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 static inline __attribute__((format(printf, 1, 2)))
  26 void no_printk(const char *fmt, ...)
  27 {
  28 }
  29 #define kdebug(FMT, ...) \
  30         no_printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
  31 #endif
  32
  33 static struct kmem_cache *cred_jar;
  34
  35 /*
  36  * The common credentials for the initial task's thread group
  37  */
  38 #ifdef CONFIG_KEYS
  39 static struct thread_group_cred init_tgcred = {
  40         .usage  = ATOMIC_INIT(2),
  41         .tgid   = 0,
  42         .lock   = SPIN_LOCK_UNLOCKED,
  43 };
  44 #endif
  45
  46 /*
  47  * The initial credentials for the initial task
  48  */
  49 struct cred init_cred = {
  50         .usage                  = ATOMIC_INIT(4),
  51 #ifdef CONFIG_DEBUG_CREDENTIALS
  52         .subscribers            = ATOMIC_INIT(2),
  53         .magic                  = CRED_MAGIC,
  54 #endif
  55         .securebits             = SECUREBITS_DEFAULT,
  56         .cap_inheritable        = CAP_INIT_INH_SET,
  57         .cap_permitted          = CAP_FULL_SET,
  58         .cap_effective          = CAP_INIT_EFF_SET,
  59         .cap_bset               = CAP_INIT_BSET,
  60         .user                   = INIT_USER,
  61         .group_info             = &init_groups,
  62 #ifdef CONFIG_KEYS
  63         .tgcred                 = &init_tgcred,
  64 #endif
  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  * Dispose of the shared task group credentials
  94  */
  95 #ifdef CONFIG_KEYS
  96 static void release_tgcred_rcu(struct rcu_head *rcu)
  97 {
  98         struct thread_group_cred *tgcred =
  99                 container_of(rcu, struct thread_group_cred, rcu);
 100
 101         BUG_ON(atomic_read(&tgcred->usage) != 0);
 102
 103         key_put(tgcred->session_keyring);
 104         key_put(tgcred->process_keyring);
 105         kfree(tgcred);
 106 }
 107 #endif
 108
 109 /*
 110  * Release a set of thread group credentials.
 111  */
 112 static void release_tgcred(struct cred *cred)
 113 {
 114 #ifdef CONFIG_KEYS
 115         struct thread_group_cred *tgcred = cred->tgcred;
 116
 117         if (atomic_dec_and_test(&tgcred->usage))
 118                 call_rcu(&tgcred->rcu, release_tgcred_rcu);
 119 #endif
 120 }
 121
 122 /*
 123  * The RCU callback to actually dispose of a set of credentials
 124  */
 125 static void put_cred_rcu(struct rcu_head *rcu)
 126 {
 127         struct cred *cred = container_of(rcu, struct cred, rcu);
 128
 129         kdebug("put_cred_rcu(%p)", cred);
 130
 131 #ifdef CONFIG_DEBUG_CREDENTIALS
 132         if (cred->magic != CRED_MAGIC_DEAD ||
 133             atomic_read(&cred->usage) != 0 ||
 134             read_cred_subscribers(cred) != 0)
 135                 panic("CRED: put_cred_rcu() sees %p with"
 136                       " mag %x, put %p, usage %d, subscr %d\n",
 137                       cred, cred->magic, cred->put_addr,
 138                       atomic_read(&cred->usage),
 139                       read_cred_subscribers(cred));
 140 #else
 141         if (atomic_read(&cred->usage) != 0)
 142                 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
 143                       cred, atomic_read(&cred->usage));
 144 #endif
 145
 146         security_cred_free(cred);
 147         key_put(cred->thread_keyring);
 148         key_put(cred->request_key_auth);
 149         release_tgcred(cred);
 150         if (cred->group_info)
 151                 put_group_info(cred->group_info);
 152         free_uid(cred->user);
 153         kmem_cache_free(cred_jar, cred);
 154 }
 155
 156 /**
 157  * __put_cred - Destroy a set of credentials
 158  * @cred: The record to release
 159  *
 160  * Destroy a set of credentials on which no references remain.
 161  */
 162 void __put_cred(struct cred *cred)
 163 {
 164         kdebug("__put_cred(%p{%d,%d})", cred,
 165                atomic_read(&cred->usage),
 166                read_cred_subscribers(cred));
 167
 168         BUG_ON(atomic_read(&cred->usage) != 0);
 169 #ifdef CONFIG_DEBUG_CREDENTIALS
 170         BUG_ON(read_cred_subscribers(cred) != 0);
 171         cred->magic = CRED_MAGIC_DEAD;
 172         cred->put_addr = __builtin_return_address(0);
 173 #endif
 174         BUG_ON(cred == current->cred);
 175         BUG_ON(cred == current->real_cred);
 176
 177         call_rcu(&cred->rcu, put_cred_rcu);
 178 }
 179 EXPORT_SYMBOL(__put_cred);
 180
 181 /*
 182  * Clean up a task's credentials when it exits
 183  */
 184 void exit_creds(struct task_struct *tsk)
 185 {
 186         struct cred *cred;
 187
 188         kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
 189                atomic_read(&tsk->cred->usage),
 190                read_cred_subscribers(tsk->cred));
 191
 192         cred = (struct cred *) tsk->real_cred;
 193         tsk->real_cred = NULL;
 194         validate_creds(cred);
 195         alter_cred_subscribers(cred, -1);
 196         put_cred(cred);
 197
 198         cred = (struct cred *) tsk->cred;
 199         tsk->cred = NULL;
 200         validate_creds(cred);
 201         alter_cred_subscribers(cred, -1);
 202         put_cred(cred);
 203
 204         cred = (struct cred *) tsk->replacement_session_keyring;
 205         if (cred) {
 206                 tsk->replacement_session_keyring = NULL;
 207                 validate_creds(cred);
 208                 put_cred(cred);
 209         }
 210 }
 211
 212 /**
 213  * get_task_cred - Get another task's objective credentials
 214  * @task: The task to query
 215  *
 216  * Get the objective credentials of a task, pinning them so that they can't go
 217  * away.  Accessing a task's credentials directly is not permitted.
 218  *
 219  * The caller must also make sure task doesn't get deleted, either by holding a
 220  * ref on task or by holding tasklist_lock to prevent it from being unlinked.
 221  */
 222 const struct cred *get_task_cred(struct task_struct *task)
 223 {
 224         const struct cred *cred;
 225
 226         rcu_read_lock();
 227
 228         do {
 229                 cred = __task_cred((task));
 230                 BUG_ON(!cred);
 231         } while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));
 232
 233         rcu_read_unlock();
 234         return cred;
 235 }
 236
 237 /*
 238  * Allocate blank credentials, such that the credentials can be filled in at a
 239  * later date without risk of ENOMEM.
 240  */
 241 struct cred *cred_alloc_blank(void)
 242 {
 243         struct cred *new;
 244
 245         new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
 246         if (!new)
 247                 return NULL;
 248
 249 #ifdef CONFIG_KEYS
 250         new->tgcred = kzalloc(sizeof(*new->tgcred), GFP_KERNEL);
 251         if (!new->tgcred) {
 252                 kmem_cache_free(cred_jar, new);
 253                 return NULL;
 254         }
 255         atomic_set(&new->tgcred->usage, 1);
 256 #endif
 257
 258         atomic_set(&new->usage, 1);
 259 #ifdef CONFIG_DEBUG_CREDENTIALS
 260         new->magic = CRED_MAGIC;
 261 #endif
 262
 263         if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
 264                 goto error;
 265
 266         return new;
 267
 268 error:
 269         abort_creds(new);
 270         return NULL;
 271 }
 272
 273 /**
 274  * prepare_creds - Prepare a new set of credentials for modification
 275  *
 276  * Prepare a new set of task credentials for modification.  A task's creds
 277  * shouldn't generally be modified directly, therefore this function is used to
 278  * prepare a new copy, which the caller then modifies and then commits by
 279  * calling commit_creds().
 280  *
 281  * Preparation involves making a copy of the objective creds for modification.
 282  *
 283  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
 284  *
 285  * Call commit_creds() or abort_creds() to clean up.
 286  */
 287 struct cred *prepare_creds(void)
 288 {
 289         struct task_struct *task = current;
 290         const struct cred *old;
 291         struct cred *new;
 292
 293         validate_process_creds();
 294
 295         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 296         if (!new)
 297                 return NULL;
 298
 299         kdebug("prepare_creds() alloc %p", new);
 300
 301         old = task->cred;
 302         memcpy(new, old, sizeof(struct cred));
 303
 304         atomic_set(&new->usage, 1);
 305         set_cred_subscribers(new, 0);
 306         get_group_info(new->group_info);
 307         get_uid(new->user);
 308
 309 #ifdef CONFIG_KEYS
 310         key_get(new->thread_keyring);
 311         key_get(new->request_key_auth);
 312         atomic_inc(&new->tgcred->usage);
 313 #endif
 314
 315 #ifdef CONFIG_SECURITY
 316         new->security = NULL;
 317 #endif
 318
 319         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 320                 goto error;
 321         validate_creds(new);
 322         return new;
 323
 324 error:
 325         abort_creds(new);
 326         return NULL;
 327 }
 328 EXPORT_SYMBOL(prepare_creds);
 329
 330 /*
 331  * Prepare credentials for current to perform an execve()
 332  * - The caller must hold current->cred_guard_mutex
 333  */
 334 struct cred *prepare_exec_creds(void)
 335 {
 336         struct thread_group_cred *tgcred = NULL;
 337         struct cred *new;
 338
 339 #ifdef CONFIG_KEYS
 340         tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 341         if (!tgcred)
 342                 return NULL;
 343 #endif
 344
 345         new = prepare_creds();
 346         if (!new) {
 347                 kfree(tgcred);
 348                 return new;
 349         }
 350
 351 #ifdef CONFIG_KEYS
 352         /* newly exec'd tasks don't get a thread keyring */
 353         key_put(new->thread_keyring);
 354         new->thread_keyring = NULL;
 355
 356         /* create a new per-thread-group creds for all this set of threads to
 357          * share */
 358         memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
 359
 360         atomic_set(&tgcred->usage, 1);
 361         spin_lock_init(&tgcred->lock);
 362
 363         /* inherit the session keyring; new process keyring */
 364         key_get(tgcred->session_keyring);
 365         tgcred->process_keyring = NULL;
 366
 367         release_tgcred(new);
 368         new->tgcred = tgcred;
 369 #endif
 370
 371         return new;
 372 }
 373
 374 /*
 375  * prepare new credentials for the usermode helper dispatcher
 376  */
 377 struct cred *prepare_usermodehelper_creds(void)
 378 {
 379 #ifdef CONFIG_KEYS
 380         struct thread_group_cred *tgcred = NULL;
 381 #endif
 382         struct cred *new;
 383
 384 #ifdef CONFIG_KEYS
 385         tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
 386         if (!tgcred)
 387                 return NULL;
 388 #endif
 389
 390         new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
 391         if (!new)
 392                 goto free_tgcred;
 393
 394         kdebug("prepare_usermodehelper_creds() alloc %p", new);
 395
 396         memcpy(new, &init_cred, sizeof(struct cred));
 397
 398         atomic_set(&new->usage, 1);
 399         set_cred_subscribers(new, 0);
 400         get_group_info(new->group_info);
 401         get_uid(new->user);
 402
 403 #ifdef CONFIG_KEYS
 404         new->thread_keyring = NULL;
 405         new->request_key_auth = NULL;
 406         new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
 407
 408         atomic_set(&tgcred->usage, 1);
 409         spin_lock_init(&tgcred->lock);
 410         new->tgcred = tgcred;
 411 #endif
 412
 413 #ifdef CONFIG_SECURITY
 414         new->security = NULL;
 415 #endif
 416         if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
 417                 goto error;
 418         validate_creds(new);
 419
 420         BUG_ON(atomic_read(&new->usage) != 1);
 421         return new;
 422
 423 error:
 424         put_cred(new);
 425         return NULL;
 426
 427 free_tgcred:
 428 #ifdef CONFIG_KEYS
 429         kfree(tgcred);
 430 #endif
 431         return NULL;
 432 }
 433
 434 /*
 435  * Copy credentials for the new process created by fork()
 436  *
 437  * We share if we can, but under some circumstances we have to generate a new
 438  * set.
 439  *
 440  * The new process gets the current process's subjective credentials as its
 441  * objective and subjective credentials
 442  */
 443 int copy_creds(struct task_struct *p, unsigned long clone_flags)
 444 {
 445 #ifdef CONFIG_KEYS
 446         struct thread_group_cred *tgcred;
 447 #endif
 448         struct cred *new;
 449         int ret;
 450
 451         mutex_init(&p->cred_guard_mutex);
 452
 453         if (
 454 #ifdef CONFIG_KEYS
 455                 !p->cred->thread_keyring &&
 456 #endif
 457                 clone_flags & CLONE_THREAD
 458             ) {
 459                 p->real_cred = get_cred(p->cred);
 460                 get_cred(p->cred);
 461                 alter_cred_subscribers(p->cred, 2);
 462                 kdebug("share_creds(%p{%d,%d})",
 463                        p->cred, atomic_read(&p->cred->usage),
 464                        read_cred_subscribers(p->cred));
 465                 atomic_inc(&p->cred->user->processes);
 466                 return 0;
 467         }
 468
 469         new = prepare_creds();
 470         if (!new)
 471                 return -ENOMEM;
 472
 473         if (clone_flags & CLONE_NEWUSER) {
 474                 ret = create_user_ns(new);
 475                 if (ret < 0)
 476                         goto error_put;
 477         }
 478
 479 #ifdef CONFIG_KEYS
 480         /* new threads get their own thread keyrings if their parent already
 481          * had one */
 482         if (new->thread_keyring) {
 483                 key_put(new->thread_keyring);
 484                 new->thread_keyring = NULL;
 485                 if (clone_flags & CLONE_THREAD)
 486                         install_thread_keyring_to_cred(new);
 487         }
 488
 489         /* we share the process and session keyrings between all the threads in
 490          * a process - this is slightly icky as we violate COW credentials a
 491          * bit */
 492         if (!(clone_flags & CLONE_THREAD)) {
 493                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 494                 if (!tgcred) {
 495                         ret = -ENOMEM;
 496                         goto error_put;
 497                 }
 498                 atomic_set(&tgcred->usage, 1);
 499                 spin_lock_init(&tgcred->lock);
 500                 tgcred->process_keyring = NULL;
 501                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
 502
 503                 release_tgcred(new);
 504                 new->tgcred = tgcred;
 505         }
 506 #endif
 507
 508         atomic_inc(&new->user->processes);
 509         p->cred = p->real_cred = get_cred(new);
 510         alter_cred_subscribers(new, 2);
 511         validate_creds(new);
 512         return 0;
 513
 514 error_put:
 515         put_cred(new);
 516         return ret;
 517 }
 518
 519 /**
 520  * commit_creds - Install new credentials upon the current task
 521  * @new: The credentials to be assigned
 522  *
 523  * Install a new set of credentials to the current task, using RCU to replace
 524  * the old set.  Both the objective and the subjective credentials pointers are
 525  * updated.  This function may not be called if the subjective credentials are
 526  * in an overridden state.
 527  *
 528  * This function eats the caller's reference to the new credentials.
 529  *
 530  * Always returns 0 thus allowing this function to be tail-called at the end
 531  * of, say, sys_setgid().
 532  */
 533 int commit_creds(struct cred *new)
 534 {
 535         struct task_struct *task = current;
 536         const struct cred *old = task->real_cred;
 537
 538         kdebug("commit_creds(%p{%d,%d})", new,
 539                atomic_read(&new->usage),
 540                read_cred_subscribers(new));
 541
 542         BUG_ON(task->cred != old);
 543 #ifdef CONFIG_DEBUG_CREDENTIALS
 544         BUG_ON(read_cred_subscribers(old) < 2);
 545         validate_creds(old);
 546         validate_creds(new);
 547 #endif
 548         BUG_ON(atomic_read(&new->usage) < 1);
 549
 550         security_commit_creds(new, old);
 551
 552         get_cred(new); /* we will require a ref for the subj creds too */
 553
 554         /* dumpability changes */
 555         if (old->euid != new->euid ||
 556             old->egid != new->egid ||
 557             old->fsuid != new->fsuid ||
 558             old->fsgid != new->fsgid ||
 559             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
 560                 if (task->mm)
 561                         set_dumpable(task->mm, suid_dumpable);
 562                 task->pdeath_signal = 0;
 563                 smp_wmb();
 564         }
 565
 566         /* alter the thread keyring */
 567         if (new->fsuid != old->fsuid)
 568                 key_fsuid_changed(task);
 569         if (new->fsgid != old->fsgid)
 570                 key_fsgid_changed(task);
 571
 572         /* do it
 573          * - What if a process setreuid()'s and this brings the
 574          *   new uid over his NPROC rlimit?  We can check this now
 575          *   cheaply with the new uid cache, so if it matters
 576          *   we should be checking for it.  -DaveM
 577          */
 578         alter_cred_subscribers(new, 2);
 579         if (new->user != old->user)
 580                 atomic_inc(&new->user->processes);
 581         rcu_assign_pointer(task->real_cred, new);
 582         rcu_assign_pointer(task->cred, new);
 583         if (new->user != old->user)
 584                 atomic_dec(&old->user->processes);
 585         alter_cred_subscribers(old, -2);
 586
 587         /* send notifications */
 588         if (new->uid   != old->uid  ||
 589             new->euid  != old->euid ||
 590             new->suid  != old->suid ||
 591             new->fsuid != old->fsuid)
 592                 proc_id_connector(task, PROC_EVENT_UID);
 593
 594         if (new->gid   != old->gid  ||
 595             new->egid  != old->egid ||
 596             new->sgid  != old->sgid ||
 597             new->fsgid != old->fsgid)
 598                 proc_id_connector(task, PROC_EVENT_GID);
 599
 600         /* release the old obj and subj refs both */
 601         put_cred(old);
 602         put_cred(old);
 603         return 0;
 604 }
 605 EXPORT_SYMBOL(commit_creds);
 606
 607 /**
 608  * abort_creds - Discard a set of credentials and unlock the current task
 609  * @new: The credentials that were going to be applied
 610  *
 611  * Discard a set of credentials that were under construction and unlock the
 612  * current task.
 613  */
 614 void abort_creds(struct cred *new)
 615 {
 616         kdebug("abort_creds(%p{%d,%d})", new,
 617                atomic_read(&new->usage),
 618                read_cred_subscribers(new));
 619
 620 #ifdef CONFIG_DEBUG_CREDENTIALS
 621         BUG_ON(read_cred_subscribers(new) != 0);
 622 #endif
 623         BUG_ON(atomic_read(&new->usage) < 1);
 624         put_cred(new);
 625 }
 626 EXPORT_SYMBOL(abort_creds);
 627
 628 /**
 629  * override_creds - Override the current process's subjective credentials
 630  * @new: The credentials to be assigned
 631  *
 632  * Install a set of temporary override subjective credentials on the current
 633  * process, returning the old set for later reversion.
 634  */
 635 const struct cred *override_creds(const struct cred *new)
 636 {
 637         const struct cred *old = current->cred;
 638
 639         kdebug("override_creds(%p{%d,%d})", new,
 640                atomic_read(&new->usage),
 641                read_cred_subscribers(new));
 642
 643         validate_creds(old);
 644         validate_creds(new);
 645         get_cred(new);
 646         alter_cred_subscribers(new, 1);
 647         rcu_assign_pointer(current->cred, new);
 648         alter_cred_subscribers(old, -1);
 649
 650         kdebug("override_creds() = %p{%d,%d}", old,
 651                atomic_read(&old->usage),
 652                read_cred_subscribers(old));
 653         return old;
 654 }
 655 EXPORT_SYMBOL(override_creds);
 656
 657 /**
 658  * revert_creds - Revert a temporary subjective credentials override
 659  * @old: The credentials to be restored
 660  *
 661  * Revert a temporary set of override subjective credentials to an old set,
 662  * discarding the override set.
 663  */
 664 void revert_creds(const struct cred *old)
 665 {
 666         const struct cred *override = current->cred;
 667
 668         kdebug("revert_creds(%p{%d,%d})", old,
 669                atomic_read(&old->usage),
 670                read_cred_subscribers(old));
 671
 672         validate_creds(old);
 673         validate_creds(override);
 674         alter_cred_subscribers(old, 1);
 675         rcu_assign_pointer(current->cred, old);
 676         alter_cred_subscribers(override, -1);
 677         put_cred(override);
 678 }
 679 EXPORT_SYMBOL(revert_creds);
 680
 681 /*
 682  * initialise the credentials stuff
 683  */
 684 void __init cred_init(void)
 685 {
 686         /* allocate a slab in which we can store credentials */
 687         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
 688                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 689 }
 690
 691 /**
 692  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
 693  * @daemon: A userspace daemon to be used as a reference
 694  *
 695  * Prepare a set of credentials for a kernel service.  This can then be used to
 696  * override a task's own credentials so that work can be done on behalf of that
 697  * task that requires a different subjective context.
 698  *
 699  * @daemon is used to provide a base for the security record, but can be NULL.
 700  * If @daemon is supplied, then the security data will be derived from that;
 701  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
 702  *
 703  * The caller may change these controls afterwards if desired.
 704  *
 705  * Returns the new credentials or NULL if out of memory.
 706  *
 707  * Does not take, and does not return holding current->cred_replace_mutex.
 708  */
 709 struct cred *prepare_kernel_cred(struct task_struct *daemon)
 710 {
 711         const struct cred *old;
 712         struct cred *new;
 713
 714         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 715         if (!new)
 716                 return NULL;
 717
 718         kdebug("prepare_kernel_cred() alloc %p", new);
 719
 720         if (daemon)
 721                 old = get_task_cred(daemon);
 722         else
 723                 old = get_cred(&init_cred);
 724
 725         validate_creds(old);
 726
 727         *new = *old;
 728         atomic_set(&new->usage, 1);
 729         set_cred_subscribers(new, 0);
 730         get_uid(new->user);
 731         get_group_info(new->group_info);
 732
 733 #ifdef CONFIG_KEYS
 734         atomic_inc(&init_tgcred.usage);
 735         new->tgcred = &init_tgcred;
 736         new->request_key_auth = NULL;
 737         new->thread_keyring = NULL;
 738         new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 739 #endif
 740
 741 #ifdef CONFIG_SECURITY
 742         new->security = NULL;
 743 #endif
 744         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 745                 goto error;
 746
 747         put_cred(old);
 748         validate_creds(new);
 749         return new;
 750
 751 error:
 752         put_cred(new);
 753         put_cred(old);
 754         return NULL;
 755 }
 756 EXPORT_SYMBOL(prepare_kernel_cred);
 757
 758 /**
 759  * set_security_override - Set the security ID in a set of credentials
 760  * @new: The credentials to alter
 761  * @secid: The LSM security ID to set
 762  *
 763  * Set the LSM security ID in a set of credentials so that the subjective
 764  * security is overridden when an alternative set of credentials is used.
 765  */
 766 int set_security_override(struct cred *new, u32 secid)
 767 {
 768         return security_kernel_act_as(new, secid);
 769 }
 770 EXPORT_SYMBOL(set_security_override);
 771
 772 /**
 773  * set_security_override_from_ctx - Set the security ID in a set of credentials
 774  * @new: The credentials to alter
 775  * @secctx: The LSM security context to generate the security ID from.
 776  *
 777  * Set the LSM security ID in a set of credentials so that the subjective
 778  * security is overridden when an alternative set of credentials is used.  The
 779  * security ID is specified in string form as a security context to be
 780  * interpreted by the LSM.
 781  */
 782 int set_security_override_from_ctx(struct cred *new, const char *secctx)
 783 {
 784         u32 secid;
 785         int ret;
 786
 787         ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
 788         if (ret < 0)
 789                 return ret;
 790
 791         return set_security_override(new, secid);
 792 }
 793 EXPORT_SYMBOL(set_security_override_from_ctx);
 794
 795 /**
 796  * set_create_files_as - Set the LSM file create context in a set of credentials
 797  * @new: The credentials to alter
 798  * @inode: The inode to take the context from
 799  *
 800  * Change the LSM file creation context in a set of credentials to be the same
 801  * as the object context of the specified inode, so that the new inodes have
 802  * the same MAC context as that inode.
 803  */
 804 int set_create_files_as(struct cred *new, struct inode *inode)
 805 {
 806         new->fsuid = inode->i_uid;
 807         new->fsgid = inode->i_gid;
 808         return security_kernel_create_files_as(new, inode);
 809 }
 810 EXPORT_SYMBOL(set_create_files_as);
 811
 812 #ifdef CONFIG_DEBUG_CREDENTIALS
 813
 814 bool creds_are_invalid(const struct cred *cred)
 815 {
 816         if (cred->magic != CRED_MAGIC)
 817                 return true;
 818 #ifdef CONFIG_SECURITY_SELINUX
 819         /*
 820          * cred->security == NULL if security_cred_alloc_blank() or
 821          * security_prepare_creds() returned an error.
 822          */
 823         if (selinux_is_enabled() && cred->security) {
 824                 if ((unsigned long) cred->security < PAGE_SIZE)
 825                         return true;
 826                 if ((*(u32 *)cred->security & 0xffffff00) ==
 827                     (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
 828                         return true;
 829         }
 830 #endif
 831         return false;
 832 }
 833 EXPORT_SYMBOL(creds_are_invalid);
 834
 835 /*
 836  * dump invalid credentials
 837  */
 838 static void dump_invalid_creds(const struct cred *cred, const char *label,
 839                                const struct task_struct *tsk)
 840 {
 841         printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
 842                label, cred,
 843                cred == &init_cred ? "[init]" : "",
 844                cred == tsk->real_cred ? "[real]" : "",
 845                cred == tsk->cred ? "[eff]" : "");
 846         printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
 847                cred->magic, cred->put_addr);
 848         printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
 849                atomic_read(&cred->usage),
 850                read_cred_subscribers(cred));
 851         printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
 852                cred->uid, cred->euid, cred->suid, cred->fsuid);
 853         printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
 854                cred->gid, cred->egid, cred->sgid, cred->fsgid);
 855 #ifdef CONFIG_SECURITY
 856         printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
 857         if ((unsigned long) cred->security >= PAGE_SIZE &&
 858             (((unsigned long) cred->security & 0xffffff00) !=
 859              (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
 860                 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
 861                        ((u32*)cred->security)[0],
 862                        ((u32*)cred->security)[1]);
 863 #endif
 864 }
 865
 866 /*
 867  * report use of invalid credentials
 868  */
 869 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
 870 {
 871         printk(KERN_ERR "CRED: Invalid credentials\n");
 872         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 873         dump_invalid_creds(cred, "Specified", current);
 874         BUG();
 875 }
 876 EXPORT_SYMBOL(__invalid_creds);
 877
 878 /*
 879  * check the credentials on a process
 880  */
 881 void __validate_process_creds(struct task_struct *tsk,
 882                               const char *file, unsigned line)
 883 {
 884         if (tsk->cred == tsk->real_cred) {
 885                 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
 886                              creds_are_invalid(tsk->cred)))
 887                         goto invalid_creds;
 888         } else {
 889                 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
 890                              read_cred_subscribers(tsk->cred) < 1 ||
 891                              creds_are_invalid(tsk->real_cred) ||
 892                              creds_are_invalid(tsk->cred)))
 893                         goto invalid_creds;
 894         }
 895         return;
 896
 897 invalid_creds:
 898         printk(KERN_ERR "CRED: Invalid process credentials\n");
 899         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 900
 901         dump_invalid_creds(tsk->real_cred, "Real", tsk);
 902         if (tsk->cred != tsk->real_cred)
 903                 dump_invalid_creds(tsk->cred, "Effective", tsk);
 904         else
 905                 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
 906         BUG();
 907 }
 908 EXPORT_SYMBOL(__validate_process_creds);
 909
 910 /*
 911  * check creds for do_exit()
 912  */
 913 void validate_creds_for_do_exit(struct task_struct *tsk)
 914 {
 915         kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
 916                tsk->real_cred, tsk->cred,
 917                atomic_read(&tsk->cred->usage),
 918                read_cred_subscribers(tsk->cred));
 919
 920         __validate_process_creds(tsk, __FILE__, __LINE__);
 921 }
 922
 923 #endif /* CONFIG_DEBUG_CREDENTIALS */