kernel/cred.c

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