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 #include "cred-internals.h"
  20
  21 static struct kmem_cache *cred_jar;
  22
  23 /*
  24  * The common credentials for the initial task's thread group
  25  */
  26 #ifdef CONFIG_KEYS
  27 static struct thread_group_cred init_tgcred = {
  28         .usage  = ATOMIC_INIT(2),
  29         .tgid   = 0,
  30         .lock   = SPIN_LOCK_UNLOCKED,
  31 };
  32 #endif
  33
  34 /*
  35  * The initial credentials for the initial task
  36  */
  37 struct cred init_cred = {
  38         .usage                  = ATOMIC_INIT(4),
  39         .securebits             = SECUREBITS_DEFAULT,
  40         .cap_inheritable        = CAP_INIT_INH_SET,
  41         .cap_permitted          = CAP_FULL_SET,
  42         .cap_effective          = CAP_INIT_EFF_SET,
  43         .cap_bset               = CAP_INIT_BSET,
  44         .user                   = INIT_USER,
  45         .group_info             = &init_groups,
  46 #ifdef CONFIG_KEYS
  47         .tgcred                 = &init_tgcred,
  48 #endif
  49 };
  50
  51 /*
  52  * Dispose of the shared task group credentials
  53  */
  54 #ifdef CONFIG_KEYS
  55 static void release_tgcred_rcu(struct rcu_head *rcu)
  56 {
  57         struct thread_group_cred *tgcred =
  58                 container_of(rcu, struct thread_group_cred, rcu);
  59
  60         BUG_ON(atomic_read(&tgcred->usage) != 0);
  61
  62         key_put(tgcred->session_keyring);
  63         key_put(tgcred->process_keyring);
  64         kfree(tgcred);
  65 }
  66 #endif
  67
  68 /*
  69  * Release a set of thread group credentials.
  70  */
  71 static void release_tgcred(struct cred *cred)
  72 {
  73 #ifdef CONFIG_KEYS
  74         struct thread_group_cred *tgcred = cred->tgcred;
  75
  76         if (atomic_dec_and_test(&tgcred->usage))
  77                 call_rcu(&tgcred->rcu, release_tgcred_rcu);
  78 #endif
  79 }
  80
  81 /*
  82  * The RCU callback to actually dispose of a set of credentials
  83  */
  84 static void put_cred_rcu(struct rcu_head *rcu)
  85 {
  86         struct cred *cred = container_of(rcu, struct cred, rcu);
  87
  88         if (atomic_read(&cred->usage) != 0)
  89                 panic("CRED: put_cred_rcu() sees %p with usage %d\n",
  90                       cred, atomic_read(&cred->usage));
  91
  92         security_cred_free(cred);
  93         key_put(cred->thread_keyring);
  94         key_put(cred->request_key_auth);
  95         release_tgcred(cred);
  96         put_group_info(cred->group_info);
  97         free_uid(cred->user);
  98         kmem_cache_free(cred_jar, cred);
  99 }
 100
 101 /**
 102  * __put_cred - Destroy a set of credentials
 103  * @cred: The record to release
 104  *
 105  * Destroy a set of credentials on which no references remain.
 106  */
 107 void __put_cred(struct cred *cred)
 108 {
 109         BUG_ON(atomic_read(&cred->usage) != 0);
 110
 111         call_rcu(&cred->rcu, put_cred_rcu);
 112 }
 113 EXPORT_SYMBOL(__put_cred);
 114
 115 /**
 116  * prepare_creds - Prepare a new set of credentials for modification
 117  *
 118  * Prepare a new set of task credentials for modification.  A task's creds
 119  * shouldn't generally be modified directly, therefore this function is used to
 120  * prepare a new copy, which the caller then modifies and then commits by
 121  * calling commit_creds().
 122  *
 123  * Preparation involves making a copy of the objective creds for modification.
 124  *
 125  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
 126  *
 127  * Call commit_creds() or abort_creds() to clean up.
 128  */
 129 struct cred *prepare_creds(void)
 130 {
 131         struct task_struct *task = current;
 132         const struct cred *old;
 133         struct cred *new;
 134
 135         BUG_ON(atomic_read(&task->real_cred->usage) < 1);
 136
 137         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 138         if (!new)
 139                 return NULL;
 140
 141         old = task->cred;
 142         memcpy(new, old, sizeof(struct cred));
 143
 144         atomic_set(&new->usage, 1);
 145         get_group_info(new->group_info);
 146         get_uid(new->user);
 147
 148 #ifdef CONFIG_KEYS
 149         key_get(new->thread_keyring);
 150         key_get(new->request_key_auth);
 151         atomic_inc(&new->tgcred->usage);
 152 #endif
 153
 154 #ifdef CONFIG_SECURITY
 155         new->security = NULL;
 156 #endif
 157
 158         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 159                 goto error;
 160         return new;
 161
 162 error:
 163         abort_creds(new);
 164         return NULL;
 165 }
 166 EXPORT_SYMBOL(prepare_creds);
 167
 168 /*
 169  * Prepare credentials for current to perform an execve()
 170  * - The caller must hold current->cred_exec_mutex
 171  */
 172 struct cred *prepare_exec_creds(void)
 173 {
 174         struct thread_group_cred *tgcred = NULL;
 175         struct cred *new;
 176
 177 #ifdef CONFIG_KEYS
 178         tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 179         if (!tgcred)
 180                 return NULL;
 181 #endif
 182
 183         new = prepare_creds();
 184         if (!new) {
 185                 kfree(tgcred);
 186                 return new;
 187         }
 188
 189 #ifdef CONFIG_KEYS
 190         /* newly exec'd tasks don't get a thread keyring */
 191         key_put(new->thread_keyring);
 192         new->thread_keyring = NULL;
 193
 194         /* create a new per-thread-group creds for all this set of threads to
 195          * share */
 196         memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
 197
 198         atomic_set(&tgcred->usage, 1);
 199         spin_lock_init(&tgcred->lock);
 200
 201         /* inherit the session keyring; new process keyring */
 202         key_get(tgcred->session_keyring);
 203         tgcred->process_keyring = NULL;
 204
 205         release_tgcred(new);
 206         new->tgcred = tgcred;
 207 #endif
 208
 209         return new;
 210 }
 211
 212 /*
 213  * prepare new credentials for the usermode helper dispatcher
 214  */
 215 struct cred *prepare_usermodehelper_creds(void)
 216 {
 217 #ifdef CONFIG_KEYS
 218         struct thread_group_cred *tgcred = NULL;
 219 #endif
 220         struct cred *new;
 221
 222 #ifdef CONFIG_KEYS
 223         tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
 224         if (!tgcred)
 225                 return NULL;
 226 #endif
 227
 228         new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
 229         if (!new)
 230                 return NULL;
 231
 232         memcpy(new, &init_cred, sizeof(struct cred));
 233
 234         atomic_set(&new->usage, 1);
 235         get_group_info(new->group_info);
 236         get_uid(new->user);
 237
 238 #ifdef CONFIG_KEYS
 239         new->thread_keyring = NULL;
 240         new->request_key_auth = NULL;
 241         new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
 242
 243         atomic_set(&tgcred->usage, 1);
 244         spin_lock_init(&tgcred->lock);
 245         new->tgcred = tgcred;
 246 #endif
 247
 248 #ifdef CONFIG_SECURITY
 249         new->security = NULL;
 250 #endif
 251         if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
 252                 goto error;
 253
 254         BUG_ON(atomic_read(&new->usage) != 1);
 255         return new;
 256
 257 error:
 258         put_cred(new);
 259         return NULL;
 260 }
 261
 262 /*
 263  * Copy credentials for the new process created by fork()
 264  *
 265  * We share if we can, but under some circumstances we have to generate a new
 266  * set.
 267  *
 268  * The new process gets the current process's subjective credentials as its
 269  * objective and subjective credentials
 270  */
 271 int copy_creds(struct task_struct *p, unsigned long clone_flags)
 272 {
 273 #ifdef CONFIG_KEYS
 274         struct thread_group_cred *tgcred;
 275 #endif
 276         struct cred *new;
 277
 278         mutex_init(&p->cred_exec_mutex);
 279
 280         if (
 281 #ifdef CONFIG_KEYS
 282                 !p->cred->thread_keyring &&
 283 #endif
 284                 clone_flags & CLONE_THREAD
 285             ) {
 286                 p->real_cred = get_cred(p->cred);
 287                 get_cred(p->cred);
 288                 atomic_inc(&p->cred->user->processes);
 289                 return 0;
 290         }
 291
 292         new = prepare_creds();
 293         if (!new)
 294                 return -ENOMEM;
 295
 296 #ifdef CONFIG_KEYS
 297         /* new threads get their own thread keyrings if their parent already
 298          * had one */
 299         if (new->thread_keyring) {
 300                 key_put(new->thread_keyring);
 301                 new->thread_keyring = NULL;
 302                 if (clone_flags & CLONE_THREAD)
 303                         install_thread_keyring_to_cred(new);
 304         }
 305
 306         /* we share the process and session keyrings between all the threads in
 307          * a process - this is slightly icky as we violate COW credentials a
 308          * bit */
 309         if (!(clone_flags & CLONE_THREAD)) {
 310                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 311                 if (!tgcred) {
 312                         put_cred(new);
 313                         return -ENOMEM;
 314                 }
 315                 atomic_set(&tgcred->usage, 1);
 316                 spin_lock_init(&tgcred->lock);
 317                 tgcred->process_keyring = NULL;
 318                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
 319
 320                 release_tgcred(new);
 321                 new->tgcred = tgcred;
 322         }
 323 #endif
 324
 325         atomic_inc(&new->user->processes);
 326         p->cred = p->real_cred = get_cred(new);
 327         return 0;
 328 }
 329
 330 /**
 331  * commit_creds - Install new credentials upon the current task
 332  * @new: The credentials to be assigned
 333  *
 334  * Install a new set of credentials to the current task, using RCU to replace
 335  * the old set.  Both the objective and the subjective credentials pointers are
 336  * updated.  This function may not be called if the subjective credentials are
 337  * in an overridden state.
 338  *
 339  * This function eats the caller's reference to the new credentials.
 340  *
 341  * Always returns 0 thus allowing this function to be tail-called at the end
 342  * of, say, sys_setgid().
 343  */
 344 int commit_creds(struct cred *new)
 345 {
 346         struct task_struct *task = current;
 347         const struct cred *old;
 348
 349         BUG_ON(task->cred != task->real_cred);
 350         BUG_ON(atomic_read(&task->real_cred->usage) < 2);
 351         BUG_ON(atomic_read(&new->usage) < 1);
 352
 353         old = task->real_cred;
 354         security_commit_creds(new, old);
 355
 356         get_cred(new); /* we will require a ref for the subj creds too */
 357
 358         /* dumpability changes */
 359         if (old->euid != new->euid ||
 360             old->egid != new->egid ||
 361             old->fsuid != new->fsuid ||
 362             old->fsgid != new->fsgid ||
 363             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
 364                 set_dumpable(task->mm, suid_dumpable);
 365                 task->pdeath_signal = 0;
 366                 smp_wmb();
 367         }
 368
 369         /* alter the thread keyring */
 370         if (new->fsuid != old->fsuid)
 371                 key_fsuid_changed(task);
 372         if (new->fsgid != old->fsgid)
 373                 key_fsgid_changed(task);
 374
 375         /* do it
 376          * - What if a process setreuid()'s and this brings the
 377          *   new uid over his NPROC rlimit?  We can check this now
 378          *   cheaply with the new uid cache, so if it matters
 379          *   we should be checking for it.  -DaveM
 380          */
 381         if (new->user != old->user)
 382                 atomic_inc(&new->user->processes);
 383         rcu_assign_pointer(task->real_cred, new);
 384         rcu_assign_pointer(task->cred, new);
 385         if (new->user != old->user)
 386                 atomic_dec(&old->user->processes);
 387
 388         sched_switch_user(task);
 389
 390         /* send notifications */
 391         if (new->uid   != old->uid  ||
 392             new->euid  != old->euid ||
 393             new->suid  != old->suid ||
 394             new->fsuid != old->fsuid)
 395                 proc_id_connector(task, PROC_EVENT_UID);
 396
 397         if (new->gid   != old->gid  ||
 398             new->egid  != old->egid ||
 399             new->sgid  != old->sgid ||
 400             new->fsgid != old->fsgid)
 401                 proc_id_connector(task, PROC_EVENT_GID);
 402
 403         /* release the old obj and subj refs both */
 404         put_cred(old);
 405         put_cred(old);
 406         return 0;
 407 }
 408 EXPORT_SYMBOL(commit_creds);
 409
 410 /**
 411  * abort_creds - Discard a set of credentials and unlock the current task
 412  * @new: The credentials that were going to be applied
 413  *
 414  * Discard a set of credentials that were under construction and unlock the
 415  * current task.
 416  */
 417 void abort_creds(struct cred *new)
 418 {
 419         BUG_ON(atomic_read(&new->usage) < 1);
 420         put_cred(new);
 421 }
 422 EXPORT_SYMBOL(abort_creds);
 423
 424 /**
 425  * override_creds - Override the current process's subjective credentials
 426  * @new: The credentials to be assigned
 427  *
 428  * Install a set of temporary override subjective credentials on the current
 429  * process, returning the old set for later reversion.
 430  */
 431 const struct cred *override_creds(const struct cred *new)
 432 {
 433         const struct cred *old = current->cred;
 434
 435         rcu_assign_pointer(current->cred, get_cred(new));
 436         return old;
 437 }
 438 EXPORT_SYMBOL(override_creds);
 439
 440 /**
 441  * revert_creds - Revert a temporary subjective credentials override
 442  * @old: The credentials to be restored
 443  *
 444  * Revert a temporary set of override subjective credentials to an old set,
 445  * discarding the override set.
 446  */
 447 void revert_creds(const struct cred *old)
 448 {
 449         const struct cred *override = current->cred;
 450
 451         rcu_assign_pointer(current->cred, old);
 452         put_cred(override);
 453 }
 454 EXPORT_SYMBOL(revert_creds);
 455
 456 /*
 457  * initialise the credentials stuff
 458  */
 459 void __init cred_init(void)
 460 {
 461         /* allocate a slab in which we can store credentials */
 462         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
 463                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 464 }
 465
 466 /**
 467  * prepare_kernel_cred - Prepare a set of credentials for a kernel service
 468  * @daemon: A userspace daemon to be used as a reference
 469  *
 470  * Prepare a set of credentials for a kernel service.  This can then be used to
 471  * override a task's own credentials so that work can be done on behalf of that
 472  * task that requires a different subjective context.
 473  *
 474  * @daemon is used to provide a base for the security record, but can be NULL.
 475  * If @daemon is supplied, then the security data will be derived from that;
 476  * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
 477  *
 478  * The caller may change these controls afterwards if desired.
 479  *
 480  * Returns the new credentials or NULL if out of memory.
 481  *
 482  * Does not take, and does not return holding current->cred_replace_mutex.
 483  */
 484 struct cred *prepare_kernel_cred(struct task_struct *daemon)
 485 {
 486         const struct cred *old;
 487         struct cred *new;
 488
 489         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 490         if (!new)
 491                 return NULL;
 492
 493         if (daemon)
 494                 old = get_task_cred(daemon);
 495         else
 496                 old = get_cred(&init_cred);
 497
 498         get_uid(new->user);
 499         get_group_info(new->group_info);
 500
 501 #ifdef CONFIG_KEYS
 502         atomic_inc(&init_tgcred.usage);
 503         new->tgcred = &init_tgcred;
 504         new->request_key_auth = NULL;
 505         new->thread_keyring = NULL;
 506         new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 507 #endif
 508
 509 #ifdef CONFIG_SECURITY
 510         new->security = NULL;
 511 #endif
 512         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 513                 goto error;
 514
 515         atomic_set(&new->usage, 1);
 516         put_cred(old);
 517         return new;
 518
 519 error:
 520         put_cred(new);
 521         return NULL;
 522 }
 523 EXPORT_SYMBOL(prepare_kernel_cred);
 524
 525 /**
 526  * set_security_override - Set the security ID in a set of credentials
 527  * @new: The credentials to alter
 528  * @secid: The LSM security ID to set
 529  *
 530  * Set the LSM security ID in a set of credentials so that the subjective
 531  * security is overridden when an alternative set of credentials is used.
 532  */
 533 int set_security_override(struct cred *new, u32 secid)
 534 {
 535         return security_kernel_act_as(new, secid);
 536 }
 537 EXPORT_SYMBOL(set_security_override);
 538
 539 /**
 540  * set_security_override_from_ctx - Set the security ID in a set of credentials
 541  * @new: The credentials to alter
 542  * @secctx: The LSM security context to generate the security ID from.
 543  *
 544  * Set the LSM security ID in a set of credentials so that the subjective
 545  * security is overridden when an alternative set of credentials is used.  The
 546  * security ID is specified in string form as a security context to be
 547  * interpreted by the LSM.
 548  */
 549 int set_security_override_from_ctx(struct cred *new, const char *secctx)
 550 {
 551         u32 secid;
 552         int ret;
 553
 554         ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
 555         if (ret < 0)
 556                 return ret;
 557
 558         return set_security_override(new, secid);
 559 }
 560 EXPORT_SYMBOL(set_security_override_from_ctx);
 561
 562 /**
 563  * set_create_files_as - Set the LSM file create context in a set of credentials
 564  * @new: The credentials to alter
 565  * @inode: The inode to take the context from
 566  *
 567  * Change the LSM file creation context in a set of credentials to be the same
 568  * as the object context of the specified inode, so that the new inodes have
 569  * the same MAC context as that inode.
 570  */
 571 int set_create_files_as(struct cred *new, struct inode *inode)
 572 {
 573         new->fsuid = inode->i_uid;
 574         new->fsgid = inode->i_gid;
 575         return security_kernel_create_files_as(new, inode);
 576 }
 577 EXPORT_SYMBOL(set_create_files_as);