kernel/cred.c

   1 /* Task credentials management - see Documentation/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/module.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/cn_proc.h>
  20
  21 #if 0
  22 #define kdebug(FMT, ...) \
  23         printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
  24 #else
  25 #define kdebug(FMT, ...) \
  26         no_printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
  27 #endif
  28
  29 static struct kmem_cache *cred_jar;
  30
  31 /*
  32  * The common credentials for the initial task's thread group
  33  */
  34 #ifdef CONFIG_KEYS
  35 static struct thread_group_cred init_tgcred = {
  36         .usage  = ATOMIC_INIT(2),
  37         .tgid   = 0,
  38         .lock   = __SPIN_LOCK_UNLOCKED(init_cred.tgcred.lock),
  39 };
  40 #endif
  41
  42 /*
  43  * The initial credentials for the initial task
  44  */
  45 struct cred init_cred = {
  46         .usage                  = ATOMIC_INIT(4),
  47 #ifdef CONFIG_DEBUG_CREDENTIALS
  48         .subscribers            = ATOMIC_INIT(2),
  49         .magic                  = CRED_MAGIC,
  50 #endif
  51         .securebits             = SECUREBITS_DEFAULT,
  52         .cap_inheritable        = CAP_INIT_INH_SET,
  53         .cap_permitted          = CAP_FULL_SET,
  54         .cap_effective          = CAP_INIT_EFF_SET,
  55         .cap_bset               = CAP_INIT_BSET,
  56         .user                   = INIT_USER,
  57         .group_info             = &init_groups,
  58 #ifdef CONFIG_KEYS
  59         .tgcred                 = &init_tgcred,
  60 #endif
  61 };
  62
  63 static inline void set_cred_subscribers(struct cred *cred, int n)
  64 {
  65 #ifdef CONFIG_DEBUG_CREDENTIALS
  66         atomic_set(&cred->subscribers, n);
  67 #endif
  68 }
  69
  70 static inline int read_cred_subscribers(const struct cred *cred)
  71 {
  72 #ifdef CONFIG_DEBUG_CREDENTIALS
  73         return atomic_read(&cred->subscribers);
  74 #else
  75         return 0;
  76 #endif
  77 }
  78
  79 static inline void alter_cred_subscribers(const struct cred *_cred, int n)
  80 {
  81 #ifdef CONFIG_DEBUG_CREDENTIALS
  82         struct cred *cred = (struct cred *) _cred;
  83
  84         atomic_add(n, &cred->subscribers);
  85 #endif
  86 }
  87
  88 /*
  89  * Dispose of the shared task group credentials
  90  */
  91 #ifdef CONFIG_KEYS
  92 static void release_tgcred_rcu(struct rcu_head *rcu)
  93 {
  94         struct thread_group_cred *tgcred =
  95                 container_of(rcu, struct thread_group_cred, rcu);
  96
  97         BUG_ON(atomic_read(&tgcred->usage) != 0);
  98
  99         key_put(tgcred->session_keyring);
 100         key_put(tgcred->process_keyring);
 101         kfree(tgcred);
 102 }
 103 #endif
 104
 105 /*
 106  * Release a set of thread group credentials.
 107  */
 108 static void release_tgcred(struct cred *cred)
 109 {
 110 #ifdef CONFIG_KEYS
 111         struct thread_group_cred *tgcred = cred->tgcred;
 112
 113         if (atomic_dec_and_test(&tgcred->usage))
 114                 call_rcu(&tgcred->rcu, release_tgcred_rcu);
 115 #endif
 116 }
 117
 118 /*
 119  * The RCU callback to actually dispose of a set of credentials
 120  */
 121 static void put_cred_rcu(struct rcu_head *rcu)
 122 {
 123         struct cred *cred = container_of(rcu, struct cred, rcu);
 124
 125         kdebug("put_cred_rcu(%p)", cred);
 126
 127 #ifdef CONFIG_DEBUG_CREDENTIALS
 128         if (cred->magic != CRED_MAGIC_DEAD ||
 129             atomic_read(&cred->usage) != 0 ||
 130             read_cred_subscribers(cred) != 0)
 131                 panic("CRED: put_cred_rcu() sees %p with"
 132                       " mag %x, put %p, usage %d, subscr %d\n",
 133                       cred, cred->magic, cred->put_addr,
 134                       atomic_read(&cred->usage),
 135                       read_cred_subscribers(cred));
 136 #else
 137         if (atomic_read(&cred->usage) != 0)
 138                 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
 139                       cred, atomic_read(&cred->usage));
 140 #endif
 141
 142         security_cred_free(cred);
 143         key_put(cred->thread_keyring);
 144         key_put(cred->request_key_auth);
 145         release_tgcred(cred);
 146         if (cred->group_info)
 147                 put_group_info(cred->group_info);
 148         free_uid(cred->user);
 149         kmem_cache_free(cred_jar, cred);
 150 }
 151
 152 /**
 153  * __put_cred - Destroy a set of credentials
 154  * @cred: The record to release
 155  *
 156  * Destroy a set of credentials on which no references remain.
 157  */
 158 void __put_cred(struct cred *cred)
 159 {
 160         kdebug("__put_cred(%p{%d,%d})", cred,
 161                atomic_read(&cred->usage),
 162                read_cred_subscribers(cred));
 163
 164         BUG_ON(atomic_read(&cred->usage) != 0);
 165 #ifdef CONFIG_DEBUG_CREDENTIALS
 166         BUG_ON(read_cred_subscribers(cred) != 0);
 167         cred->magic = CRED_MAGIC_DEAD;
 168         cred->put_addr = __builtin_return_address(0);
 169 #endif
 170         BUG_ON(cred == current->cred);
 171         BUG_ON(cred == current->real_cred);
 172
 173         call_rcu(&cred->rcu, put_cred_rcu);
 174 }
 175 EXPORT_SYMBOL(__put_cred);
 176
 177 /*
 178  * Clean up a task's credentials when it exits
 179  */
 180 void exit_creds(struct task_struct *tsk)
 181 {
 182         struct cred *cred;
 183
 184         kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
 185                atomic_read(&tsk->cred->usage),
 186                read_cred_subscribers(tsk->cred));
 187
 188         cred = (struct cred *) tsk->real_cred;
 189         tsk->real_cred = NULL;
 190         validate_creds(cred);
 191         alter_cred_subscribers(cred, -1);
 192         put_cred(cred);
 193
 194         cred = (struct cred *) tsk->cred;
 195         tsk->cred = NULL;
 196         validate_creds(cred);
 197         alter_cred_subscribers(cred, -1);
 198         put_cred(cred);
 199
 200         cred = (struct cred *) tsk->replacement_session_keyring;
 201         if (cred) {
 202                 tsk->replacement_session_keyring = NULL;
 203                 validate_creds(cred);
 204                 put_cred(cred);
 205         }
 206 }
 207
 208 /**
 209  * get_task_cred - Get another task's objective credentials
 210  * @task: The task to query
 211  *
 212  * Get the objective credentials of a task, pinning them so that they can't go
 213  * away.  Accessing a task's credentials directly is not permitted.
 214  *
 215  * The caller must also make sure task doesn't get deleted, either by holding a
 216  * ref on task or by holding tasklist_lock to prevent it from being unlinked.
 217  */
 218 const struct cred *get_task_cred(struct task_struct *task)
 219 {
 220         const struct cred *cred;
 221
 222         rcu_read_lock();
 223
 224         do {
 225                 cred = __task_cred((task));
 226                 BUG_ON(!cred);
 227         } while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));
 228
 229         rcu_read_unlock();
 230         return cred;
 231 }
 232
 233 /*
 234  * Allocate blank credentials, such that the credentials can be filled in at a
 235  * later date without risk of ENOMEM.
 236  */
 237 struct cred *cred_alloc_blank(void)
 238 {
 239         struct cred *new;
 240
 241         new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
 242         if (!new)
 243                 return NULL;
 244
 245 #ifdef CONFIG_KEYS
 246         new->tgcred = kzalloc(sizeof(*new->tgcred), GFP_KERNEL);
 247         if (!new->tgcred) {
 248                 kmem_cache_free(cred_jar, new);
 249                 return NULL;
 250         }
 251         atomic_set(&new->tgcred->usage, 1);
 252 #endif
 253
 254         atomic_set(&new->usage, 1);
 255 #ifdef CONFIG_DEBUG_CREDENTIALS
 256         new->magic = CRED_MAGIC;
 257 #endif
 258
 259         if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
 260                 goto error;
 261
 262         return new;
 263
 264 error:
 265         abort_creds(new);
 266         return NULL;
 267 }
 268
 269 /**
 270  * prepare_creds - Prepare a new set of credentials for modification
 271  *
 272  * Prepare a new set of task credentials for modification.  A task's creds
 273  * shouldn't generally be modified directly, therefore this function is used to
 274  * prepare a new copy, which the caller then modifies and then commits by
 275  * calling commit_creds().
 276  *
 277  * Preparation involves making a copy of the objective creds for modification.
 278  *
 279  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
 280  *
 281  * Call commit_creds() or abort_creds() to clean up.
 282  */
 283 struct cred *prepare_creds(void)
 284 {
 285         struct task_struct *task = current;
 286         const struct cred *old;
 287         struct cred *new;
 288
 289         validate_process_creds();
 290
 291         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 292         if (!new)
 293                 return NULL;
 294
 295         kdebug("prepare_creds() alloc %p", new);
 296
 297         old = task->cred;
 298         memcpy(new, old, sizeof(struct cred));
 299
 300         atomic_set(&new->usage, 1);
 301         set_cred_subscribers(new, 0);
 302         get_group_info(new->group_info);
 303         get_uid(new->user);
 304
 305 #ifdef CONFIG_KEYS
 306         key_get(new->thread_keyring);
 307         key_get(new->request_key_auth);
 308         atomic_inc(&new->tgcred->usage);
 309 #endif
 310
 311 #ifdef CONFIG_SECURITY
 312         new->security = NULL;
 313 #endif
 314
 315         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 316                 goto error;
 317         validate_creds(new);
 318         return new;
 319
 320 error:
 321         abort_creds(new);
 322         return NULL;
 323 }
 324 EXPORT_SYMBOL(prepare_creds);
 325
 326 /*
 327  * Prepare credentials for current to perform an execve()
 328  * - The caller must hold ->cred_guard_mutex
 329  */
 330 struct cred *prepare_exec_creds(void)
 331 {
 332         struct thread_group_cred *tgcred = NULL;
 333         struct cred *new;
 334
 335 #ifdef CONFIG_KEYS
 336         tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 337         if (!tgcred)
 338                 return NULL;
 339 #endif
 340
 341         new = prepare_creds();
 342         if (!new) {
 343                 kfree(tgcred);
 344                 return new;
 345         }
 346
 347 #ifdef CONFIG_KEYS
 348         /* newly exec'd tasks don't get a thread keyring */
 349         key_put(new->thread_keyring);
 350         new->thread_keyring = NULL;
 351
 352         /* create a new per-thread-group creds for all this set of threads to
 353          * share */
 354         memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
 355
 356         atomic_set(&tgcred->usage, 1);
 357         spin_lock_init(&tgcred->lock);
 358
 359         /* inherit the session keyring; new process keyring */
 360         key_get(tgcred->session_keyring);
 361         tgcred->process_keyring = NULL;
 362
 363         release_tgcred(new);
 364         new->tgcred = tgcred;
 365 #endif
 366
 367         return new;
 368 }
 369
 370 /*
 371  * Copy credentials for the new process created by fork()
 372  *
 373  * We share if we can, but under some circumstances we have to generate a new
 374  * set.
 375  *
 376  * The new process gets the current process's subjective credentials as its
 377  * objective and subjective credentials
 378  */
 379 int copy_creds(struct task_struct *p, unsigned long clone_flags)
 380 {
 381 #ifdef CONFIG_KEYS
 382         struct thread_group_cred *tgcred;
 383 #endif
 384         struct cred *new;
 385         int ret;
 386
 387         if (
 388 #ifdef CONFIG_KEYS
 389                 !p->cred->thread_keyring &&
 390 #endif
 391                 clone_flags & CLONE_THREAD
 392             ) {
 393                 p->real_cred = get_cred(p->cred);
 394                 get_cred(p->cred);
 395                 alter_cred_subscribers(p->cred, 2);
 396                 kdebug("share_creds(%p{%d,%d})",
 397                        p->cred, atomic_read(&p->cred->usage),
 398                        read_cred_subscribers(p->cred));
 399                 atomic_inc(&p->cred->user->processes);
 400                 return 0;
 401         }
 402
 403         new = prepare_creds();
 404         if (!new)
 405                 return -ENOMEM;
 406
 407         if (clone_flags & CLONE_NEWUSER) {
 408                 ret = create_user_ns(new);
 409                 if (ret < 0)
 410                         goto error_put;
 411         }
 412
 413 #ifdef CONFIG_KEYS
 414         /* new threads get their own thread keyrings if their parent already
 415          * had one */
 416         if (new->thread_keyring) {
 417                 key_put(new->thread_keyring);
 418                 new->thread_keyring = NULL;
 419                 if (clone_flags & CLONE_THREAD)
 420                         install_thread_keyring_to_cred(new);
 421         }
 422
 423         /* we share the process and session keyrings between all the threads in
 424          * a process - this is slightly icky as we violate COW credentials a
 425          * bit */
 426         if (!(clone_flags & CLONE_THREAD)) {
 427                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 428                 if (!tgcred) {
 429                         ret = -ENOMEM;
 430                         goto error_put;
 431                 }
 432                 atomic_set(&tgcred->usage, 1);
 433                 spin_lock_init(&tgcred->lock);
 434                 tgcred->process_keyring = NULL;
 435                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
 436
 437                 release_tgcred(new);
 438                 new->tgcred = tgcred;
 439         }
 440 #endif
 441
 442         atomic_inc(&new->user->processes);
 443         p->cred = p->real_cred = get_cred(new);
 444         alter_cred_subscribers(new, 2);
 445         validate_creds(new);
 446         return 0;
 447
 448 error_put:
 449         put_cred(new);
 450         return ret;
 451 }
 452
 453 /**
 454  * commit_creds - Install new credentials upon the current task
 455  * @new: The credentials to be assigned
 456  *
 457  * Install a new set of credentials to the current task, using RCU to replace
 458  * the old set.  Both the objective and the subjective credentials pointers are
 459  * updated.  This function may not be called if the subjective credentials are
 460  * in an overridden state.
 461  *
 462  * This function eats the caller's reference to the new credentials.
 463  *
 464  * Always returns 0 thus allowing this function to be tail-called at the end
 465  * of, say, sys_setgid().
 466  */
 467 int commit_creds(struct cred *new)
 468 {
 469         struct task_struct *task = current;
 470         const struct cred *old = task->real_cred;
 471
 472         kdebug("commit_creds(%p{%d,%d})", new,
 473                atomic_read(&new->usage),
 474                read_cred_subscribers(new));
 475
 476         BUG_ON(task->cred != old);
 477 #ifdef CONFIG_DEBUG_CREDENTIALS
 478         BUG_ON(read_cred_subscribers(old) < 2);
 479         validate_creds(old);
 480         validate_creds(new);
 481 #endif
 482         BUG_ON(atomic_read(&new->usage) < 1);
 483
 484         get_cred(new); /* we will require a ref for the subj creds too */
 485
 486         /* dumpability changes */
 487         if (old->euid != new->euid ||
 488             old->egid != new->egid ||
 489             old->fsuid != new->fsuid ||
 490             old->fsgid != new->fsgid ||
 491             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
 492                 if (task->mm)
 493                         set_dumpable(task->mm, suid_dumpable);
 494                 task->pdeath_signal = 0;
 495                 smp_wmb();
 496         }
 497
 498         /* alter the thread keyring */
 499         if (new->fsuid != old->fsuid)
 500                 key_fsuid_changed(task);
 501         if (new->fsgid != old->fsgid)
 502                 key_fsgid_changed(task);
 503
 504         /* do it
 505          * - What if a process setreuid()'s and this brings the
 506          *   new uid over his NPROC rlimit?  We can check this now
 507          *   cheaply with the new uid cache, so if it matters
 508          *   we should be checking for it.  -DaveM
 509          */
 510         alter_cred_subscribers(new, 2);
 511         if (new->user != old->user)
 512                 atomic_inc(&new->user->processes);
 513         rcu_assign_pointer(task->real_cred, new);
 514         rcu_assign_pointer(task->cred, new);
 515         if (new->user != old->user)
 516                 atomic_dec(&old->user->processes);
 517         alter_cred_subscribers(old, -2);
 518
 519         /* send notifications */
 520         if (new->uid   != old->uid  ||
 521             new->euid  != old->euid ||
 522             new->suid  != old->suid ||
 523             new->fsuid != old->fsuid)
 524                 proc_id_connector(task, PROC_EVENT_UID);
 525
 526         if (new->gid   != old->gid  ||
 527             new->egid  != old->egid ||
 528             new->sgid  != old->sgid ||
 529             new->fsgid != old->fsgid)
 530                 proc_id_connector(task, PROC_EVENT_GID);
 531
 532         /* release the old obj and subj refs both */
 533         put_cred(old);
 534         put_cred(old);
 535         return 0;
 536 }
 537 EXPORT_SYMBOL(commit_creds);
 538
 539 /**
 540  * abort_creds - Discard a set of credentials and unlock the current task
 541  * @new: The credentials that were going to be applied
 542  *
 543  * Discard a set of credentials that were under construction and unlock the
 544  * current task.
 545  */
 546 void abort_creds(struct cred *new)
 547 {
 548         kdebug("abort_creds(%p{%d,%d})", new,
 549                atomic_read(&new->usage),
 550                read_cred_subscribers(new));
 551
 552 #ifdef CONFIG_DEBUG_CREDENTIALS
 553         BUG_ON(read_cred_subscribers(new) != 0);
 554 #endif
 555         BUG_ON(atomic_read(&new->usage) < 1);
 556         put_cred(new);
 557 }
 558 EXPORT_SYMBOL(abort_creds);
 559
 560 /**
 561  * override_creds - Override the current process's subjective credentials
 562  * @new: The credentials to be assigned
 563  *
 564  * Install a set of temporary override subjective credentials on the current
 565  * process, returning the old set for later reversion.
 566  */
 567 const struct cred *override_creds(const struct cred *new)
 568 {
 569         const struct cred *old = current->cred;
 570
 571         kdebug("override_creds(%p{%d,%d})", new,
 572                atomic_read(&new->usage),
 573                read_cred_subscribers(new));
 574
 575         validate_creds(old);
 576         validate_creds(new);
 577         get_cred(new);
 578         alter_cred_subscribers(new, 1);
 579         rcu_assign_pointer(current->cred, new);
 580         alter_cred_subscribers(old, -1);
 581
 582         kdebug("override_creds() = %p{%d,%d}", old,
 583                atomic_read(&old->usage),
 584                read_cred_subscribers(old));
 585         return old;
 586 }
 587 EXPORT_SYMBOL(override_creds);
 588
 589 /**
 590  * revert_creds - Revert a temporary subjective credentials override
 591  * @old: The credentials to be restored
 592  *
 593  * Revert a temporary set of override subjective credentials to an old set,
 594  * discarding the override set.
 595  */
 596 void revert_creds(const struct cred *old)
 597 {
 598         const struct cred *override = current->cred;
 599
 600         kdebug("revert_creds(%p{%d,%d})", old,
 601                atomic_read(&old->usage),
 602                read_cred_subscribers(old));
 603
 604         validate_creds(old);
 605         validate_creds(override);
 606         alter_cred_subscribers(old, 1);
 607         rcu_assign_pointer(current->cred, old);
 608         alter_cred_subscribers(override, -1);
 609         put_cred(override);
 610 }
 611 EXPORT_SYMBOL(revert_creds);
 612
 613 /*
 614  * initialise the credentials stuff
 615  */
 616 void __init cred_init(void)
 617 {
 618         /* allocate a slab in which we can store credentials */
 619         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
 620                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 621 }
 622
 623 /**
 624  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
 625  * @daemon: A userspace daemon to be used as a reference
 626  *
 627  * Prepare a set of credentials for a kernel service.  This can then be used to
 628  * override a task's own credentials so that work can be done on behalf of that
 629  * task that requires a different subjective context.
 630  *
 631  * @daemon is used to provide a base for the security record, but can be NULL.
 632  * If @daemon is supplied, then the security data will be derived from that;
 633  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
 634  *
 635  * The caller may change these controls afterwards if desired.
 636  *
 637  * Returns the new credentials or NULL if out of memory.
 638  *
 639  * Does not take, and does not return holding current->cred_replace_mutex.
 640  */
 641 struct cred *prepare_kernel_cred(struct task_struct *daemon)
 642 {
 643         const struct cred *old;
 644         struct cred *new;
 645
 646         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 647         if (!new)
 648                 return NULL;
 649
 650         kdebug("prepare_kernel_cred() alloc %p", new);
 651
 652         if (daemon)
 653                 old = get_task_cred(daemon);
 654         else
 655                 old = get_cred(&init_cred);
 656
 657         validate_creds(old);
 658
 659         *new = *old;
 660         atomic_set(&new->usage, 1);
 661         set_cred_subscribers(new, 0);
 662         get_uid(new->user);
 663         get_group_info(new->group_info);
 664
 665 #ifdef CONFIG_KEYS
 666         atomic_inc(&init_tgcred.usage);
 667         new->tgcred = &init_tgcred;
 668         new->request_key_auth = NULL;
 669         new->thread_keyring = NULL;
 670         new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 671 #endif
 672
 673 #ifdef CONFIG_SECURITY
 674         new->security = NULL;
 675 #endif
 676         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 677                 goto error;
 678
 679         put_cred(old);
 680         validate_creds(new);
 681         return new;
 682
 683 error:
 684         put_cred(new);
 685         put_cred(old);
 686         return NULL;
 687 }
 688 EXPORT_SYMBOL(prepare_kernel_cred);
 689
 690 /**
 691  * set_security_override - Set the security ID in a set of credentials
 692  * @new: The credentials to alter
 693  * @secid: The LSM security ID to set
 694  *
 695  * Set the LSM security ID in a set of credentials so that the subjective
 696  * security is overridden when an alternative set of credentials is used.
 697  */
 698 int set_security_override(struct cred *new, u32 secid)
 699 {
 700         return security_kernel_act_as(new, secid);
 701 }
 702 EXPORT_SYMBOL(set_security_override);
 703
 704 /**
 705  * set_security_override_from_ctx - Set the security ID in a set of credentials
 706  * @new: The credentials to alter
 707  * @secctx: The LSM security context to generate the security ID from.
 708  *
 709  * Set the LSM security ID in a set of credentials so that the subjective
 710  * security is overridden when an alternative set of credentials is used.  The
 711  * security ID is specified in string form as a security context to be
 712  * interpreted by the LSM.
 713  */
 714 int set_security_override_from_ctx(struct cred *new, const char *secctx)
 715 {
 716         u32 secid;
 717         int ret;
 718
 719         ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
 720         if (ret < 0)
 721                 return ret;
 722
 723         return set_security_override(new, secid);
 724 }
 725 EXPORT_SYMBOL(set_security_override_from_ctx);
 726
 727 /**
 728  * set_create_files_as - Set the LSM file create context in a set of credentials
 729  * @new: The credentials to alter
 730  * @inode: The inode to take the context from
 731  *
 732  * Change the LSM file creation context in a set of credentials to be the same
 733  * as the object context of the specified inode, so that the new inodes have
 734  * the same MAC context as that inode.
 735  */
 736 int set_create_files_as(struct cred *new, struct inode *inode)
 737 {
 738         new->fsuid = inode->i_uid;
 739         new->fsgid = inode->i_gid;
 740         return security_kernel_create_files_as(new, inode);
 741 }
 742 EXPORT_SYMBOL(set_create_files_as);
 743
 744 struct user_namespace *current_user_ns(void)
 745 {
 746         return _current_user_ns();
 747 }
 748 EXPORT_SYMBOL(current_user_ns);
 749
 750 #ifdef CONFIG_DEBUG_CREDENTIALS
 751
 752 bool creds_are_invalid(const struct cred *cred)
 753 {
 754         if (cred->magic != CRED_MAGIC)
 755                 return true;
 756 #ifdef CONFIG_SECURITY_SELINUX
 757         /*
 758          * cred->security == NULL if security_cred_alloc_blank() or
 759          * security_prepare_creds() returned an error.
 760          */
 761         if (selinux_is_enabled() && cred->security) {
 762                 if ((unsigned long) cred->security < PAGE_SIZE)
 763                         return true;
 764                 if ((*(u32 *)cred->security & 0xffffff00) ==
 765                     (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
 766                         return true;
 767         }
 768 #endif
 769         return false;
 770 }
 771 EXPORT_SYMBOL(creds_are_invalid);
 772
 773 /*
 774  * dump invalid credentials
 775  */
 776 static void dump_invalid_creds(const struct cred *cred, const char *label,
 777                                const struct task_struct *tsk)
 778 {
 779         printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
 780                label, cred,
 781                cred == &init_cred ? "[init]" : "",
 782                cred == tsk->real_cred ? "[real]" : "",
 783                cred == tsk->cred ? "[eff]" : "");
 784         printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
 785                cred->magic, cred->put_addr);
 786         printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
 787                atomic_read(&cred->usage),
 788                read_cred_subscribers(cred));
 789         printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
 790                cred->uid, cred->euid, cred->suid, cred->fsuid);
 791         printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
 792                cred->gid, cred->egid, cred->sgid, cred->fsgid);
 793 #ifdef CONFIG_SECURITY
 794         printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
 795         if ((unsigned long) cred->security >= PAGE_SIZE &&
 796             (((unsigned long) cred->security & 0xffffff00) !=
 797              (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
 798                 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
 799                        ((u32*)cred->security)[0],
 800                        ((u32*)cred->security)[1]);
 801 #endif
 802 }
 803
 804 /*
 805  * report use of invalid credentials
 806  */
 807 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
 808 {
 809         printk(KERN_ERR "CRED: Invalid credentials\n");
 810         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 811         dump_invalid_creds(cred, "Specified", current);
 812         BUG();
 813 }
 814 EXPORT_SYMBOL(__invalid_creds);
 815
 816 /*
 817  * check the credentials on a process
 818  */
 819 void __validate_process_creds(struct task_struct *tsk,
 820                               const char *file, unsigned line)
 821 {
 822         if (tsk->cred == tsk->real_cred) {
 823                 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
 824                              creds_are_invalid(tsk->cred)))
 825                         goto invalid_creds;
 826         } else {
 827                 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
 828                              read_cred_subscribers(tsk->cred) < 1 ||
 829                              creds_are_invalid(tsk->real_cred) ||
 830                              creds_are_invalid(tsk->cred)))
 831                         goto invalid_creds;
 832         }
 833         return;
 834
 835 invalid_creds:
 836         printk(KERN_ERR "CRED: Invalid process credentials\n");
 837         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 838
 839         dump_invalid_creds(tsk->real_cred, "Real", tsk);
 840         if (tsk->cred != tsk->real_cred)
 841                 dump_invalid_creds(tsk->cred, "Effective", tsk);
 842         else
 843                 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
 844         BUG();
 845 }
 846 EXPORT_SYMBOL(__validate_process_creds);
 847
 848 /*
 849  * check creds for do_exit()
 850  */
 851 void validate_creds_for_do_exit(struct task_struct *tsk)
 852 {
 853         kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
 854                tsk->real_cred, tsk->cred,
 855                atomic_read(&tsk->cred->usage),
 856                read_cred_subscribers(tsk->cred));
 857
 858         __validate_process_creds(tsk, __FILE__, __LINE__);
 859 }
 860
 861 #endif /* CONFIG_DEBUG_CREDENTIALS */