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