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/sched.h>
  14 #include <linux/key.h>
  15 #include <linux/keyctl.h>
  16 #include <linux/init_task.h>
  17 #include <linux/security.h>
  18 #include <linux/cn_proc.h>
  19
  20 #if 0
  21 #define kdebug(FMT, ...) \
  22         printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
  23 #else
  24 static inline __attribute__((format(printf, 1, 2)))
  25 void no_printk(const char *fmt, ...)
  26 {
  27 }
  28 #define kdebug(FMT, ...) \
  29         no_printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
  30 #endif
  31
  32 static struct kmem_cache *cred_jar;
  33
  34 /*
  35  * The common credentials for the initial task's thread group
  36  */
  37 #ifdef CONFIG_KEYS
  38 static struct thread_group_cred init_tgcred = {
  39         .usage  = ATOMIC_INIT(2),
  40         .tgid   = 0,
  41         .lock   = SPIN_LOCK_UNLOCKED,
  42 };
  43 #endif
  44
  45 /*
  46  * The initial credentials for the initial task
  47  */
  48 struct cred init_cred = {
  49         .usage                  = ATOMIC_INIT(4),
  50 #ifdef CONFIG_DEBUG_CREDENTIALS
  51         .subscribers            = ATOMIC_INIT(2),
  52         .magic                  = CRED_MAGIC,
  53 #endif
  54         .securebits             = SECUREBITS_DEFAULT,
  55         .cap_inheritable        = CAP_INIT_INH_SET,
  56         .cap_permitted          = CAP_FULL_SET,
  57         .cap_effective          = CAP_INIT_EFF_SET,
  58         .cap_bset               = CAP_INIT_BSET,
  59         .user                   = INIT_USER,
  60         .group_info             = &init_groups,
  61 #ifdef CONFIG_KEYS
  62         .tgcred                 = &init_tgcred,
  63 #endif
  64 };
  65
  66 static inline void set_cred_subscribers(struct cred *cred, int n)
  67 {
  68 #ifdef CONFIG_DEBUG_CREDENTIALS
  69         atomic_set(&cred->subscribers, n);
  70 #endif
  71 }
  72
  73 static inline int read_cred_subscribers(const struct cred *cred)
  74 {
  75 #ifdef CONFIG_DEBUG_CREDENTIALS
  76         return atomic_read(&cred->subscribers);
  77 #else
  78         return 0;
  79 #endif
  80 }
  81
  82 static inline void alter_cred_subscribers(const struct cred *_cred, int n)
  83 {
  84 #ifdef CONFIG_DEBUG_CREDENTIALS
  85         struct cred *cred = (struct cred *) _cred;
  86
  87         atomic_add(n, &cred->subscribers);
  88 #endif
  89 }
  90
  91 /*
  92  * Dispose of the shared task group credentials
  93  */
  94 #ifdef CONFIG_KEYS
  95 static void release_tgcred_rcu(struct rcu_head *rcu)
  96 {
  97         struct thread_group_cred *tgcred =
  98                 container_of(rcu, struct thread_group_cred, rcu);
  99
 100         BUG_ON(atomic_read(&tgcred->usage) != 0);
 101
 102         key_put(tgcred->session_keyring);
 103         key_put(tgcred->process_keyring);
 104         kfree(tgcred);
 105 }
 106 #endif
 107
 108 /*
 109  * Release a set of thread group credentials.
 110  */
 111 static void release_tgcred(struct cred *cred)
 112 {
 113 #ifdef CONFIG_KEYS
 114         struct thread_group_cred *tgcred = cred->tgcred;
 115
 116         if (atomic_dec_and_test(&tgcred->usage))
 117                 call_rcu(&tgcred->rcu, release_tgcred_rcu);
 118 #endif
 119 }
 120
 121 /*
 122  * The RCU callback to actually dispose of a set of credentials
 123  */
 124 static void put_cred_rcu(struct rcu_head *rcu)
 125 {
 126         struct cred *cred = container_of(rcu, struct cred, rcu);
 127
 128         kdebug("put_cred_rcu(%p)", cred);
 129
 130 #ifdef CONFIG_DEBUG_CREDENTIALS
 131         if (cred->magic != CRED_MAGIC_DEAD ||
 132             atomic_read(&cred->usage) != 0 ||
 133             read_cred_subscribers(cred) != 0)
 134                 panic("CRED: put_cred_rcu() sees %p with"
 135                       " mag %x, put %p, usage %d, subscr %d\n",
 136                       cred, cred->magic, cred->put_addr,
 137                       atomic_read(&cred->usage),
 138                       read_cred_subscribers(cred));
 139 #else
 140         if (atomic_read(&cred->usage) != 0)
 141                 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
 142                       cred, atomic_read(&cred->usage));
 143 #endif
 144
 145         security_cred_free(cred);
 146         key_put(cred->thread_keyring);
 147         key_put(cred->request_key_auth);
 148         release_tgcred(cred);
 149         if (cred->group_info)
 150                 put_group_info(cred->group_info);
 151         free_uid(cred->user);
 152         kmem_cache_free(cred_jar, cred);
 153 }
 154
 155 /**
 156  * __put_cred - Destroy a set of credentials
 157  * @cred: The record to release
 158  *
 159  * Destroy a set of credentials on which no references remain.
 160  */
 161 void __put_cred(struct cred *cred)
 162 {
 163         kdebug("__put_cred(%p{%d,%d})", cred,
 164                atomic_read(&cred->usage),
 165                read_cred_subscribers(cred));
 166
 167         BUG_ON(atomic_read(&cred->usage) != 0);
 168 #ifdef CONFIG_DEBUG_CREDENTIALS
 169         BUG_ON(read_cred_subscribers(cred) != 0);
 170         cred->magic = CRED_MAGIC_DEAD;
 171         cred->put_addr = __builtin_return_address(0);
 172 #endif
 173         BUG_ON(cred == current->cred);
 174         BUG_ON(cred == current->real_cred);
 175
 176         call_rcu(&cred->rcu, put_cred_rcu);
 177 }
 178 EXPORT_SYMBOL(__put_cred);
 179
 180 /*
 181  * Clean up a task's credentials when it exits
 182  */
 183 void exit_creds(struct task_struct *tsk)
 184 {
 185         struct cred *cred;
 186
 187         kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
 188                atomic_read(&tsk->cred->usage),
 189                read_cred_subscribers(tsk->cred));
 190
 191         cred = (struct cred *) tsk->real_cred;
 192         tsk->real_cred = NULL;
 193         validate_creds(cred);
 194         alter_cred_subscribers(cred, -1);
 195         put_cred(cred);
 196
 197         cred = (struct cred *) tsk->cred;
 198         tsk->cred = NULL;
 199         validate_creds(cred);
 200         alter_cred_subscribers(cred, -1);
 201         put_cred(cred);
 202
 203         cred = (struct cred *) tsk->replacement_session_keyring;
 204         if (cred) {
 205                 tsk->replacement_session_keyring = NULL;
 206                 validate_creds(cred);
 207                 put_cred(cred);
 208         }
 209 }
 210
 211 /*
 212  * Allocate blank credentials, such that the credentials can be filled in at a
 213  * later date without risk of ENOMEM.
 214  */
 215 struct cred *cred_alloc_blank(void)
 216 {
 217         struct cred *new;
 218
 219         new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
 220         if (!new)
 221                 return NULL;
 222
 223 #ifdef CONFIG_KEYS
 224         new->tgcred = kzalloc(sizeof(*new->tgcred), GFP_KERNEL);
 225         if (!new->tgcred) {
 226                 kmem_cache_free(cred_jar, new);
 227                 return NULL;
 228         }
 229         atomic_set(&new->tgcred->usage, 1);
 230 #endif
 231
 232         atomic_set(&new->usage, 1);
 233
 234         if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
 235                 goto error;
 236
 237 #ifdef CONFIG_DEBUG_CREDENTIALS
 238         new->magic = CRED_MAGIC;
 239 #endif
 240         return new;
 241
 242 error:
 243         abort_creds(new);
 244         return NULL;
 245 }
 246
 247 /**
 248  * prepare_creds - Prepare a new set of credentials for modification
 249  *
 250  * Prepare a new set of task credentials for modification.  A task's creds
 251  * shouldn't generally be modified directly, therefore this function is used to
 252  * prepare a new copy, which the caller then modifies and then commits by
 253  * calling commit_creds().
 254  *
 255  * Preparation involves making a copy of the objective creds for modification.
 256  *
 257  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
 258  *
 259  * Call commit_creds() or abort_creds() to clean up.
 260  */
 261 struct cred *prepare_creds(void)
 262 {
 263         struct task_struct *task = current;
 264         const struct cred *old;
 265         struct cred *new;
 266
 267         validate_process_creds();
 268
 269         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 270         if (!new)
 271                 return NULL;
 272
 273         kdebug("prepare_creds() alloc %p", new);
 274
 275         old = task->cred;
 276         memcpy(new, old, sizeof(struct cred));
 277
 278         atomic_set(&new->usage, 1);
 279         set_cred_subscribers(new, 0);
 280         get_group_info(new->group_info);
 281         get_uid(new->user);
 282
 283 #ifdef CONFIG_KEYS
 284         key_get(new->thread_keyring);
 285         key_get(new->request_key_auth);
 286         atomic_inc(&new->tgcred->usage);
 287 #endif
 288
 289 #ifdef CONFIG_SECURITY
 290         new->security = NULL;
 291 #endif
 292
 293         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 294                 goto error;
 295         validate_creds(new);
 296         return new;
 297
 298 error:
 299         abort_creds(new);
 300         return NULL;
 301 }
 302 EXPORT_SYMBOL(prepare_creds);
 303
 304 /*
 305  * Prepare credentials for current to perform an execve()
 306  * - The caller must hold current->cred_guard_mutex
 307  */
 308 struct cred *prepare_exec_creds(void)
 309 {
 310         struct thread_group_cred *tgcred = NULL;
 311         struct cred *new;
 312
 313 #ifdef CONFIG_KEYS
 314         tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 315         if (!tgcred)
 316                 return NULL;
 317 #endif
 318
 319         new = prepare_creds();
 320         if (!new) {
 321                 kfree(tgcred);
 322                 return new;
 323         }
 324
 325 #ifdef CONFIG_KEYS
 326         /* newly exec'd tasks don't get a thread keyring */
 327         key_put(new->thread_keyring);
 328         new->thread_keyring = NULL;
 329
 330         /* create a new per-thread-group creds for all this set of threads to
 331          * share */
 332         memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
 333
 334         atomic_set(&tgcred->usage, 1);
 335         spin_lock_init(&tgcred->lock);
 336
 337         /* inherit the session keyring; new process keyring */
 338         key_get(tgcred->session_keyring);
 339         tgcred->process_keyring = NULL;
 340
 341         release_tgcred(new);
 342         new->tgcred = tgcred;
 343 #endif
 344
 345         return new;
 346 }
 347
 348 /*
 349  * prepare new credentials for the usermode helper dispatcher
 350  */
 351 struct cred *prepare_usermodehelper_creds(void)
 352 {
 353 #ifdef CONFIG_KEYS
 354         struct thread_group_cred *tgcred = NULL;
 355 #endif
 356         struct cred *new;
 357
 358 #ifdef CONFIG_KEYS
 359         tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
 360         if (!tgcred)
 361                 return NULL;
 362 #endif
 363
 364         new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
 365         if (!new)
 366                 return NULL;
 367
 368         kdebug("prepare_usermodehelper_creds() alloc %p", new);
 369
 370         memcpy(new, &init_cred, sizeof(struct cred));
 371
 372         atomic_set(&new->usage, 1);
 373         set_cred_subscribers(new, 0);
 374         get_group_info(new->group_info);
 375         get_uid(new->user);
 376
 377 #ifdef CONFIG_KEYS
 378         new->thread_keyring = NULL;
 379         new->request_key_auth = NULL;
 380         new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
 381
 382         atomic_set(&tgcred->usage, 1);
 383         spin_lock_init(&tgcred->lock);
 384         new->tgcred = tgcred;
 385 #endif
 386
 387 #ifdef CONFIG_SECURITY
 388         new->security = NULL;
 389 #endif
 390         if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
 391                 goto error;
 392         validate_creds(new);
 393
 394         BUG_ON(atomic_read(&new->usage) != 1);
 395         return new;
 396
 397 error:
 398         put_cred(new);
 399         return NULL;
 400 }
 401
 402 /*
 403  * Copy credentials for the new process created by fork()
 404  *
 405  * We share if we can, but under some circumstances we have to generate a new
 406  * set.
 407  *
 408  * The new process gets the current process's subjective credentials as its
 409  * objective and subjective credentials
 410  */
 411 int copy_creds(struct task_struct *p, unsigned long clone_flags)
 412 {
 413 #ifdef CONFIG_KEYS
 414         struct thread_group_cred *tgcred;
 415 #endif
 416         struct cred *new;
 417         int ret;
 418
 419         mutex_init(&p->cred_guard_mutex);
 420
 421         if (
 422 #ifdef CONFIG_KEYS
 423                 !p->cred->thread_keyring &&
 424 #endif
 425                 clone_flags & CLONE_THREAD
 426             ) {
 427                 p->real_cred = get_cred(p->cred);
 428                 get_cred(p->cred);
 429                 alter_cred_subscribers(p->cred, 2);
 430                 kdebug("share_creds(%p{%d,%d})",
 431                        p->cred, atomic_read(&p->cred->usage),
 432                        read_cred_subscribers(p->cred));
 433                 atomic_inc(&p->cred->user->processes);
 434                 return 0;
 435         }
 436
 437         new = prepare_creds();
 438         if (!new)
 439                 return -ENOMEM;
 440
 441         if (clone_flags & CLONE_NEWUSER) {
 442                 ret = create_user_ns(new);
 443                 if (ret < 0)
 444                         goto error_put;
 445         }
 446
 447 #ifdef CONFIG_KEYS
 448         /* new threads get their own thread keyrings if their parent already
 449          * had one */
 450         if (new->thread_keyring) {
 451                 key_put(new->thread_keyring);
 452                 new->thread_keyring = NULL;
 453                 if (clone_flags & CLONE_THREAD)
 454                         install_thread_keyring_to_cred(new);
 455         }
 456
 457         /* we share the process and session keyrings between all the threads in
 458          * a process - this is slightly icky as we violate COW credentials a
 459          * bit */
 460         if (!(clone_flags & CLONE_THREAD)) {
 461                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 462                 if (!tgcred) {
 463                         ret = -ENOMEM;
 464                         goto error_put;
 465                 }
 466                 atomic_set(&tgcred->usage, 1);
 467                 spin_lock_init(&tgcred->lock);
 468                 tgcred->process_keyring = NULL;
 469                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
 470
 471                 release_tgcred(new);
 472                 new->tgcred = tgcred;
 473         }
 474 #endif
 475
 476         atomic_inc(&new->user->processes);
 477         p->cred = p->real_cred = get_cred(new);
 478         alter_cred_subscribers(new, 2);
 479         validate_creds(new);
 480         return 0;
 481
 482 error_put:
 483         put_cred(new);
 484         return ret;
 485 }
 486
 487 /**
 488  * commit_creds - Install new credentials upon the current task
 489  * @new: The credentials to be assigned
 490  *
 491  * Install a new set of credentials to the current task, using RCU to replace
 492  * the old set.  Both the objective and the subjective credentials pointers are
 493  * updated.  This function may not be called if the subjective credentials are
 494  * in an overridden state.
 495  *
 496  * This function eats the caller's reference to the new credentials.
 497  *
 498  * Always returns 0 thus allowing this function to be tail-called at the end
 499  * of, say, sys_setgid().
 500  */
 501 int commit_creds(struct cred *new)
 502 {
 503         struct task_struct *task = current;
 504         const struct cred *old = task->real_cred;
 505
 506         kdebug("commit_creds(%p{%d,%d})", new,
 507                atomic_read(&new->usage),
 508                read_cred_subscribers(new));
 509
 510         BUG_ON(task->cred != old);
 511 #ifdef CONFIG_DEBUG_CREDENTIALS
 512         BUG_ON(read_cred_subscribers(old) < 2);
 513         validate_creds(old);
 514         validate_creds(new);
 515 #endif
 516         BUG_ON(atomic_read(&new->usage) < 1);
 517
 518         security_commit_creds(new, old);
 519
 520         get_cred(new); /* we will require a ref for the subj creds too */
 521
 522         /* dumpability changes */
 523         if (old->euid != new->euid ||
 524             old->egid != new->egid ||
 525             old->fsuid != new->fsuid ||
 526             old->fsgid != new->fsgid ||
 527             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
 528                 if (task->mm)
 529                         set_dumpable(task->mm, suid_dumpable);
 530                 task->pdeath_signal = 0;
 531                 smp_wmb();
 532         }
 533
 534         /* alter the thread keyring */
 535         if (new->fsuid != old->fsuid)
 536                 key_fsuid_changed(task);
 537         if (new->fsgid != old->fsgid)
 538                 key_fsgid_changed(task);
 539
 540         /* do it
 541          * - What if a process setreuid()'s and this brings the
 542          *   new uid over his NPROC rlimit?  We can check this now
 543          *   cheaply with the new uid cache, so if it matters
 544          *   we should be checking for it.  -DaveM
 545          */
 546         alter_cred_subscribers(new, 2);
 547         if (new->user != old->user)
 548                 atomic_inc(&new->user->processes);
 549         rcu_assign_pointer(task->real_cred, new);
 550         rcu_assign_pointer(task->cred, new);
 551         if (new->user != old->user)
 552                 atomic_dec(&old->user->processes);
 553         alter_cred_subscribers(old, -2);
 554
 555         /* send notifications */
 556         if (new->uid   != old->uid  ||
 557             new->euid  != old->euid ||
 558             new->suid  != old->suid ||
 559             new->fsuid != old->fsuid)
 560                 proc_id_connector(task, PROC_EVENT_UID);
 561
 562         if (new->gid   != old->gid  ||
 563             new->egid  != old->egid ||
 564             new->sgid  != old->sgid ||
 565             new->fsgid != old->fsgid)
 566                 proc_id_connector(task, PROC_EVENT_GID);
 567
 568         /* release the old obj and subj refs both */
 569         put_cred(old);
 570         put_cred(old);
 571         return 0;
 572 }
 573 EXPORT_SYMBOL(commit_creds);
 574
 575 /**
 576  * abort_creds - Discard a set of credentials and unlock the current task
 577  * @new: The credentials that were going to be applied
 578  *
 579  * Discard a set of credentials that were under construction and unlock the
 580  * current task.
 581  */
 582 void abort_creds(struct cred *new)
 583 {
 584         kdebug("abort_creds(%p{%d,%d})", new,
 585                atomic_read(&new->usage),
 586                read_cred_subscribers(new));
 587
 588 #ifdef CONFIG_DEBUG_CREDENTIALS
 589         BUG_ON(read_cred_subscribers(new) != 0);
 590 #endif
 591         BUG_ON(atomic_read(&new->usage) < 1);
 592         put_cred(new);
 593 }
 594 EXPORT_SYMBOL(abort_creds);
 595
 596 /**
 597  * override_creds - Override the current process's subjective credentials
 598  * @new: The credentials to be assigned
 599  *
 600  * Install a set of temporary override subjective credentials on the current
 601  * process, returning the old set for later reversion.
 602  */
 603 const struct cred *override_creds(const struct cred *new)
 604 {
 605         const struct cred *old = current->cred;
 606
 607         kdebug("override_creds(%p{%d,%d})", new,
 608                atomic_read(&new->usage),
 609                read_cred_subscribers(new));
 610
 611         validate_creds(old);
 612         validate_creds(new);
 613         get_cred(new);
 614         alter_cred_subscribers(new, 1);
 615         rcu_assign_pointer(current->cred, new);
 616         alter_cred_subscribers(old, -1);
 617
 618         kdebug("override_creds() = %p{%d,%d}", old,
 619                atomic_read(&old->usage),
 620                read_cred_subscribers(old));
 621         return old;
 622 }
 623 EXPORT_SYMBOL(override_creds);
 624
 625 /**
 626  * revert_creds - Revert a temporary subjective credentials override
 627  * @old: The credentials to be restored
 628  *
 629  * Revert a temporary set of override subjective credentials to an old set,
 630  * discarding the override set.
 631  */
 632 void revert_creds(const struct cred *old)
 633 {
 634         const struct cred *override = current->cred;
 635
 636         kdebug("revert_creds(%p{%d,%d})", old,
 637                atomic_read(&old->usage),
 638                read_cred_subscribers(old));
 639
 640         validate_creds(old);
 641         validate_creds(override);
 642         alter_cred_subscribers(old, 1);
 643         rcu_assign_pointer(current->cred, old);
 644         alter_cred_subscribers(override, -1);
 645         put_cred(override);
 646 }
 647 EXPORT_SYMBOL(revert_creds);
 648
 649 /*
 650  * initialise the credentials stuff
 651  */
 652 void __init cred_init(void)
 653 {
 654         /* allocate a slab in which we can store credentials */
 655         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
 656                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 657 }
 658
 659 /**
 660  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
 661  * @daemon: A userspace daemon to be used as a reference
 662  *
 663  * Prepare a set of credentials for a kernel service.  This can then be used to
 664  * override a task's own credentials so that work can be done on behalf of that
 665  * task that requires a different subjective context.
 666  *
 667  * @daemon is used to provide a base for the security record, but can be NULL.
 668  * If @daemon is supplied, then the security data will be derived from that;
 669  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
 670  *
 671  * The caller may change these controls afterwards if desired.
 672  *
 673  * Returns the new credentials or NULL if out of memory.
 674  *
 675  * Does not take, and does not return holding current->cred_replace_mutex.
 676  */
 677 struct cred *prepare_kernel_cred(struct task_struct *daemon)
 678 {
 679         const struct cred *old;
 680         struct cred *new;
 681
 682         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 683         if (!new)
 684                 return NULL;
 685
 686         kdebug("prepare_kernel_cred() alloc %p", new);
 687
 688         if (daemon)
 689                 old = get_task_cred(daemon);
 690         else
 691                 old = get_cred(&init_cred);
 692
 693         validate_creds(old);
 694
 695         *new = *old;
 696         get_uid(new->user);
 697         get_group_info(new->group_info);
 698
 699 #ifdef CONFIG_KEYS
 700         atomic_inc(&init_tgcred.usage);
 701         new->tgcred = &init_tgcred;
 702         new->request_key_auth = NULL;
 703         new->thread_keyring = NULL;
 704         new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 705 #endif
 706
 707 #ifdef CONFIG_SECURITY
 708         new->security = NULL;
 709 #endif
 710         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 711                 goto error;
 712
 713         atomic_set(&new->usage, 1);
 714         set_cred_subscribers(new, 0);
 715         put_cred(old);
 716         validate_creds(new);
 717         return new;
 718
 719 error:
 720         put_cred(new);
 721         put_cred(old);
 722         return NULL;
 723 }
 724 EXPORT_SYMBOL(prepare_kernel_cred);
 725
 726 /**
 727  * set_security_override - Set the security ID in a set of credentials
 728  * @new: The credentials to alter
 729  * @secid: The LSM security ID to set
 730  *
 731  * Set the LSM security ID in a set of credentials so that the subjective
 732  * security is overridden when an alternative set of credentials is used.
 733  */
 734 int set_security_override(struct cred *new, u32 secid)
 735 {
 736         return security_kernel_act_as(new, secid);
 737 }
 738 EXPORT_SYMBOL(set_security_override);
 739
 740 /**
 741  * set_security_override_from_ctx - Set the security ID in a set of credentials
 742  * @new: The credentials to alter
 743  * @secctx: The LSM security context to generate the security ID from.
 744  *
 745  * Set the LSM security ID in a set of credentials so that the subjective
 746  * security is overridden when an alternative set of credentials is used.  The
 747  * security ID is specified in string form as a security context to be
 748  * interpreted by the LSM.
 749  */
 750 int set_security_override_from_ctx(struct cred *new, const char *secctx)
 751 {
 752         u32 secid;
 753         int ret;
 754
 755         ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
 756         if (ret < 0)
 757                 return ret;
 758
 759         return set_security_override(new, secid);
 760 }
 761 EXPORT_SYMBOL(set_security_override_from_ctx);
 762
 763 /**
 764  * set_create_files_as - Set the LSM file create context in a set of credentials
 765  * @new: The credentials to alter
 766  * @inode: The inode to take the context from
 767  *
 768  * Change the LSM file creation context in a set of credentials to be the same
 769  * as the object context of the specified inode, so that the new inodes have
 770  * the same MAC context as that inode.
 771  */
 772 int set_create_files_as(struct cred *new, struct inode *inode)
 773 {
 774         new->fsuid = inode->i_uid;
 775         new->fsgid = inode->i_gid;
 776         return security_kernel_create_files_as(new, inode);
 777 }
 778 EXPORT_SYMBOL(set_create_files_as);
 779
 780 #ifdef CONFIG_DEBUG_CREDENTIALS
 781
 782 bool creds_are_invalid(const struct cred *cred)
 783 {
 784         if (cred->magic != CRED_MAGIC)
 785                 return true;
 786 #ifdef CONFIG_SECURITY_SELINUX
 787         if (selinux_is_enabled()) {
 788                 if ((unsigned long) cred->security < PAGE_SIZE)
 789                         return true;
 790                 if ((*(u32 *)cred->security & 0xffffff00) ==
 791                     (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
 792                         return true;
 793         }
 794 #endif
 795         return false;
 796 }
 797 EXPORT_SYMBOL(creds_are_invalid);
 798
 799 /*
 800  * dump invalid credentials
 801  */
 802 static void dump_invalid_creds(const struct cred *cred, const char *label,
 803                                const struct task_struct *tsk)
 804 {
 805         printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
 806                label, cred,
 807                cred == &init_cred ? "[init]" : "",
 808                cred == tsk->real_cred ? "[real]" : "",
 809                cred == tsk->cred ? "[eff]" : "");
 810         printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
 811                cred->magic, cred->put_addr);
 812         printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
 813                atomic_read(&cred->usage),
 814                read_cred_subscribers(cred));
 815         printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
 816                cred->uid, cred->euid, cred->suid, cred->fsuid);
 817         printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
 818                cred->gid, cred->egid, cred->sgid, cred->fsgid);
 819 #ifdef CONFIG_SECURITY
 820         printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
 821         if ((unsigned long) cred->security >= PAGE_SIZE &&
 822             (((unsigned long) cred->security & 0xffffff00) !=
 823              (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
 824                 printk(KERN_ERR "CRED: ->security {%x, %x}\n",
 825                        ((u32*)cred->security)[0],
 826                        ((u32*)cred->security)[1]);
 827 #endif
 828 }
 829
 830 /*
 831  * report use of invalid credentials
 832  */
 833 void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
 834 {
 835         printk(KERN_ERR "CRED: Invalid credentials\n");
 836         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 837         dump_invalid_creds(cred, "Specified", current);
 838         BUG();
 839 }
 840 EXPORT_SYMBOL(__invalid_creds);
 841
 842 /*
 843  * check the credentials on a process
 844  */
 845 void __validate_process_creds(struct task_struct *tsk,
 846                               const char *file, unsigned line)
 847 {
 848         if (tsk->cred == tsk->real_cred) {
 849                 if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
 850                              creds_are_invalid(tsk->cred)))
 851                         goto invalid_creds;
 852         } else {
 853                 if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
 854                              read_cred_subscribers(tsk->cred) < 1 ||
 855                              creds_are_invalid(tsk->real_cred) ||
 856                              creds_are_invalid(tsk->cred)))
 857                         goto invalid_creds;
 858         }
 859         return;
 860
 861 invalid_creds:
 862         printk(KERN_ERR "CRED: Invalid process credentials\n");
 863         printk(KERN_ERR "CRED: At %s:%u\n", file, line);
 864
 865         dump_invalid_creds(tsk->real_cred, "Real", tsk);
 866         if (tsk->cred != tsk->real_cred)
 867                 dump_invalid_creds(tsk->cred, "Effective", tsk);
 868         else
 869                 printk(KERN_ERR "CRED: Effective creds == Real creds\n");
 870         BUG();
 871 }
 872 EXPORT_SYMBOL(__validate_process_creds);
 873
 874 /*
 875  * check creds for do_exit()
 876  */
 877 void validate_creds_for_do_exit(struct task_struct *tsk)
 878 {
 879         kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
 880                tsk->real_cred, tsk->cred,
 881                atomic_read(&tsk->cred->usage),
 882                read_cred_subscribers(tsk->cred));
 883
 884         __validate_process_creds(tsk, __FILE__, __LINE__);
 885 }
 886
 887 #endif /* CONFIG_DEBUG_CREDENTIALS */