kernel/cred.c

   1 /* Task credentials management
   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(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 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 new credentials for the usermode helper dispatcher
 168  */
 169 struct cred *prepare_usermodehelper_creds(void)
 170 {
 171 #ifdef CONFIG_KEYS
 172         struct thread_group_cred *tgcred = NULL;
 173 #endif
 174         struct cred *new;
 175
 176 #ifdef CONFIG_KEYS
 177         tgcred = kzalloc(sizeof(*new->tgcred), GFP_ATOMIC);
 178         if (!tgcred)
 179                 return NULL;
 180 #endif
 181
 182         new = kmem_cache_alloc(cred_jar, GFP_ATOMIC);
 183         if (!new)
 184                 return NULL;
 185
 186         memcpy(new, &init_cred, sizeof(struct cred));
 187
 188         atomic_set(&new->usage, 1);
 189         get_group_info(new->group_info);
 190         get_uid(new->user);
 191
 192 #ifdef CONFIG_KEYS
 193         new->thread_keyring = NULL;
 194         new->request_key_auth = NULL;
 195         new->jit_keyring = KEY_REQKEY_DEFL_DEFAULT;
 196
 197         atomic_set(&tgcred->usage, 1);
 198         spin_lock_init(&tgcred->lock);
 199         new->tgcred = tgcred;
 200 #endif
 201
 202 #ifdef CONFIG_SECURITY
 203         new->security = NULL;
 204 #endif
 205         if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
 206                 goto error;
 207
 208         BUG_ON(atomic_read(&new->usage) != 1);
 209         return new;
 210
 211 error:
 212         put_cred(new);
 213         return NULL;
 214 }
 215
 216 /*
 217  * Copy credentials for the new process created by fork()
 218  *
 219  * We share if we can, but under some circumstances we have to generate a new
 220  * set.
 221  */
 222 int copy_creds(struct task_struct *p, unsigned long clone_flags)
 223 {
 224 #ifdef CONFIG_KEYS
 225         struct thread_group_cred *tgcred;
 226 #endif
 227         struct cred *new;
 228
 229         mutex_init(&p->cred_exec_mutex);
 230
 231         if (
 232 #ifdef CONFIG_KEYS
 233                 !p->cred->thread_keyring &&
 234 #endif
 235                 clone_flags & CLONE_THREAD
 236             ) {
 237                 get_cred(p->cred);
 238                 atomic_inc(&p->cred->user->processes);
 239                 return 0;
 240         }
 241
 242         new = prepare_creds();
 243         if (!new)
 244                 return -ENOMEM;
 245
 246 #ifdef CONFIG_KEYS
 247         /* new threads get their own thread keyrings if their parent already
 248          * had one */
 249         if (new->thread_keyring) {
 250                 key_put(new->thread_keyring);
 251                 new->thread_keyring = NULL;
 252                 if (clone_flags & CLONE_THREAD)
 253                         install_thread_keyring_to_cred(new);
 254         }
 255
 256         /* we share the process and session keyrings between all the threads in
 257          * a process - this is slightly icky as we violate COW credentials a
 258          * bit */
 259         if (!(clone_flags & CLONE_THREAD)) {
 260                 tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 261                 if (!tgcred) {
 262                         put_cred(new);
 263                         return -ENOMEM;
 264                 }
 265                 atomic_set(&tgcred->usage, 1);
 266                 spin_lock_init(&tgcred->lock);
 267                 tgcred->process_keyring = NULL;
 268                 tgcred->session_keyring = key_get(new->tgcred->session_keyring);
 269
 270                 release_tgcred(new);
 271                 new->tgcred = tgcred;
 272         }
 273 #endif
 274
 275         atomic_inc(&new->user->processes);
 276         p->cred = new;
 277         return 0;
 278 }
 279
 280 /**
 281  * commit_creds - Install new credentials upon the current task
 282  * @new: The credentials to be assigned
 283  *
 284  * Install a new set of credentials to the current task, using RCU to replace
 285  * the old set.
 286  *
 287  * This function eats the caller's reference to the new credentials.
 288  *
 289  * Always returns 0 thus allowing this function to be tail-called at the end
 290  * of, say, sys_setgid().
 291  */
 292 int commit_creds(struct cred *new)
 293 {
 294         struct task_struct *task = current;
 295         const struct cred *old;
 296
 297         BUG_ON(atomic_read(&new->usage) < 1);
 298         BUG_ON(atomic_read(&task->cred->usage) < 1);
 299
 300         old = task->cred;
 301         security_commit_creds(new, old);
 302
 303         /* dumpability changes */
 304         if (old->euid != new->euid ||
 305             old->egid != new->egid ||
 306             old->fsuid != new->fsuid ||
 307             old->fsgid != new->fsgid ||
 308             !cap_issubset(new->cap_permitted, old->cap_permitted)) {
 309                 set_dumpable(task->mm, suid_dumpable);
 310                 task->pdeath_signal = 0;
 311                 smp_wmb();
 312         }
 313
 314         /* alter the thread keyring */
 315         if (new->fsuid != old->fsuid)
 316                 key_fsuid_changed(task);
 317         if (new->fsgid != old->fsgid)
 318                 key_fsgid_changed(task);
 319
 320         /* do it
 321          * - What if a process setreuid()'s and this brings the
 322          *   new uid over his NPROC rlimit?  We can check this now
 323          *   cheaply with the new uid cache, so if it matters
 324          *   we should be checking for it.  -DaveM
 325          */
 326         if (new->user != old->user)
 327                 atomic_inc(&new->user->processes);
 328         rcu_assign_pointer(task->cred, new);
 329         if (new->user != old->user)
 330                 atomic_dec(&old->user->processes);
 331
 332         sched_switch_user(task);
 333
 334         /* send notifications */
 335         if (new->uid   != old->uid  ||
 336             new->euid  != old->euid ||
 337             new->suid  != old->suid ||
 338             new->fsuid != old->fsuid)
 339                 proc_id_connector(task, PROC_EVENT_UID);
 340
 341         if (new->gid   != old->gid  ||
 342             new->egid  != old->egid ||
 343             new->sgid  != old->sgid ||
 344             new->fsgid != old->fsgid)
 345                 proc_id_connector(task, PROC_EVENT_GID);
 346
 347         put_cred(old);
 348         return 0;
 349 }
 350 EXPORT_SYMBOL(commit_creds);
 351
 352 /**
 353  * abort_creds - Discard a set of credentials and unlock the current task
 354  * @new: The credentials that were going to be applied
 355  *
 356  * Discard a set of credentials that were under construction and unlock the
 357  * current task.
 358  */
 359 void abort_creds(struct cred *new)
 360 {
 361         BUG_ON(atomic_read(&new->usage) < 1);
 362         put_cred(new);
 363 }
 364 EXPORT_SYMBOL(abort_creds);
 365
 366 /**
 367  * override_creds - Temporarily override the current process's credentials
 368  * @new: The credentials to be assigned
 369  *
 370  * Install a set of temporary override credentials on the current process,
 371  * returning the old set for later reversion.
 372  */
 373 const struct cred *override_creds(const struct cred *new)
 374 {
 375         const struct cred *old = current->cred;
 376
 377         rcu_assign_pointer(current->cred, get_cred(new));
 378         return old;
 379 }
 380 EXPORT_SYMBOL(override_creds);
 381
 382 /**
 383  * revert_creds - Revert a temporary credentials override
 384  * @old: The credentials to be restored
 385  *
 386  * Revert a temporary set of override credentials to an old set, discarding the
 387  * override set.
 388  */
 389 void revert_creds(const struct cred *old)
 390 {
 391         const struct cred *override = current->cred;
 392
 393         rcu_assign_pointer(current->cred, old);
 394         put_cred(override);
 395 }
 396 EXPORT_SYMBOL(revert_creds);
 397
 398 /*
 399  * initialise the credentials stuff
 400  */
 401 void __init cred_init(void)
 402 {
 403         /* allocate a slab in which we can store credentials */
 404         cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
 405                                      0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 406 }