SAFE public projects git trees. - safe/jmp/linux-2.6/blob - security/keys/process_keys.c

   1 /* Management of 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/slab.h>
  16 #include <linux/keyctl.h>
  17 #include <linux/fs.h>
  18 #include <linux/err.h>
  19 #include <linux/mutex.h>
  20 #include <asm/uaccess.h>
  21 #include "internal.h"
  22
  23 /* session keyring create vs join semaphore */
  24 static DEFINE_MUTEX(key_session_mutex);
  25
  26 /* user keyring creation semaphore */
  27 static DEFINE_MUTEX(key_user_keyring_mutex);
  28
  29 /* the root user's tracking struct */
  30 struct key_user root_key_user = {
  31         .usage          = ATOMIC_INIT(3),
  32         .cons_lock      = __MUTEX_INITIALIZER(root_key_user.cons_lock),
  33         .lock           = __SPIN_LOCK_UNLOCKED(root_key_user.lock),
  34         .nkeys          = ATOMIC_INIT(2),
  35         .nikeys         = ATOMIC_INIT(2),
  36         .uid            = 0,
  37 };
  38
  39 /*****************************************************************************/
  40 /*
  41  * install user and user session keyrings for a particular UID
  42  */
  43 int install_user_keyrings(void)
  44 {
  45         struct user_struct *user = current->cred->user;
  46         struct key *uid_keyring, *session_keyring;
  47         char buf[20];
  48         int ret;
  49
  50         kenter("%p{%u}", user, user->uid);
  51
  52         if (user->uid_keyring) {
  53                 kleave(" = 0 [exist]");
  54                 return 0;
  55         }
  56
  57         mutex_lock(&key_user_keyring_mutex);
  58         ret = 0;
  59
  60         if (!user->uid_keyring) {
  61                 /* get the UID-specific keyring
  62                  * - there may be one in existence already as it may have been
  63                  *   pinned by a session, but the user_struct pointing to it
  64                  *   may have been destroyed by setuid */
  65                 sprintf(buf, "_uid.%u", user->uid);
  66
  67                 uid_keyring = find_keyring_by_name(buf, true);
  68                 if (IS_ERR(uid_keyring)) {
  69                         uid_keyring = keyring_alloc(buf, user->uid, (gid_t) -1,
  70                                                     current, KEY_ALLOC_IN_QUOTA,
  71                                                     NULL);
  72                         if (IS_ERR(uid_keyring)) {
  73                                 ret = PTR_ERR(uid_keyring);
  74                                 goto error;
  75                         }
  76                 }
  77
  78                 /* get a default session keyring (which might also exist
  79                  * already) */
  80                 sprintf(buf, "_uid_ses.%u", user->uid);
  81
  82                 session_keyring = find_keyring_by_name(buf, true);
  83                 if (IS_ERR(session_keyring)) {
  84                         session_keyring =
  85                                 keyring_alloc(buf, user->uid, (gid_t) -1,
  86                                               current, KEY_ALLOC_IN_QUOTA,
  87                                               NULL);
  88                         if (IS_ERR(session_keyring)) {
  89                                 ret = PTR_ERR(session_keyring);
  90                                 goto error_release;
  91                         }
  92
  93                         /* we install a link from the user session keyring to
  94                          * the user keyring */
  95                         ret = key_link(session_keyring, uid_keyring);
  96                         if (ret < 0)
  97                                 goto error_release_both;
  98                 }
  99
 100                 /* install the keyrings */
 101                 user->uid_keyring = uid_keyring;
 102                 user->session_keyring = session_keyring;
 103         }
 104
 105         mutex_unlock(&key_user_keyring_mutex);
 106         kleave(" = 0");
 107         return 0;
 108
 109 error_release_both:
 110         key_put(session_keyring);
 111 error_release:
 112         key_put(uid_keyring);
 113 error:
 114         mutex_unlock(&key_user_keyring_mutex);
 115         kleave(" = %d", ret);
 116         return ret;
 117 }
 118
 119 /*****************************************************************************/
 120 /*
 121  * deal with the UID changing
 122  */
 123 void switch_uid_keyring(struct user_struct *new_user)
 124 {
 125 #if 0 /* do nothing for now */
 126         struct key *old;
 127
 128         /* switch to the new user's session keyring if we were running under
 129          * root's default session keyring */
 130         if (new_user->uid != 0 &&
 131             current->session_keyring == &root_session_keyring
 132             ) {
 133                 atomic_inc(&new_user->session_keyring->usage);
 134
 135                 task_lock(current);
 136                 old = current->session_keyring;
 137                 current->session_keyring = new_user->session_keyring;
 138                 task_unlock(current);
 139
 140                 key_put(old);
 141         }
 142 #endif
 143
 144 } /* end switch_uid_keyring() */
 145
 146 /*****************************************************************************/
 147 /*
 148  * install a fresh thread keyring, discarding the old one
 149  */
 150 int install_thread_keyring(void)
 151 {
 152         struct task_struct *tsk = current;
 153         struct key *keyring, *old;
 154         char buf[20];
 155         int ret;
 156
 157         sprintf(buf, "_tid.%u", tsk->pid);
 158
 159         keyring = keyring_alloc(buf, tsk->cred->uid, tsk->cred->gid, tsk,
 160                                 KEY_ALLOC_QUOTA_OVERRUN, NULL);
 161         if (IS_ERR(keyring)) {
 162                 ret = PTR_ERR(keyring);
 163                 goto error;
 164         }
 165
 166         task_lock(tsk);
 167         old = tsk->cred->thread_keyring;
 168         tsk->cred->thread_keyring = keyring;
 169         task_unlock(tsk);
 170
 171         ret = 0;
 172
 173         key_put(old);
 174 error:
 175         return ret;
 176
 177 } /* end install_thread_keyring() */
 178
 179 /*****************************************************************************/
 180 /*
 181  * make sure a process keyring is installed
 182  */
 183 int install_process_keyring(void)
 184 {
 185         struct task_struct *tsk = current;
 186         struct key *keyring;
 187         char buf[20];
 188         int ret;
 189
 190         might_sleep();
 191
 192         if (!tsk->cred->tgcred->process_keyring) {
 193                 sprintf(buf, "_pid.%u", tsk->tgid);
 194
 195                 keyring = keyring_alloc(buf, tsk->cred->uid, tsk->cred->gid, tsk,
 196                                         KEY_ALLOC_QUOTA_OVERRUN, NULL);
 197                 if (IS_ERR(keyring)) {
 198                         ret = PTR_ERR(keyring);
 199                         goto error;
 200                 }
 201
 202                 /* attach keyring */
 203                 spin_lock_irq(&tsk->cred->tgcred->lock);
 204                 if (!tsk->cred->tgcred->process_keyring) {
 205                         tsk->cred->tgcred->process_keyring = keyring;
 206                         keyring = NULL;
 207                 }
 208                 spin_unlock_irq(&tsk->cred->tgcred->lock);
 209
 210                 key_put(keyring);
 211         }
 212
 213         ret = 0;
 214 error:
 215         return ret;
 216
 217 } /* end install_process_keyring() */
 218
 219 /*****************************************************************************/
 220 /*
 221  * install a session keyring, discarding the old one
 222  * - if a keyring is not supplied, an empty one is invented
 223  */
 224 static int install_session_keyring(struct key *keyring)
 225 {
 226         struct task_struct *tsk = current;
 227         unsigned long flags;
 228         struct key *old;
 229         char buf[20];
 230
 231         might_sleep();
 232
 233         /* create an empty session keyring */
 234         if (!keyring) {
 235                 sprintf(buf, "_ses.%u", tsk->tgid);
 236
 237                 flags = KEY_ALLOC_QUOTA_OVERRUN;
 238                 if (tsk->cred->tgcred->session_keyring)
 239                         flags = KEY_ALLOC_IN_QUOTA;
 240
 241                 keyring = keyring_alloc(buf, tsk->cred->uid, tsk->cred->gid,
 242                                         tsk, flags, NULL);
 243                 if (IS_ERR(keyring))
 244                         return PTR_ERR(keyring);
 245         }
 246         else {
 247                 atomic_inc(&keyring->usage);
 248         }
 249
 250         /* install the keyring */
 251         spin_lock_irq(&tsk->cred->tgcred->lock);
 252         old = tsk->cred->tgcred->session_keyring;
 253         rcu_assign_pointer(tsk->cred->tgcred->session_keyring, keyring);
 254         spin_unlock_irq(&tsk->cred->tgcred->lock);
 255
 256         /* we're using RCU on the pointer, but there's no point synchronising
 257          * on it if it didn't previously point to anything */
 258         if (old) {
 259                 synchronize_rcu();
 260                 key_put(old);
 261         }
 262
 263         return 0;
 264
 265 } /* end install_session_keyring() */
 266
 267 /*****************************************************************************/
 268 /*
 269  * copy the keys for fork
 270  */
 271 int copy_keys(unsigned long clone_flags, struct task_struct *tsk)
 272 {
 273         key_check(tsk->cred->thread_keyring);
 274         key_check(tsk->cred->request_key_auth);
 275
 276         /* no thread keyring yet */
 277         tsk->cred->thread_keyring = NULL;
 278
 279         /* copy the request_key() authorisation for this thread */
 280         key_get(tsk->cred->request_key_auth);
 281
 282         return 0;
 283
 284 } /* end copy_keys() */
 285
 286 /*****************************************************************************/
 287 /*
 288  * dispose of per-thread keys upon thread exit
 289  */
 290 void exit_keys(struct task_struct *tsk)
 291 {
 292         key_put(tsk->cred->thread_keyring);
 293         key_put(tsk->cred->request_key_auth);
 294
 295 } /* end exit_keys() */
 296
 297 /*****************************************************************************/
 298 /*
 299  * deal with execve()
 300  */
 301 int exec_keys(struct task_struct *tsk)
 302 {
 303         struct key *old;
 304
 305         /* newly exec'd tasks don't get a thread keyring */
 306         task_lock(tsk);
 307         old = tsk->cred->thread_keyring;
 308         tsk->cred->thread_keyring = NULL;
 309         task_unlock(tsk);
 310
 311         key_put(old);
 312
 313         /* discard the process keyring from a newly exec'd task */
 314         spin_lock_irq(&tsk->cred->tgcred->lock);
 315         old = tsk->cred->tgcred->process_keyring;
 316         tsk->cred->tgcred->process_keyring = NULL;
 317         spin_unlock_irq(&tsk->cred->tgcred->lock);
 318
 319         key_put(old);
 320
 321         return 0;
 322
 323 } /* end exec_keys() */
 324
 325 /*****************************************************************************/
 326 /*
 327  * deal with SUID programs
 328  * - we might want to make this invent a new session keyring
 329  */
 330 int suid_keys(struct task_struct *tsk)
 331 {
 332         return 0;
 333
 334 } /* end suid_keys() */
 335
 336 /*****************************************************************************/
 337 /*
 338  * the filesystem user ID changed
 339  */
 340 void key_fsuid_changed(struct task_struct *tsk)
 341 {
 342         /* update the ownership of the thread keyring */
 343         BUG_ON(!tsk->cred);
 344         if (tsk->cred->thread_keyring) {
 345                 down_write(&tsk->cred->thread_keyring->sem);
 346                 tsk->cred->thread_keyring->uid = tsk->cred->fsuid;
 347                 up_write(&tsk->cred->thread_keyring->sem);
 348         }
 349
 350 } /* end key_fsuid_changed() */
 351
 352 /*****************************************************************************/
 353 /*
 354  * the filesystem group ID changed
 355  */
 356 void key_fsgid_changed(struct task_struct *tsk)
 357 {
 358         /* update the ownership of the thread keyring */
 359         BUG_ON(!tsk->cred);
 360         if (tsk->cred->thread_keyring) {
 361                 down_write(&tsk->cred->thread_keyring->sem);
 362                 tsk->cred->thread_keyring->gid = tsk->cred->fsgid;
 363                 up_write(&tsk->cred->thread_keyring->sem);
 364         }
 365
 366 } /* end key_fsgid_changed() */
 367
 368 /*****************************************************************************/
 369 /*
 370  * search the process keyrings for the first matching key
 371  * - we use the supplied match function to see if the description (or other
 372  *   feature of interest) matches
 373  * - we return -EAGAIN if we didn't find any matching key
 374  * - we return -ENOKEY if we found only negative matching keys
 375  */
 376 key_ref_t search_process_keyrings(struct key_type *type,
 377                                   const void *description,
 378                                   key_match_func_t match,
 379                                   struct task_struct *context)
 380 {
 381         struct request_key_auth *rka;
 382         struct cred *cred;
 383         key_ref_t key_ref, ret, err;
 384
 385         might_sleep();
 386
 387         cred = get_task_cred(context);
 388
 389         /* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
 390          * searchable, but we failed to find a key or we found a negative key;
 391          * otherwise we want to return a sample error (probably -EACCES) if
 392          * none of the keyrings were searchable
 393          *
 394          * in terms of priority: success > -ENOKEY > -EAGAIN > other error
 395          */
 396         key_ref = NULL;
 397         ret = NULL;
 398         err = ERR_PTR(-EAGAIN);
 399
 400         /* search the thread keyring first */
 401         if (cred->thread_keyring) {
 402                 key_ref = keyring_search_aux(
 403                         make_key_ref(cred->thread_keyring, 1),
 404                         context, type, description, match);
 405                 if (!IS_ERR(key_ref))
 406                         goto found;
 407
 408                 switch (PTR_ERR(key_ref)) {
 409                 case -EAGAIN: /* no key */
 410                         if (ret)
 411                                 break;
 412                 case -ENOKEY: /* negative key */
 413                         ret = key_ref;
 414                         break;
 415                 default:
 416                         err = key_ref;
 417                         break;
 418                 }
 419         }
 420
 421         /* search the process keyring second */
 422         if (cred->tgcred->process_keyring) {
 423                 key_ref = keyring_search_aux(
 424                         make_key_ref(cred->tgcred->process_keyring, 1),
 425                         context, type, description, match);
 426                 if (!IS_ERR(key_ref))
 427                         goto found;
 428
 429                 switch (PTR_ERR(key_ref)) {
 430                 case -EAGAIN: /* no key */
 431                         if (ret)
 432                                 break;
 433                 case -ENOKEY: /* negative key */
 434                         ret = key_ref;
 435                         break;
 436                 default:
 437                         err = key_ref;
 438                         break;
 439                 }
 440         }
 441
 442         /* search the session keyring */
 443         if (cred->tgcred->session_keyring) {
 444                 rcu_read_lock();
 445                 key_ref = keyring_search_aux(
 446                         make_key_ref(rcu_dereference(
 447                                              cred->tgcred->session_keyring),
 448                                      1),
 449                         context, type, description, match);
 450                 rcu_read_unlock();
 451
 452                 if (!IS_ERR(key_ref))
 453                         goto found;
 454
 455                 switch (PTR_ERR(key_ref)) {
 456                 case -EAGAIN: /* no key */
 457                         if (ret)
 458                                 break;
 459                 case -ENOKEY: /* negative key */
 460                         ret = key_ref;
 461                         break;
 462                 default:
 463                         err = key_ref;
 464                         break;
 465                 }
 466         }
 467         /* or search the user-session keyring */
 468         else if (cred->user->session_keyring) {
 469                 key_ref = keyring_search_aux(
 470                         make_key_ref(cred->user->session_keyring, 1),
 471                         context, type, description, match);
 472                 if (!IS_ERR(key_ref))
 473                         goto found;
 474
 475                 switch (PTR_ERR(key_ref)) {
 476                 case -EAGAIN: /* no key */
 477                         if (ret)
 478                                 break;
 479                 case -ENOKEY: /* negative key */
 480                         ret = key_ref;
 481                         break;
 482                 default:
 483                         err = key_ref;
 484                         break;
 485                 }
 486         }
 487
 488         /* if this process has an instantiation authorisation key, then we also
 489          * search the keyrings of the process mentioned there
 490          * - we don't permit access to request_key auth keys via this method
 491          */
 492         if (cred->request_key_auth &&
 493             context == current &&
 494             type != &key_type_request_key_auth
 495             ) {
 496                 /* defend against the auth key being revoked */
 497                 down_read(&cred->request_key_auth->sem);
 498
 499                 if (key_validate(cred->request_key_auth) == 0) {
 500                         rka = cred->request_key_auth->payload.data;
 501
 502                         key_ref = search_process_keyrings(type, description,
 503                                                           match, rka->context);
 504
 505                         up_read(&cred->request_key_auth->sem);
 506
 507                         if (!IS_ERR(key_ref))
 508                                 goto found;
 509
 510                         switch (PTR_ERR(key_ref)) {
 511                         case -EAGAIN: /* no key */
 512                                 if (ret)
 513                                         break;
 514                         case -ENOKEY: /* negative key */
 515                                 ret = key_ref;
 516                                 break;
 517                         default:
 518                                 err = key_ref;
 519                                 break;
 520                         }
 521                 } else {
 522                         up_read(&cred->request_key_auth->sem);
 523                 }
 524         }
 525
 526         /* no key - decide on the error we're going to go for */
 527         key_ref = ret ? ret : err;
 528
 529 found:
 530         put_cred(cred);
 531         return key_ref;
 532
 533 } /* end search_process_keyrings() */
 534
 535 /*****************************************************************************/
 536 /*
 537  * see if the key we're looking at is the target key
 538  */
 539 static int lookup_user_key_possessed(const struct key *key, const void *target)
 540 {
 541         return key == target;
 542
 543 } /* end lookup_user_key_possessed() */
 544
 545 /*****************************************************************************/
 546 /*
 547  * lookup a key given a key ID from userspace with a given permissions mask
 548  * - don't create special keyrings unless so requested
 549  * - partially constructed keys aren't found unless requested
 550  */
 551 key_ref_t lookup_user_key(key_serial_t id, int create, int partial,
 552                           key_perm_t perm)
 553 {
 554         struct request_key_auth *rka;
 555         struct task_struct *t = current;
 556         struct cred *cred;
 557         struct key *key;
 558         key_ref_t key_ref, skey_ref;
 559         int ret;
 560
 561 try_again:
 562         cred = get_current_cred();
 563         key_ref = ERR_PTR(-ENOKEY);
 564
 565         switch (id) {
 566         case KEY_SPEC_THREAD_KEYRING:
 567                 if (!cred->thread_keyring) {
 568                         if (!create)
 569                                 goto error;
 570
 571                         ret = install_thread_keyring();
 572                         if (ret < 0) {
 573                                 key = ERR_PTR(ret);
 574                                 goto error;
 575                         }
 576                         goto reget_creds;
 577                 }
 578
 579                 key = cred->thread_keyring;
 580                 atomic_inc(&key->usage);
 581                 key_ref = make_key_ref(key, 1);
 582                 break;
 583
 584         case KEY_SPEC_PROCESS_KEYRING:
 585                 if (!cred->tgcred->process_keyring) {
 586                         if (!create)
 587                                 goto error;
 588
 589                         ret = install_process_keyring();
 590                         if (ret < 0) {
 591                                 key = ERR_PTR(ret);
 592                                 goto error;
 593                         }
 594                         goto reget_creds;
 595                 }
 596
 597                 key = cred->tgcred->process_keyring;
 598                 atomic_inc(&key->usage);
 599                 key_ref = make_key_ref(key, 1);
 600                 break;
 601
 602         case KEY_SPEC_SESSION_KEYRING:
 603                 if (!cred->tgcred->session_keyring) {
 604                         /* always install a session keyring upon access if one
 605                          * doesn't exist yet */
 606                         ret = install_user_keyrings();
 607                         if (ret < 0)
 608                                 goto error;
 609                         ret = install_session_keyring(
 610                                 cred->user->session_keyring);
 611                         if (ret < 0)
 612                                 goto error;
 613                         goto reget_creds;
 614                 }
 615
 616                 rcu_read_lock();
 617                 key = rcu_dereference(cred->tgcred->session_keyring);
 618                 atomic_inc(&key->usage);
 619                 rcu_read_unlock();
 620                 key_ref = make_key_ref(key, 1);
 621                 break;
 622
 623         case KEY_SPEC_USER_KEYRING:
 624                 if (!cred->user->uid_keyring) {
 625                         ret = install_user_keyrings();
 626                         if (ret < 0)
 627                                 goto error;
 628                 }
 629
 630                 key = cred->user->uid_keyring;
 631                 atomic_inc(&key->usage);
 632                 key_ref = make_key_ref(key, 1);
 633                 break;
 634
 635         case KEY_SPEC_USER_SESSION_KEYRING:
 636                 if (!cred->user->session_keyring) {
 637                         ret = install_user_keyrings();
 638                         if (ret < 0)
 639                                 goto error;
 640                 }
 641
 642                 key = cred->user->session_keyring;
 643                 atomic_inc(&key->usage);
 644                 key_ref = make_key_ref(key, 1);
 645                 break;
 646
 647         case KEY_SPEC_GROUP_KEYRING:
 648                 /* group keyrings are not yet supported */
 649                 key = ERR_PTR(-EINVAL);
 650                 goto error;
 651
 652         case KEY_SPEC_REQKEY_AUTH_KEY:
 653                 key = cred->request_key_auth;
 654                 if (!key)
 655                         goto error;
 656
 657                 atomic_inc(&key->usage);
 658                 key_ref = make_key_ref(key, 1);
 659                 break;
 660
 661         case KEY_SPEC_REQUESTOR_KEYRING:
 662                 if (!cred->request_key_auth)
 663                         goto error;
 664
 665                 down_read(&cred->request_key_auth->sem);
 666                 if (cred->request_key_auth->flags & KEY_FLAG_REVOKED) {
 667                         key_ref = ERR_PTR(-EKEYREVOKED);
 668                         key = NULL;
 669                 } else {
 670                         rka = cred->request_key_auth->payload.data;
 671                         key = rka->dest_keyring;
 672                         atomic_inc(&key->usage);
 673                 }
 674                 up_read(&cred->request_key_auth->sem);
 675                 if (!key)
 676                         goto error;
 677                 key_ref = make_key_ref(key, 1);
 678                 break;
 679
 680         default:
 681                 key_ref = ERR_PTR(-EINVAL);
 682                 if (id < 1)
 683                         goto error;
 684
 685                 key = key_lookup(id);
 686                 if (IS_ERR(key)) {
 687                         key_ref = ERR_CAST(key);
 688                         goto error;
 689                 }
 690
 691                 key_ref = make_key_ref(key, 0);
 692
 693                 /* check to see if we possess the key */
 694                 skey_ref = search_process_keyrings(key->type, key,
 695                                                    lookup_user_key_possessed,
 696                                                    current);
 697
 698                 if (!IS_ERR(skey_ref)) {
 699                         key_put(key);
 700                         key_ref = skey_ref;
 701                 }
 702
 703                 break;
 704         }
 705
 706         if (!partial) {
 707                 ret = wait_for_key_construction(key, true);
 708                 switch (ret) {
 709                 case -ERESTARTSYS:
 710                         goto invalid_key;
 711                 default:
 712                         if (perm)
 713                                 goto invalid_key;
 714                 case 0:
 715                         break;
 716                 }
 717         } else if (perm) {
 718                 ret = key_validate(key);
 719                 if (ret < 0)
 720                         goto invalid_key;
 721         }
 722
 723         ret = -EIO;
 724         if (!partial && !test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 725                 goto invalid_key;
 726
 727         /* check the permissions */
 728         ret = key_task_permission(key_ref, t, perm);
 729         if (ret < 0)
 730                 goto invalid_key;
 731
 732 error:
 733         put_cred(cred);
 734         return key_ref;
 735
 736 invalid_key:
 737         key_ref_put(key_ref);
 738         key_ref = ERR_PTR(ret);
 739         goto error;
 740
 741         /* if we attempted to install a keyring, then it may have caused new
 742          * creds to be installed */
 743 reget_creds:
 744         put_cred(cred);
 745         goto try_again;
 746
 747 } /* end lookup_user_key() */
 748
 749 /*****************************************************************************/
 750 /*
 751  * join the named keyring as the session keyring if possible, or attempt to
 752  * create a new one of that name if not
 753  * - if the name is NULL, an empty anonymous keyring is installed instead
 754  * - named session keyring joining is done with a semaphore held
 755  */
 756 long join_session_keyring(const char *name)
 757 {
 758         struct task_struct *tsk = current;
 759         struct cred *cred = current->cred;
 760         struct key *keyring;
 761         long ret;
 762
 763         /* if no name is provided, install an anonymous keyring */
 764         if (!name) {
 765                 ret = install_session_keyring(NULL);
 766                 if (ret < 0)
 767                         goto error;
 768
 769                 rcu_read_lock();
 770                 ret = rcu_dereference(cred->tgcred->session_keyring)->serial;
 771                 rcu_read_unlock();
 772                 goto error;
 773         }
 774
 775         /* allow the user to join or create a named keyring */
 776         mutex_lock(&key_session_mutex);
 777
 778         /* look for an existing keyring of this name */
 779         keyring = find_keyring_by_name(name, false);
 780         if (PTR_ERR(keyring) == -ENOKEY) {
 781                 /* not found - try and create a new one */
 782                 keyring = keyring_alloc(name, cred->uid, cred->gid, tsk,
 783                                         KEY_ALLOC_IN_QUOTA, NULL);
 784                 if (IS_ERR(keyring)) {
 785                         ret = PTR_ERR(keyring);
 786                         goto error2;
 787                 }
 788         }
 789         else if (IS_ERR(keyring)) {
 790                 ret = PTR_ERR(keyring);
 791                 goto error2;
 792         }
 793
 794         /* we've got a keyring - now to install it */
 795         ret = install_session_keyring(keyring);
 796         if (ret < 0)
 797                 goto error2;
 798
 799         ret = keyring->serial;
 800         key_put(keyring);
 801
 802 error2:
 803         mutex_unlock(&key_session_mutex);
 804 error:
 805         return ret;
 806
 807 } /* end join_session_keyring() */