  * discarding the override set.
 596  */
 597 void revert_creds(const struct cred *old)
 598 {
 599         const struct cred *override = current->cred;
 600
 601         kdebug("revert_creds(%p{%d,%d})", old,
 602                atomic_read(&old->usage),
 603                read_cred_subscribers(old));
 604
 605         validate_creds(old);
 606         validate_creds(override);
 607         alter_cred_subscribers(old, 1);
 608         rcu_assign_pointer(current->cred, old);
 609         alter_cred_subscribers(override, -1);
 610         put_cred(override);
 611 }
 612 EXPORT_SYMBOL(revert_creds);
 613
 614 /**
 615  * cred_fscmp - Compare two credentials with respect to filesystem access.
 616  * @a: The first credential
 617  * @b: The second credential
 618  *
 619  * cred_cmp() will return zero if both credentials have the same
 620  * fsuid, fsgid, and supplementary groups.  That is, if they will both
 621  * provide the same access to files based on mode/uid/gid.
 622  * If the credentials are different, then either -1 or 1 will
 623  * be returned depending on whether @a comes before or after @b
 624  * respectively in an arbitrary, but stable, ordering of credentials.
 625  *
 626  * Return: -1, 0, or 1 depending on comparison
 627  */
 628 int cred_fscmp(const struct cred *a, const struct cred *b)
 629 {
 630         struct group_info *ga, *gb;
 631         int g;
 632
 633         if (a == b)
 634                 return 0;
 635         if (uid_lt(a->fsuid, b->fsuid))
 636                 return -1;
 637         if (uid_gt(a->fsuid, b->fsuid))
 638                 return 1;
 639
 640         if (gid_lt(a->fsgid, b->fsgid))
 641                 return -1;
 642         if (gid_gt(a->fsgid, b->fsgid))
 643                 return 1;
 644
 645         ga = a->group_info;
 646         gb = b->group_info;
 647         if (ga == gb)
 648                 return 0;
 649         if (ga == NULL)
 650                 return -1;
 651         if (gb == NULL)
 652                 return 1;
 653         if (ga->ngroups < gb->ngroups)
 654                 return -1;
 655         if (ga->ngroups > gb->ngroups)
 656                 return 1;
 657
 658         for (g = 0; g < ga->ngroups; g++) {
 659                 if (gid_lt(ga->gid[g], gb->gid[g]))
 660                         return -1;
 661                 if (gid_gt(ga->gid[g], gb->gid[g]))
 662                         return 1;
 663         }
 664         return 0;
 665 }
 666 EXPORT_SYMBOL(cred_fscmp);
 667
 668 int set_cred_ucounts(struct cred *new)
 669 {
 670         struct task_struct *task = current;
 671         const struct cred *old = task->real_cred;
 672         struct ucounts *old_ucounts = new->ucounts;
 673
 674         if (new->user == old->user && new->user_ns == old->user_ns)
 675                 return 0;
 676
 677         /*
 678          * This optimization is needed because alloc_ucounts() uses locks
 679          * for table lookups.
 680          */
 681         if (old_ucounts && old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
 682                 return 0;
 683
 684         if (!(new->ucounts = alloc_ucounts(new->user_ns, new->euid)))
 685                 return -EAGAIN;
 686
 687         if (old_ucounts)
 688                 put_ucounts(old_ucounts);
 689
 690         return 0;
 691 }
 692
 693 /*
 694  * initialise the credentials stuff
 695  */
 696 void __init cred_init(void)
 697 {
 698         /* allocate a slab in which we can store credentials */
 699         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred), 0,
 700                         SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
 701 }
 702
 703 /**
 704  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
 705  * @daemon: A userspace daemon to be used as a reference
 706  *
 707  * Prepare a set of credentials for a kernel service.  This can then be used to
 708  * override a task's own credentials so that work can be done on behalf of that
 709  * task that requires a different subjective context.
 710  *
 711  * @daemon is used to provide a base for the security record, but can be NULL.
 712  * If @daemon is supplied, then the security data will be derived from that;
 713  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
 714  *
 715  * The caller may change these controls afterwards if desired.
 716  *
 717  * Returns the new credentials or NULL if out of memory.
 718  */
 719 struct cred *prepare_kernel_cred(struct task_struct *daemon)
 720 {
 721         const struct cred *old;
 722         struct cred *new;
 723
 724         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 725         if (!new)
 726                 return NULL;
 727
 728         kdebug("prepare_kernel_cred() alloc %p", new);
 729
 730         if (daemon)
 731                 old = get_task_cred(daemon);
 732         else
 733                 old = get_cred(&init_cred);
 734
 735         validate_creds(old);
 736
 737         *new = *old;
 738         new->non_rcu = 0;
 739         atomic_set(&new->usage, 1);
 740         set_cred_subscribers(new, 0);
 741         get_uid(new->user);
 742         get_user_ns(new->user_ns);
 743         get_group_info(new->group_info);
 744
 745 #ifdef CONFIG_KEYS
 746         new->session_keyring = NULL;
 747         new->process_keyring = NULL;
 748         new->thread_keyring = NULL;
 749         new->request_key_auth = NULL;
 750         new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 751 #endif
 752
 753 #ifdef CONFIG_SECURITY
 754         new->security = NULL;
 755 #endif
 756         if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
 757                 goto error;
 758
 759         new->ucounts = get_ucounts(new->ucounts);
 760         if (!new->ucounts)
 761                 goto error;
 762
 763         put_cred(old);
 764         validate_creds(new);
 765         return new;
 766
 767 error:
 768         put_cred(new);
 769         put_cred(old);
 770         return NULL;
 771 }
 772 EXPORT_SYMBOL(prepare_kernel_cred);
 773
 774 /**
 775  * set_security_override - Set the security ID in a set of credentials
 776  * @new: The credentials to alter
 777  * @secid: The LSM security ID to set
 778  *
 779  * Set the LSM security ID in a set of credentials so that the subjective
 780  * security is overridden when an alternative set of credentials is used.
 781  */
 782 int set_security_override(struct cred *new, u32 secid)
 783 {
 784         return security_kernel_act_as(new, secid);
 785 }
 786 EXPORT_SYMBOL(set_security_override);
 787
 788 /**
 789  * set_security_override_from_ctx - Set the security ID in a set of credentials
 790  * @new: The credentials to alter
 791  * @secctx: The LSM security context to generate the security ID from.
 792  *
 793  * Set the LSM security ID in a set of credentials so that the subjective
 794  * security is overridden when an alternative set of credentials is used.  The
 795  * security ID is specified in string form as a security context to be
 796  * interpreted by the LSM.
 797  */
 798 int set_security_override_from_ctx(struct cred *new, const char *secctx)
 799 {
 800         u32 secid;
 801         int ret;
 802
 803         ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
 804         if (ret < 0)
 805                 return ret;
 806
 807         return set_security_override(new, secid);
 808 }
 809 EXPORT_SYMBOL(set_security_override_from_ctx);
 810
 811 /**
 812  * set_create_files_as - Set the LSM file create context in a set of credentials
 813  * @new: The credentials to alter
 814  * @inode: The inode to take the context from
 815  *
 816  * Change the LSM file creation context in a set of credentials to be the same
 817  * as the object context of the specified inode, so that the new inodes have
 818  * the same MAC context as that inode.
 819  */
 820 int set_create_files_as(struct cred *new, struct inode *inode)
 821 {
 822         if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid))
 823                 return -EINVAL;
 824         new->fsuid = inode->i_uid;
 825         new->fsgid = inode->i_gid;
 826         return security_kernel_create_files_as(new, inode);
 827 }
 828 EXPORT_SYMBOL(set_create_files_as);
 829
 830 #ifdef CONFIG_DEBUG_CREDENTIALS
 831
 832 bool creds_are_invalid(const struct cred *cred)
 833 {
 834         if (cred->magic != CRED_MAGIC)
 835                 return true;
 836         return false;
 837 }
 838 EXPORT_SYMBOL(creds_are_invalid);
 839
 840 /*
 841  * dump invalid credentials
 842  */
 843 static void dump_invalid_creds(const struct cred *cred, const char *label,
 844                                const struct task_struct *tsk)
 845 {
 846         printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
 847                label, cred,
 848                cred == &init_cred ? "[init]" : "",
 849                cred == tsk->real_cred ? "[real]" : "",
 850                cred == tsk->cred ? "[eff]" : "");
 851         printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
 852                cred->magic, cred->put_addr);
 853         printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
 854                atomic_read(&cred->usage),
 855                read_cred_subscribers(cred));
 856         printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
 857                 from_kuid_munged(&init_user_ns, cred->uid),
 858                 from_kuid_munged(&init_user_ns, cred->euid),
 859                 from_kuid_munged(&init_user_ns, cred->suid),
 860                 from_kuid_munged(&init_user_ns, cred->fsuid));
 861         printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
 862                 from_kgid_munged(&init_user_ns, cred->gid),
 863                 from_kgid_munged(&init_user_ns, cred->egid),
 864                 from_kgid_munged(&init_user_ns, cred->sgid),
 865                 from_kgid_munged(&init_user_ns, cred->fsgid));
 866 #ifdef CONFIG_SECURITY
 867         printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
 868         if ((unsigned long) cred->security >= PAGE_SIZE &&
 869             (((unsigned long) cred->security & 0xffffff00) !=
 870              (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
 871                 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
 872                        ((u32*)cred->security)[0],
 873                        ((u32*)cred->security)[1]);
 874 #endif
 875 }
 876
 877 /*
 878  * report use of invalid credentials
 879  */
 880 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
 881 {
 882         printk(KERN_ERR "CRED: Invalid credentials\n");
 883         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 884         dump_invalid_creds(cred, "Specified", current);
 885         BUG();
 886 }
 887 EXPORT_SYMBOL(__invalid_creds);
 888
 889 /*
 890  * check the credentials on a process
 891  */
 892 void __validate_process_creds(struct task_struct *tsk,
 893                               const char *file, unsigned line)
 894 {
 895         if (tsk->cred == tsk->real_cred) {
 896                 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
 897                              creds_are_invalid(tsk->cred)))
 898                         goto invalid_creds;
 899         } else {
 900                 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
 901                              read_cred_subscribers(tsk->cred) < 1 ||
 902                              creds_are_invalid(tsk->real_cred) ||
 903                              creds_are_invalid(tsk->cred)))
 904                         goto invalid_creds;
 905         }
 906         return;
 907
 908 invalid_creds:
 909         printk(KERN_ERR "CRED: Invalid process credentials\n");
 910         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 911
 912         dump_invalid_creds(tsk->real_cred, "Real", tsk);
 913         if (tsk->cred != tsk->real_cred)
 914                 dump_invalid_creds(tsk->cred, "Effective", tsk);
 915         else
 916                 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
 917         BUG();
 918 }
 919 EXPORT_SYMBOL(__validate_process_creds);
 920
 921 /*
 922  * check creds for do_exit()
 923  */
 924 void validate_creds_for_do_exit(struct task_struct *tsk)
 925 {
 926         kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
 927                tsk->real_cred, tsk->cred,
 928                atomic_read(&tsk->cred->usage),
 929                read_cred_subscribers(tsk->cred));
 930
 931         __validate_process_creds(tsk, __FILE__, __LINE__);
 932 }
 933
 934 #endif /* CONFIG_DEBUG_CREDENTIALS */