security/keys/process_keys.c

   1 /* Manage a process's keyrings
   2  *
   3  * Copyright (C) 2004-2005, 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 License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/init.h>
  14 #include <linux/sched.h>
  15 #include <linux/keyctl.h>
  16 #include <linux/fs.h>
  17 #include <linux/err.h>
  18 #include <linux/mutex.h>
  19 #include <linux/security.h>
  20 #include <linux/user_namespace.h>
  21 #include <asm/uaccess.h>
  22 #include "internal.h"
  23
  24 /* Session keyring create vs join semaphore */
  25 static DEFINE_MUTEX(key_session_mutex);
  26
  27 /* User keyring creation semaphore */
  28 static DEFINE_MUTEX(key_user_keyring_mutex);
  29
  30 /* The root user's tracking struct */
  31 struct key_user root_key_user = {
  32         .usage          = ATOMIC_INIT(3),
  33         .cons_lock      = __MUTEX_INITIALIZER(root_key_user.cons_lock),
  34         .lock           = __SPIN_LOCK_UNLOCKED(root_key_user.lock),
  35         .nkeys          = ATOMIC_INIT(2),
  36         .nikeys         = ATOMIC_INIT(2),
  37         .uid            = GLOBAL_ROOT_UID,
  38 };
  39
  40 /*
  41  * Install the user and user session keyrings for the current process's UID.
  42  */
  43 int install_user_keyrings(void)
  44 {
  45         struct user_struct *user;
  46         const struct cred *cred;
  47         struct key *uid_keyring, *session_keyring;
  48         char buf[20];
  49         int ret;
  50         uid_t uid;
  51
  52         cred = current_cred();
  53         user = cred->user;
  54         uid = from_kuid(cred->user_ns, user->uid);
  55
  56         kenter("%p{%u}", user, uid);
  57
  58         if (user->uid_keyring) {
  59                 kleave(" = 0 [exist]");
  60                 return 0;
  61         }
  62
  63         mutex_lock(&key_user_keyring_mutex);
  64         ret = 0;
  65
  66         if (!user->uid_keyring) {
  67                 /* get the UID-specific keyring
  68                  * - there may be one in existence already as it may have been
  69                  *   pinned by a session, but the user_struct pointing to it
  70                  *   may have been destroyed by setuid */
  71                 sprintf(buf, "_uid.%u", uid);
  72
  73                 uid_keyring = find_keyring_by_name(buf, true);
  74                 if (IS_ERR(uid_keyring)) {
  75                         uid_keyring = keyring_alloc(buf, user->uid, INVALID_GID,
  76                                                     cred, KEY_ALLOC_IN_QUOTA,
  77                                                     NULL);
  78                         if (IS_ERR(uid_keyring)) {
  79                                 ret = PTR_ERR(uid_keyring);
  80                                 goto error;
  81                         }
  82                 }
  83
  84                 /* get a default session keyring (which might also exist
  85                  * already) */
  86                 sprintf(buf, "_uid_ses.%u", uid);
  87
  88                 session_keyring = find_keyring_by_name(buf, true);
  89                 if (IS_ERR(session_keyring)) {
  90                         session_keyring =
  91                                 keyring_alloc(buf, user->uid, INVALID_GID,
  92                                               cred, KEY_ALLOC_IN_QUOTA, NULL);
  93                         if (IS_ERR(session_keyring)) {
  94                                 ret = PTR_ERR(session_keyring);
  95                                 goto error_release;
  96                         }
  97
  98                         /* we install a link from the user session keyring to
  99                          * the user keyring */
 100                         ret = key_link(session_keyring, uid_keyring);
 101                         if (ret < 0)
 102                                 goto error_release_both;
 103                 }
 104
 105                 /* install the keyrings */
 106                 user->uid_keyring = uid_keyring;
 107                 user->session_keyring = session_keyring;
 108         }
 109
 110         mutex_unlock(&key_user_keyring_mutex);
 111         kleave(" = 0");
 112         return 0;
 113
 114 error_release_both:
 115         key_put(session_keyring);
 116 error_release:
 117         key_put(uid_keyring);
 118 error:
 119         mutex_unlock(&key_user_keyring_mutex);
 120         kleave(" = %d", ret);
 121         return ret;
 122 }
 123
 124 /*
 125  * Install a fresh thread keyring directly to new credentials.  This keyring is
 126  * allowed to overrun the quota.
 127  */
 128 int install_thread_keyring_to_cred(struct cred *new)
 129 {
 130         struct key *keyring;
 131
 132         keyring = keyring_alloc("_tid", new->uid, new->gid, new,
 133                                 KEY_ALLOC_QUOTA_OVERRUN, NULL);
 134         if (IS_ERR(keyring))
 135                 return PTR_ERR(keyring);
 136
 137         new->thread_keyring = keyring;
 138         return 0;
 139 }
 140
 141 /*
 142  * Install a fresh thread keyring, discarding the old one.
 143  */
 144 static int install_thread_keyring(void)
 145 {
 146         struct cred *new;
 147         int ret;
 148
 149         new = prepare_creds();
 150         if (!new)
 151                 return -ENOMEM;
 152
 153         BUG_ON(new->thread_keyring);
 154
 155         ret = install_thread_keyring_to_cred(new);
 156         if (ret < 0) {
 157                 abort_creds(new);
 158                 return ret;
 159         }
 160
 161         return commit_creds(new);
 162 }
 163
 164 /*
 165  * Install a process keyring directly to a credentials struct.
 166  *
 167  * Returns -EEXIST if there was already a process keyring, 0 if one installed,
 168  * and other value on any other error
 169  */
 170 int install_process_keyring_to_cred(struct cred *new)
 171 {
 172         struct key *keyring;
 173         int ret;
 174
 175         if (new->tgcred->process_keyring)
 176                 return -EEXIST;
 177
 178         keyring = keyring_alloc("_pid", new->uid, new->gid,
 179                                 new, KEY_ALLOC_QUOTA_OVERRUN, NULL);
 180         if (IS_ERR(keyring))
 181                 return PTR_ERR(keyring);
 182
 183         spin_lock_irq(&new->tgcred->lock);
 184         if (!new->tgcred->process_keyring) {
 185                 new->tgcred->process_keyring = keyring;
 186                 keyring = NULL;
 187                 ret = 0;
 188         } else {
 189                 ret = -EEXIST;
 190         }
 191         spin_unlock_irq(&new->tgcred->lock);
 192         key_put(keyring);
 193         return ret;
 194 }
 195
 196 /*
 197  * Make sure a process keyring is installed for the current process.  The
 198  * existing process keyring is not replaced.
 199  *
 200  * Returns 0 if there is a process keyring by the end of this function, some
 201  * error otherwise.
 202  */
 203 static int install_process_keyring(void)
 204 {
 205         struct cred *new;
 206         int ret;
 207
 208         new = prepare_creds();
 209         if (!new)
 210                 return -ENOMEM;
 211
 212         ret = install_process_keyring_to_cred(new);
 213         if (ret < 0) {
 214                 abort_creds(new);
 215                 return ret != -EEXIST ? ret : 0;
 216         }
 217
 218         return commit_creds(new);
 219 }
 220
 221 /*
 222  * Install a session keyring directly to a credentials struct.
 223  */
 224 int install_session_keyring_to_cred(struct cred *cred, struct key *keyring)
 225 {
 226         unsigned long flags;
 227         struct key *old;
 228
 229         might_sleep();
 230
 231         /* create an empty session keyring */
 232         if (!keyring) {
 233                 flags = KEY_ALLOC_QUOTA_OVERRUN;
 234                 if (cred->tgcred->session_keyring)
 235                         flags = KEY_ALLOC_IN_QUOTA;
 236
 237                 keyring = keyring_alloc("_ses", cred->uid, cred->gid,
 238                                         cred, flags, NULL);
 239                 if (IS_ERR(keyring))
 240                         return PTR_ERR(keyring);
 241         } else {
 242                 atomic_inc(&keyring->usage);
 243         }
 244
 245         /* install the keyring */
 246         spin_lock_irq(&cred->tgcred->lock);
 247         old = cred->tgcred->session_keyring;
 248         rcu_assign_pointer(cred->tgcred->session_keyring, keyring);
 249         spin_unlock_irq(&cred->tgcred->lock);
 250
 251         /* we're using RCU on the pointer, but there's no point synchronising
 252          * on it if it didn't previously point to anything */
 253         if (old) {
 254                 synchronize_rcu();
 255                 key_put(old);
 256         }
 257
 258         return 0;
 259 }
 260
 261 /*
 262  * Install a session keyring, discarding the old one.  If a keyring is not
 263  * supplied, an empty one is invented.
 264  */
 265 static int install_session_keyring(struct key *keyring)
 266 {
 267         struct cred *new;
 268         int ret;
 269
 270         new = prepare_creds();
 271         if (!new)
 272                 return -ENOMEM;
 273
 274         ret = install_session_keyring_to_cred(new, keyring);
 275         if (ret < 0) {
 276                 abort_creds(new);
 277                 return ret;
 278         }
 279
 280         return commit_creds(new);
 281 }
 282
 283 /*
 284  * Handle the fsuid changing.
 285  */
 286 void key_fsuid_changed(struct task_struct *tsk)
 287 {
 288         /* update the ownership of the thread keyring */
 289         BUG_ON(!tsk->cred);
 290         if (tsk->cred->thread_keyring) {
 291                 down_write(&tsk->cred->thread_keyring->sem);
 292                 tsk->cred->thread_keyring->uid = tsk->cred->fsuid;
 293                 up_write(&tsk->cred->thread_keyring->sem);
 294         }
 295 }
 296
 297 /*
 298  * Handle the fsgid changing.
 299  */
 300 void key_fsgid_changed(struct task_struct *tsk)
 301 {
 302         /* update the ownership of the thread keyring */
 303         BUG_ON(!tsk->cred);
 304         if (tsk->cred->thread_keyring) {
 305                 down_write(&tsk->cred->thread_keyring->sem);
 306                 tsk->cred->thread_keyring->gid = tsk->cred->fsgid;
 307                 up_write(&tsk->cred->thread_keyring->sem);
 308         }
 309 }
 310
 311 /*
 312  * Search the process keyrings attached to the supplied cred for the first
 313  * matching key.
 314  *
 315  * The search criteria are the type and the match function.  The description is
 316  * given to the match function as a parameter, but doesn't otherwise influence
 317  * the search.  Typically the match function will compare the description
 318  * parameter to the key's description.
 319  *
 320  * This can only search keyrings that grant Search permission to the supplied
 321  * credentials.  Keyrings linked to searched keyrings will also be searched if
 322  * they grant Search permission too.  Keys can only be found if they grant
 323  * Search permission to the credentials.
 324  *
 325  * Returns a pointer to the key with the key usage count incremented if
 326  * successful, -EAGAIN if we didn't find any matching key or -ENOKEY if we only
 327  * matched negative keys.
 328  *
 329  * In the case of a successful return, the possession attribute is set on the
 330  * returned key reference.
 331  */
 332 key_ref_t search_my_process_keyrings(struct key_type *type,
 333                                      const void *description,
 334                                      key_match_func_t match,
 335                                      bool no_state_check,
 336                                      const struct cred *cred)
 337 {
 338         key_ref_t key_ref, ret, err;
 339
 340         /* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
 341          * searchable, but we failed to find a key or we found a negative key;
 342          * otherwise we want to return a sample error (probably -EACCES) if
 343          * none of the keyrings were searchable
 344          *
 345          * in terms of priority: success > -ENOKEY > -EAGAIN > other error
 346          */
 347         key_ref = NULL;
 348         ret = NULL;
 349         err = ERR_PTR(-EAGAIN);
 350
 351         /* search the thread keyring first */
 352         if (cred->thread_keyring) {
 353                 key_ref = keyring_search_aux(
 354                         make_key_ref(cred->thread_keyring, 1),
 355                         cred, type, description, match, no_state_check);
 356                 if (!IS_ERR(key_ref))
 357                         goto found;
 358
 359                 switch (PTR_ERR(key_ref)) {
 360                 case -EAGAIN: /* no key */
 361                         if (ret)
 362                                 break;
 363                 case -ENOKEY: /* negative key */
 364                         ret = key_ref;
 365                         break;
 366                 default:
 367                         err = key_ref;
 368                         break;
 369                 }
 370         }
 371
 372         /* search the process keyring second */
 373         if (cred->tgcred->process_keyring) {
 374                 key_ref = keyring_search_aux(
 375                         make_key_ref(cred->tgcred->process_keyring, 1),
 376                         cred, type, description, match, no_state_check);
 377                 if (!IS_ERR(key_ref))
 378                         goto found;
 379
 380                 switch (PTR_ERR(key_ref)) {
 381                 case -EAGAIN: /* no key */
 382                         if (ret)
 383                                 break;
 384                 case -ENOKEY: /* negative key */
 385                         ret = key_ref;
 386                         break;
 387                 default:
 388                         err = key_ref;
 389                         break;
 390                 }
 391         }
 392
 393         /* search the session keyring */
 394         if (cred->tgcred->session_keyring) {
 395                 rcu_read_lock();
 396                 key_ref = keyring_search_aux(
 397                         make_key_ref(rcu_dereference(
 398                                              cred->tgcred->session_keyring),
 399                                      1),
 400                         cred, type, description, match, no_state_check);
 401                 rcu_read_unlock();
 402
 403                 if (!IS_ERR(key_ref))
 404                         goto found;
 405
 406                 switch (PTR_ERR(key_ref)) {
 407                 case -EAGAIN: /* no key */
 408                         if (ret)
 409                                 break;
 410                 case -ENOKEY: /* negative key */
 411                         ret = key_ref;
 412                         break;
 413                 default:
 414                         err = key_ref;
 415                         break;
 416                 }
 417         }
 418         /* or search the user-session keyring */
 419         else if (cred->user->session_keyring) {
 420                 key_ref = keyring_search_aux(
 421                         make_key_ref(cred->user->session_keyring, 1),
 422                         cred, type, description, match, no_state_check);
 423                 if (!IS_ERR(key_ref))
 424                         goto found;
 425
 426                 switch (PTR_ERR(key_ref)) {
 427                 case -EAGAIN: /* no key */
 428                         if (ret)
 429                                 break;
 430                 case -ENOKEY: /* negative key */
 431                         ret = key_ref;
 432                         break;
 433                 default:
 434                         err = key_ref;
 435                         break;
 436                 }
 437         }
 438
 439         /* no key - decide on the error we're going to go for */
 440         key_ref = ret ? ret : err;
 441
 442 found:
 443         return key_ref;
 444 }
 445
 446 /*
 447  * Search the process keyrings attached to the supplied cred for the first
 448  * matching key in the manner of search_my_process_keyrings(), but also search
 449  * the keys attached to the assumed authorisation key using its credentials if
 450  * one is available.
 451  *
 452  * Return same as search_my_process_keyrings().
 453  */
 454 key_ref_t search_process_keyrings(struct key_type *type,
 455                                   const void *description,
 456                                   key_match_func_t match,
 457                                   const struct cred *cred)
 458 {
 459         struct request_key_auth *rka;
 460         key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;
 461
 462         might_sleep();
 463
 464         key_ref = search_my_process_keyrings(type, description, match,
 465                                              false, cred);
 466         if (!IS_ERR(key_ref))
 467                 goto found;
 468         err = key_ref;
 469
 470         /* if this process has an instantiation authorisation key, then we also
 471          * search the keyrings of the process mentioned there
 472          * - we don't permit access to request_key auth keys via this method
 473          */
 474         if (cred->request_key_auth &&
 475             cred == current_cred() &&
 476             type != &key_type_request_key_auth
 477             ) {
 478                 /* defend against the auth key being revoked */
 479                 down_read(&cred->request_key_auth->sem);
 480
 481                 if (key_validate(cred->request_key_auth) == 0) {
 482                         rka = cred->request_key_auth->payload.data;
 483
 484                         key_ref = search_process_keyrings(type, description,
 485                                                           match, rka->cred);
 486
 487                         up_read(&cred->request_key_auth->sem);
 488
 489                         if (!IS_ERR(key_ref))
 490                                 goto found;
 491
 492                         ret = key_ref;
 493                 } else {
 494                         up_read(&cred->request_key_auth->sem);
 495                 }
 496         }
 497
 498         /* no key - decide on the error we're going to go for */
 499         if (err == ERR_PTR(-ENOKEY) || ret == ERR_PTR(-ENOKEY))
 500                 key_ref = ERR_PTR(-ENOKEY);
 501         else if (err == ERR_PTR(-EACCES))
 502                 key_ref = ret;
 503         else
 504                 key_ref = err;
 505
 506 found:
 507         return key_ref;
 508 }
 509
 510 /*
 511  * See if the key we're looking at is the target key.
 512  */
 513 int lookup_user_key_possessed(const struct key *key, const void *target)
 514 {
 515         return key == target;
 516 }
 517
 518 /*
 519  * Look up a key ID given us by userspace with a given permissions mask to get
 520  * the key it refers to.
 521  *
 522  * Flags can be passed to request that special keyrings be created if referred
 523  * to directly, to permit partially constructed keys to be found and to skip
 524  * validity and permission checks on the found key.
 525  *
 526  * Returns a pointer to the key with an incremented usage count if successful;
 527  * -EINVAL if the key ID is invalid; -ENOKEY if the key ID does not correspond
 528  * to a key or the best found key was a negative key; -EKEYREVOKED or
 529  * -EKEYEXPIRED if the best found key was revoked or expired; -EACCES if the
 530  * found key doesn't grant the requested permit or the LSM denied access to it;
 531  * or -ENOMEM if a special keyring couldn't be created.
 532  *
 533  * In the case of a successful return, the possession attribute is set on the
 534  * returned key reference.
 535  */
 536 key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
 537                           key_perm_t perm)
 538 {
 539         struct request_key_auth *rka;
 540         const struct cred *cred;
 541         struct key *key;
 542         key_ref_t key_ref, skey_ref;
 543         int ret;
 544
 545 try_again:
 546         cred = get_current_cred();
 547         key_ref = ERR_PTR(-ENOKEY);
 548
 549         switch (id) {
 550         case KEY_SPEC_THREAD_KEYRING:
 551                 if (!cred->thread_keyring) {
 552                         if (!(lflags & KEY_LOOKUP_CREATE))
 553                                 goto error;
 554
 555                         ret = install_thread_keyring();
 556                         if (ret < 0) {
 557                                 key_ref = ERR_PTR(ret);
 558                                 goto error;
 559                         }
 560                         goto reget_creds;
 561                 }
 562
 563                 key = cred->thread_keyring;
 564                 atomic_inc(&key->usage);
 565                 key_ref = make_key_ref(key, 1);
 566                 break;
 567
 568         case KEY_SPEC_PROCESS_KEYRING:
 569                 if (!cred->tgcred->process_keyring) {
 570                         if (!(lflags & KEY_LOOKUP_CREATE))
 571                                 goto error;
 572
 573                         ret = install_process_keyring();
 574                         if (ret < 0) {
 575                                 key_ref = ERR_PTR(ret);
 576                                 goto error;
 577                         }
 578                         goto reget_creds;
 579                 }
 580
 581                 key = cred->tgcred->process_keyring;
 582                 atomic_inc(&key->usage);
 583                 key_ref = make_key_ref(key, 1);
 584                 break;
 585
 586         case KEY_SPEC_SESSION_KEYRING:
 587                 if (!cred->tgcred->session_keyring) {
 588                         /* always install a session keyring upon access if one
 589                          * doesn't exist yet */
 590                         ret = install_user_keyrings();
 591                         if (ret < 0)
 592                                 goto error;
 593                         if (lflags & KEY_LOOKUP_CREATE)
 594                                 ret = join_session_keyring(NULL);
 595                         else
 596                                 ret = install_session_keyring(
 597                                         cred->user->session_keyring);
 598
 599                         if (ret < 0)
 600                                 goto error;
 601                         goto reget_creds;
 602                 } else if (cred->tgcred->session_keyring ==
 603                            cred->user->session_keyring &&
 604                            lflags & KEY_LOOKUP_CREATE) {
 605                         ret = join_session_keyring(NULL);
 606                         if (ret < 0)
 607                                 goto error;
 608                         goto reget_creds;
 609                 }
 610
 611                 rcu_read_lock();
 612                 key = rcu_dereference(cred->tgcred->session_keyring);
 613                 atomic_inc(&key->usage);
 614                 rcu_read_unlock();
 615                 key_ref = make_key_ref(key, 1);
 616                 break;
 617
 618         case KEY_SPEC_USER_KEYRING:
 619                 if (!cred->user->uid_keyring) {
 620                         ret = install_user_keyrings();
 621                         if (ret < 0)
 622                                 goto error;
 623                 }
 624
 625                 key = cred->user->uid_keyring;
 626                 atomic_inc(&key->usage);
 627                 key_ref = make_key_ref(key, 1);
 628                 break;
 629
 630         case KEY_SPEC_USER_SESSION_KEYRING:
 631                 if (!cred->user->session_keyring) {
 632                         ret = install_user_keyrings();
 633                         if (ret < 0)
 634                                 goto error;
 635                 }
 636
 637                 key = cred->user->session_keyring;
 638                 atomic_inc(&key->usage);
 639                 key_ref = make_key_ref(key, 1);
 640                 break;
 641
 642         case KEY_SPEC_GROUP_KEYRING:
 643                 /* group keyrings are not yet supported */
 644                 key_ref = ERR_PTR(-EINVAL);
 645                 goto error;
 646
 647         case KEY_SPEC_REQKEY_AUTH_KEY:
 648                 key = cred->request_key_auth;
 649                 if (!key)
 650                         goto error;
 651
 652                 atomic_inc(&key->usage);
 653                 key_ref = make_key_ref(key, 1);
 654                 break;
 655
 656         case KEY_SPEC_REQUESTOR_KEYRING:
 657                 if (!cred->request_key_auth)
 658                         goto error;
 659
 660                 down_read(&cred->request_key_auth->sem);
 661                 if (test_bit(KEY_FLAG_REVOKED,
 662                              &cred->request_key_auth->flags)) {
 663                         key_ref = ERR_PTR(-EKEYREVOKED);
 664                         key = NULL;
 665                 } else {
 666                         rka = cred->request_key_auth->payload.data;
 667                         key = rka->dest_keyring;
 668                         atomic_inc(&key->usage);
 669                 }
 670                 up_read(&cred->request_key_auth->sem);
 671                 if (!key)
 672                         goto error;
 673                 key_ref = make_key_ref(key, 1);
 674                 break;
 675
 676         default:
 677                 key_ref = ERR_PTR(-EINVAL);
 678                 if (id < 1)
 679                         goto error;
 680
 681                 key = key_lookup(id);
 682                 if (IS_ERR(key)) {
 683                         key_ref = ERR_CAST(key);
 684                         goto error;
 685                 }
 686
 687                 key_ref = make_key_ref(key, 0);
 688
 689                 /* check to see if we possess the key */
 690                 skey_ref = search_process_keyrings(key->type, key,
 691                                                    lookup_user_key_possessed,
 692                                                    cred);
 693
 694                 if (!IS_ERR(skey_ref)) {
 695                         key_put(key);
 696                         key_ref = skey_ref;
 697                 }
 698
 699                 break;
 700         }
 701
 702         /* unlink does not use the nominated key in any way, so can skip all
 703          * the permission checks as it is only concerned with the keyring */
 704         if (lflags & KEY_LOOKUP_FOR_UNLINK) {
 705                 ret = 0;
 706                 goto error;
 707         }
 708
 709         if (!(lflags & KEY_LOOKUP_PARTIAL)) {
 710                 ret = wait_for_key_construction(key, true);
 711                 switch (ret) {
 712                 case -ERESTARTSYS:
 713                         goto invalid_key;
 714                 default:
 715                         if (perm)
 716                                 goto invalid_key;
 717                 case 0:
 718                         break;
 719                 }
 720         } else if (perm) {
 721                 ret = key_validate(key);
 722                 if (ret < 0)
 723                         goto invalid_key;
 724         }
 725
 726         ret = -EIO;
 727         if (!(lflags & KEY_LOOKUP_PARTIAL) &&
 728             !test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 729                 goto invalid_key;
 730
 731         /* check the permissions */
 732         ret = key_task_permission(key_ref, cred, perm);
 733         if (ret < 0)
 734                 goto invalid_key;
 735
 736         key->last_used_at = current_kernel_time().tv_sec;
 737
 738 error:
 739         put_cred(cred);
 740         return key_ref;
 741
 742 invalid_key:
 743         key_ref_put(key_ref);
 744         key_ref = ERR_PTR(ret);
 745         goto error;
 746
 747         /* if we attempted to install a keyring, then it may have caused new
 748          * creds to be installed */
 749 reget_creds:
 750         put_cred(cred);
 751         goto try_again;
 752 }
 753
 754 /*
 755  * Join the named keyring as the session keyring if possible else attempt to
 756  * create a new one of that name and join that.
 757  *
 758  * If the name is NULL, an empty anonymous keyring will be installed as the
 759  * session keyring.
 760  *
 761  * Named session keyrings are joined with a semaphore held to prevent the
 762  * keyrings from going away whilst the attempt is made to going them and also
 763  * to prevent a race in creating compatible session keyrings.
 764  */
 765 long join_session_keyring(const char *name)
 766 {
 767         const struct cred *old;
 768         struct cred *new;
 769         struct key *keyring;
 770         long ret, serial;
 771
 772         /* only permit this if there's a single thread in the thread group -
 773          * this avoids us having to adjust the creds on all threads and risking
 774          * ENOMEM */
 775         if (!current_is_single_threaded())
 776                 return -EMLINK;
 777
 778         new = prepare_creds();
 779         if (!new)
 780                 return -ENOMEM;
 781         old = current_cred();
 782
 783         /* if no name is provided, install an anonymous keyring */
 784         if (!name) {
 785                 ret = install_session_keyring_to_cred(new, NULL);
 786                 if (ret < 0)
 787                         goto error;
 788
 789                 serial = new->tgcred->session_keyring->serial;
 790                 ret = commit_creds(new);
 791                 if (ret == 0)
 792                         ret = serial;
 793                 goto okay;
 794         }
 795
 796         /* allow the user to join or create a named keyring */
 797         mutex_lock(&key_session_mutex);
 798
 799         /* look for an existing keyring of this name */
 800         keyring = find_keyring_by_name(name, false);
 801         if (PTR_ERR(keyring) == -ENOKEY) {
 802                 /* not found - try and create a new one */
 803                 keyring = keyring_alloc(name, old->uid, old->gid, old,
 804                                         KEY_ALLOC_IN_QUOTA, NULL);
 805                 if (IS_ERR(keyring)) {
 806                         ret = PTR_ERR(keyring);
 807                         goto error2;
 808                 }
 809         } else if (IS_ERR(keyring)) {
 810                 ret = PTR_ERR(keyring);
 811                 goto error2;
 812         }
 813
 814         /* we've got a keyring - now to install it */
 815         ret = install_session_keyring_to_cred(new, keyring);
 816         if (ret < 0)
 817                 goto error2;
 818
 819         commit_creds(new);
 820         mutex_unlock(&key_session_mutex);
 821
 822         ret = keyring->serial;
 823         key_put(keyring);
 824 okay:
 825         return ret;
 826
 827 error2:
 828         mutex_unlock(&key_session_mutex);
 829 error:
 830         abort_creds(new);
 831         return ret;
 832 }
 833
 834 /*
 835  * Replace a process's session keyring on behalf of one of its children when
 836  * the target  process is about to resume userspace execution.
 837  */
 838 void key_change_session_keyring(struct callback_head *twork)
 839 {
 840         const struct cred *old = current_cred();
 841         struct cred *new = container_of(twork, struct cred, rcu);
 842
 843         if (unlikely(current->flags & PF_EXITING)) {
 844                 put_cred(new);
 845                 return;
 846         }
 847
 848         new->  uid      = old->  uid;
 849         new-> euid      = old-> euid;
 850         new-> suid      = old-> suid;
 851         new->fsuid      = old->fsuid;
 852         new->  gid      = old->  gid;
 853         new-> egid      = old-> egid;
 854         new-> sgid      = old-> sgid;
 855         new->fsgid      = old->fsgid;
 856         new->user       = get_uid(old->user);
 857         new->user_ns    = get_user_ns(new->user_ns);
 858         new->group_info = get_group_info(old->group_info);
 859
 860         new->securebits = old->securebits;
 861         new->cap_inheritable    = old->cap_inheritable;
 862         new->cap_permitted      = old->cap_permitted;
 863         new->cap_effective      = old->cap_effective;
 864         new->cap_bset           = old->cap_bset;
 865
 866         new->jit_keyring        = old->jit_keyring;
 867         new->thread_keyring     = key_get(old->thread_keyring);
 868         new->tgcred->tgid       = old->tgcred->tgid;
 869         new->tgcred->process_keyring = key_get(old->tgcred->process_keyring);
 870
 871         security_transfer_creds(new, old);
 872
 873         commit_creds(new);
 874 }