kernel/cred.c

   1 /* Task credentials management
   2  *
   3  * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells ([email protected])
   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(3),
  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  * Returns a pointer to the new creds-to-be if successful, NULL otherwise.
 124  *
 125  * Call commit_creds() or abort_creds() to clean up.
 126  */
 127 struct cred *prepare_creds(void)
 128 {
 129         struct task_struct *task = current;
 130         const struct cred *old;
 131         struct cred *new;
 132
 133         BUG_ON(atomic_read(&task->cred->usage) < 1);
 134
 135         new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 136         if (!new)
 137                 return NULL;
 138
 139         old = task->cred;
 140         memcpy(new, old, sizeof(struct cred));
 141
 142         atomic_set(&new->usage, 1);
 143         get_group_info(new->group_info);
 144         get_uid(new->user);
 145
 146 #ifdef CONFIG_KEYS
 147         key_get(new->thread_keyring);
 148         key_get(new->request_key_auth);
 149         atomic_inc(&new->tgcred->usage);
 150 #endif
 151
 152 #ifdef CONFIG_SECURITY
 153         new->security = NULL;
 154 #endif
 155
 156         if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 157                 goto error;
 158         return new;
 159
 160 error:
 161         abort_creds(new);
 162         return NULL;
 163 }
 164 EXPORT_SYMBOL(prepare_creds);
 165
 166 /*
 167  * Prepare credentials for current to perform an execve()
 168  * - The caller must hold current->cred_exec_mutex
 169  */
 170 struct cred *prepare_exec_creds(void)
 171 {
 172         struct thread_group_cred *tgcred = NULL;
 173         struct cred *new;
 174
 175 #ifdef CONFIG_KEYS
 176         tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 177         if (!tgcred)
 178                 return NULL;
 179 #endif
 180
 181         new = prepare_creds();
 182         if (!new) {
 183                 kfree(tgcred);
 184                 return new;
 185         }
 186
 187 #ifdef CONFIG_KEYS
 188         /* newly exec'd tasks don't get a thread keyring */
 189         key_put(new->thread_keyring);
 190         new->thread_keyring = NULL;
 191
 192         /* create a new per-thread-group creds for all this set of threads to
 193          * share */
 194         memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));
 195
 196         atomic_set(&tgcred->usage, 1);
 197         spin_lock_init(&tgcred->lock);
 198
 199         /* inherit the session keyring; new process keyring */
 200         key_get(tgcred->session_keyring);
 201         tgcred->process_keyring = NULL;
 202
 203         release_tgcred(new);
 204         new->tgcred = tgcred;
 205 #endif
 206
 207         return new;
 208 }
 209
 210 /*
 211  * prepare new credentials for the usermode helper dispatcher
 212  */
 213 struct cred *prepare_usermodehelper_creds(void)
 214 {
 215 #ifdef CONFIG_KEYS
 216         struct thread_group_cred *tgcred = NULL;
 217 #endif
 218         struct cred *new;
 219
 220 #ifdef CONFIG_KEYS
 221         tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
 222         if (!tgcred)
 223                 return NULL;
 224 #endif
 225
 226         new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
 227         if (!new)
 228                 return NULL;
 229
 230         memcpy(new, &init_cred, sizeof(struct cred));
 231
 232         atomic_set(&new->usage, 1);
 233         get_group_info(new->group_info);
 234         get_uid(new->user);
 235
 236 #ifdef CONFIG_KEYS
 237         new->thread_keyring = NULL;
 238         new->request_key_auth = NULL;
 239         new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
 240
 241         atomic_set(&tgcred->usage, 1);
 242         spin_lock_init(&tgcred->lock);
 243         new->tgcred = tgcred;
 244 #endif
 245
 246 #ifdef CONFIG_SECURITY
 247         new->security = NULL;
 248 #endif
 249         if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
 250                 goto error;
 251
 252         BUG_ON(atomic_read(&new->usage) != 1);
 253         return new;
 254
 255 error:
 256         put_cred(new);
 257         return NULL;
 258 }
 259
 260 /*
 261  * Copy credentials for the new process created by fork()
 262  *
 263  * We share if we can, but under some circumstances we have to generate a new
 264  * set.
 265  */
 266 int copy_creds(struct task_struct *p, unsigned long clone_flags)
 267 {
 268 #ifdef CONFIG_KEYS
 269         struct thread_group_cred *tgcred;
 270 #endif
 271         struct cred *new;
 272
 273         mutex_init(&p->cred_exec_mutex);
 274
 275         if (
 276 #ifdef CONFIG_KEYS
 277                 !p->cred->thread_keyring &&
 278 #endif
 279                 clone_flags & CLONE_THREAD
 280             ) {
 281                 get_cred(p->cred);
 282                 atomic_inc(&p->cred->user->processes);
 283                 return 0;
 284         }
 285
 286         new = prepare_creds();
 287         if (!new)
 288                 return -ENOMEM;
 289
 290 #ifdef CONFIG_KEYS
 291         /* new threads get their own thread keyrings if their parent already
 292          * had one */
 293         if (new->thread_keyring) {
 294                 key_put(new->thread_keyring);
 295                 new->thread_keyring = NULL;
 296                 if (clone_flags & CLONE_THREAD)
 297                         install_thread_keyring_to_cred(new);
 298         }
 299
 300         /* we share the process and session keyrings between all the threads in
 301          * a process - this is slightly icky as we violate COW credentials a
 302          * bit */
 303         if (!(clone_flags & CLONE_THREAD)) {
 304                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 305                 if (!tgcred) {
 306                         put_cred(new);
 307                         return -ENOMEM;
 308                 }
 309                 atomic_set(&tgcred->usage, 1);
 310                 spin_lock_init(&tgcred->lock);
 311                 tgcred->process_keyring = NULL;
 312                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
 313
 314                 release_tgcred(new);
 315                 new->tgcred = tgcred;
 316         }
 317 #endif
 318
 319         atomic_inc(&new->user->processes);
 320         p->cred = new;
 321         return 0;
 322 }
 323
 324 /**
 325  * commit_creds - Install new credentials upon the current task
 326  * @new: The credentials to be assigned
 327  *
 328  * Install a new set of credentials to the current task, using RCU to replace
 329  * the old set.
 330  *
 331  * This function eats the caller's reference to the new credentials.
 332  *
 333  * Always returns 0 thus allowing this function to be tail-called at the end
 334  * of, say, sys_setgid().
 335  */
 336 int commit_creds(struct cred *new)
 337 {
 338         struct task_struct *task = current;
 339         const struct cred *old;
 340
 341         BUG_ON(atomic_read(&new->usage) < 1);
 342         BUG_ON(atomic_read(&task->cred->usage) < 1);
 343
 344         old = task->cred;
 345         security_commit_creds(new, old);
 346
 347         /* dumpability changes */
 348         if (old->euid != new->euid ||
 349             old->egid != new->egid ||
 350             old->fsuid != new->fsuid ||
 351             old->fsgid != new->fsgid ||
 352             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
 353                 set_dumpable(task->mm, suid_dumpable);
 354                 task->pdeath_signal = 0;
 355                 smp_wmb();
 356         }
 357
 358         /* alter the thread keyring */
 359         if (new->fsuid != old->fsuid)
 360                 key_fsuid_changed(task);
 361         if (new->fsgid != old->fsgid)
 362                 key_fsgid_changed(task);
 363
 364         /* do it
 365          * - What if a process setreuid()'s and this brings the
 366          *   new uid over his NPROC rlimit?  We can check this now
 367          *   cheaply with the new uid cache, so if it matters
 368          *   we should be checking for it.  -DaveM
 369          */
 370         if (new->user != old->user)
 371                 atomic_inc(&new->user->processes);
 372         rcu_assign_pointer(task->cred, new);
 373         if (new->user != old->user)
 374                 atomic_dec(&old->user->processes);
 375
 376         sched_switch_user(task);
 377
 378         /* send notifications */
 379         if (new->uid   != old->uid  ||
 380             new->euid  != old->euid ||
 381             new->suid  != old->suid ||
 382             new->fsuid != old->fsuid)
 383                 proc_id_connector(task, PROC_EVENT_UID);
 384
 385         if (new->gid   != old->gid  ||
 386             new->egid  != old->egid ||
 387             new->sgid  != old->sgid ||
 388             new->fsgid != old->fsgid)
 389                 proc_id_connector(task, PROC_EVENT_GID);
 390
 391         put_cred(old);
 392         return 0;
 393 }
 394 EXPORT_SYMBOL(commit_creds);
 395
 396 /**
 397  * abort_creds - Discard a set of credentials and unlock the current task
 398  * @new: The credentials that were going to be applied
 399  *
 400  * Discard a set of credentials that were under construction and unlock the
 401  * current task.
 402  */
 403 void abort_creds(struct cred *new)
 404 {
 405         BUG_ON(atomic_read(&new->usage) < 1);
 406         put_cred(new);
 407 }
 408 EXPORT_SYMBOL(abort_creds);
 409
 410 /**
 411  * override_creds - Temporarily override the current process's credentials
 412  * @new: The credentials to be assigned
 413  *
 414  * Install a set of temporary override credentials on the current process,
 415  * returning the old set for later reversion.
 416  */
 417 const struct cred *override_creds(const struct cred *new)
 418 {
 419         const struct cred *old = current->cred;
 420
 421         rcu_assign_pointer(current->cred, get_cred(new));
 422         return old;
 423 }
 424 EXPORT_SYMBOL(override_creds);
 425
 426 /**
 427  * revert_creds - Revert a temporary credentials override
 428  * @old: The credentials to be restored
 429  *
 430  * Revert a temporary set of override credentials to an old set, discarding the
 431  * override set.
 432  */
 433 void revert_creds(const struct cred *old)
 434 {
 435         const struct cred *override = current->cred;
 436
 437         rcu_assign_pointer(current->cred, old);
 438         put_cred(override);
 439 }
 440 EXPORT_SYMBOL(revert_creds);
 441
 442 /*
 443  * initialise the credentials stuff
 444  */
 445 void __init cred_init(void)
 446 {
 447         /* allocate a slab in which we can store credentials */
 448         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
 449                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 450 }