linux/kernel/cred.c
<<
>>
Prefs
   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
  21static struct kmem_cache *cred_jar;
  22
  23/*
  24 * The common credentials for the initial task's thread group
  25 */
  26#ifdef CONFIG_KEYS
  27static 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 */
  37struct 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
  55static 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 */
  71static 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 */
  84static 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 */
 107void __put_cred(struct cred *cred)
 108{
 109        BUG_ON(atomic_read(&cred->usage) != 0);
 110
 111        call_rcu(&cred->rcu, put_cred_rcu);
 112}
 113EXPORT_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 */
 129struct 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
 162error:
 163        abort_creds(new);
 164        return NULL;
 165}
 166EXPORT_SYMBOL(prepare_creds);
 167
 168/*
 169 * Prepare credentials for current to perform an execve()
 170 * - The caller must hold current->cred_exec_mutex
 171 */
 172struct 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 */
 215struct 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
 257error:
 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 */
 271int 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        int ret;
 278
 279        mutex_init(&p->cred_exec_mutex);
 280
 281        if (
 282#ifdef CONFIG_KEYS
 283                !p->cred->thread_keyring &&
 284#endif
 285                clone_flags & CLONE_THREAD
 286            ) {
 287                p->real_cred = get_cred(p->cred);
 288                get_cred(p->cred);
 289                atomic_inc(&p->cred->user->processes);
 290                return 0;
 291        }
 292
 293        new = prepare_creds();
 294        if (!new)
 295                return -ENOMEM;
 296
 297        if (clone_flags & CLONE_NEWUSER) {
 298                ret = create_user_ns(new);
 299                if (ret < 0)
 300                        goto error_put;
 301        }
 302
 303#ifdef CONFIG_KEYS
 304        /* new threads get their own thread keyrings if their parent already
 305         * had one */
 306        if (new->thread_keyring) {
 307                key_put(new->thread_keyring);
 308                new->thread_keyring = NULL;
 309                if (clone_flags & CLONE_THREAD)
 310                        install_thread_keyring_to_cred(new);
 311        }
 312
 313        /* we share the process and session keyrings between all the threads in
 314         * a process - this is slightly icky as we violate COW credentials a
 315         * bit */
 316        if (!(clone_flags & CLONE_THREAD)) {
 317                tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
 318                if (!tgcred) {
 319                        ret = -ENOMEM;
 320                        goto error_put;
 321                }
 322                atomic_set(&tgcred->usage, 1);
 323                spin_lock_init(&tgcred->lock);
 324                tgcred->process_keyring = NULL;
 325                tgcred->session_keyring = key_get(new->tgcred->session_keyring);
 326
 327                release_tgcred(new);
 328                new->tgcred = tgcred;
 329        }
 330#endif
 331
 332        atomic_inc(&new->user->processes);
 333        p->cred = p->real_cred = get_cred(new);
 334        return 0;
 335
 336error_put:
 337        put_cred(new);
 338        return ret;
 339}
 340
 341/**
 342 * commit_creds - Install new credentials upon the current task
 343 * @new: The credentials to be assigned
 344 *
 345 * Install a new set of credentials to the current task, using RCU to replace
 346 * the old set.  Both the objective and the subjective credentials pointers are
 347 * updated.  This function may not be called if the subjective credentials are
 348 * in an overridden state.
 349 *
 350 * This function eats the caller's reference to the new credentials.
 351 *
 352 * Always returns 0 thus allowing this function to be tail-called at the end
 353 * of, say, sys_setgid().
 354 */
 355int commit_creds(struct cred *new)
 356{
 357        struct task_struct *task = current;
 358        const struct cred *old;
 359
 360        BUG_ON(task->cred != task->real_cred);
 361        BUG_ON(atomic_read(&task->real_cred->usage) < 2);
 362        BUG_ON(atomic_read(&new->usage) < 1);
 363
 364        old = task->real_cred;
 365        security_commit_creds(new, old);
 366
 367        get_cred(new); /* we will require a ref for the subj creds too */
 368
 369        /* dumpability changes */
 370        if (old->euid != new->euid ||
 371            old->egid != new->egid ||
 372            old->fsuid != new->fsuid ||
 373            old->fsgid != new->fsgid ||
 374            !cap_issubset(new->cap_permitted, old->cap_permitted)) {
 375                if (task->mm)
 376                        set_dumpable(task->mm, suid_dumpable);
 377                task->pdeath_signal = 0;
 378                smp_wmb();
 379        }
 380
 381        /* alter the thread keyring */
 382        if (new->fsuid != old->fsuid)
 383                key_fsuid_changed(task);
 384        if (new->fsgid != old->fsgid)
 385                key_fsgid_changed(task);
 386
 387        /* do it
 388         * - What if a process setreuid()'s and this brings the
 389         *   new uid over his NPROC rlimit?  We can check this now
 390         *   cheaply with the new uid cache, so if it matters
 391         *   we should be checking for it.  -DaveM
 392         */
 393        if (new->user != old->user)
 394                atomic_inc(&new->user->processes);
 395        rcu_assign_pointer(task->real_cred, new);
 396        rcu_assign_pointer(task->cred, new);
 397        if (new->user != old->user)
 398                atomic_dec(&old->user->processes);
 399
 400        sched_switch_user(task);
 401
 402        /* send notifications */
 403        if (new->uid   != old->uid  ||
 404            new->euid  != old->euid ||
 405            new->suid  != old->suid ||
 406            new->fsuid != old->fsuid)
 407                proc_id_connector(task, PROC_EVENT_UID);
 408
 409        if (new->gid   != old->gid  ||
 410            new->egid  != old->egid ||
 411            new->sgid  != old->sgid ||
 412            new->fsgid != old->fsgid)
 413                proc_id_connector(task, PROC_EVENT_GID);
 414
 415        /* release the old obj and subj refs both */
 416        put_cred(old);
 417        put_cred(old);
 418        return 0;
 419}
 420EXPORT_SYMBOL(commit_creds);
 421
 422/**
 423 * abort_creds - Discard a set of credentials and unlock the current task
 424 * @new: The credentials that were going to be applied
 425 *
 426 * Discard a set of credentials that were under construction and unlock the
 427 * current task.
 428 */
 429void abort_creds(struct cred *new)
 430{
 431        BUG_ON(atomic_read(&new->usage) < 1);
 432        put_cred(new);
 433}
 434EXPORT_SYMBOL(abort_creds);
 435
 436/**
 437 * override_creds - Override the current process's subjective credentials
 438 * @new: The credentials to be assigned
 439 *
 440 * Install a set of temporary override subjective credentials on the current
 441 * process, returning the old set for later reversion.
 442 */
 443const struct cred *override_creds(const struct cred *new)
 444{
 445        const struct cred *old = current->cred;
 446
 447        rcu_assign_pointer(current->cred, get_cred(new));
 448        return old;
 449}
 450EXPORT_SYMBOL(override_creds);
 451
 452/**
 453 * revert_creds - Revert a temporary subjective credentials override
 454 * @old: The credentials to be restored
 455 *
 456 * Revert a temporary set of override subjective credentials to an old set,
 457 * discarding the override set.
 458 */
 459void revert_creds(const struct cred *old)
 460{
 461        const struct cred *override = current->cred;
 462
 463        rcu_assign_pointer(current->cred, old);
 464        put_cred(override);
 465}
 466EXPORT_SYMBOL(revert_creds);
 467
 468/*
 469 * initialise the credentials stuff
 470 */
 471void __init cred_init(void)
 472{
 473        /* allocate a slab in which we can store credentials */
 474        cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
 475                                     0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 476}
 477
 478/**
 479 * prepare_kernel_cred - Prepare a set of credentials for a kernel service
 480 * @daemon: A userspace daemon to be used as a reference
 481 *
 482 * Prepare a set of credentials for a kernel service.  This can then be used to
 483 * override a task's own credentials so that work can be done on behalf of that
 484 * task that requires a different subjective context.
 485 *
 486 * @daemon is used to provide a base for the security record, but can be NULL.
 487 * If @daemon is supplied, then the security data will be derived from that;
 488 * otherwise they'll be set to 0 and no groups, full capabilities and no keys.
 489 *
 490 * The caller may change these controls afterwards if desired.
 491 *
 492 * Returns the new credentials or NULL if out of memory.
 493 *
 494 * Does not take, and does not return holding current->cred_replace_mutex.
 495 */
 496struct cred *prepare_kernel_cred(struct task_struct *daemon)
 497{
 498        const struct cred *old;
 499        struct cred *new;
 500
 501        new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
 502        if (!new)
 503                return NULL;
 504
 505        if (daemon)
 506                old = get_task_cred(daemon);
 507        else
 508                old = get_cred(&init_cred);
 509
 510        *new = *old;
 511        get_uid(new->user);
 512        get_group_info(new->group_info);
 513
 514#ifdef CONFIG_KEYS
 515        atomic_inc(&init_tgcred.usage);
 516        new->tgcred = &init_tgcred;
 517        new->request_key_auth = NULL;
 518        new->thread_keyring = NULL;
 519        new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
 520#endif
 521
 522#ifdef CONFIG_SECURITY
 523        new->security = NULL;
 524#endif
 525        if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
 526                goto error;
 527
 528        atomic_set(&new->usage, 1);
 529        put_cred(old);
 530        return new;
 531
 532error:
 533        put_cred(new);
 534        put_cred(old);
 535        return NULL;
 536}
 537EXPORT_SYMBOL(prepare_kernel_cred);
 538
 539/**
 540 * set_security_override - Set the security ID in a set of credentials
 541 * @new: The credentials to alter
 542 * @secid: The LSM security ID to set
 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.
 546 */
 547int set_security_override(struct cred *new, u32 secid)
 548{
 549        return security_kernel_act_as(new, secid);
 550}
 551EXPORT_SYMBOL(set_security_override);
 552
 553/**
 554 * set_security_override_from_ctx - Set the security ID in a set of credentials
 555 * @new: The credentials to alter
 556 * @secctx: The LSM security context to generate the security ID from.
 557 *
 558 * Set the LSM security ID in a set of credentials so that the subjective
 559 * security is overridden when an alternative set of credentials is used.  The
 560 * security ID is specified in string form as a security context to be
 561 * interpreted by the LSM.
 562 */
 563int set_security_override_from_ctx(struct cred *new, const char *secctx)
 564{
 565        u32 secid;
 566        int ret;
 567
 568        ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
 569        if (ret < 0)
 570                return ret;
 571
 572        return set_security_override(new, secid);
 573}
 574EXPORT_SYMBOL(set_security_override_from_ctx);
 575
 576/**
 577 * set_create_files_as - Set the LSM file create context in a set of credentials
 578 * @new: The credentials to alter
 579 * @inode: The inode to take the context from
 580 *
 581 * Change the LSM file creation context in a set of credentials to be the same
 582 * as the object context of the specified inode, so that the new inodes have
 583 * the same MAC context as that inode.
 584 */
 585int set_create_files_as(struct cred *new, struct inode *inode)
 586{
 587        new->fsuid = inode->i_uid;
 588        new->fsgid = inode->i_gid;
 589        return security_kernel_create_files_as(new, inode);
 590}
 591EXPORT_SYMBOL(set_create_files_as);
 592