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->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->uid, tsk->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->thread_keyring;
 168         tsk->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->signal->process_keyring) {
 193                 sprintf(buf, "_pid.%u", tsk->tgid);
 194
 195                 keyring = keyring_alloc(buf, tsk->uid, tsk->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->sighand->siglock);
 204                 if (!tsk->signal->process_keyring) {
 205                         tsk->signal->process_keyring = keyring;
 206                         keyring = NULL;
 207                 }
 208                 spin_unlock_irq(&tsk->sighand->siglock);
 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->signal->session_keyring)
 239                         flags = KEY_ALLOC_IN_QUOTA;
 240
 241                 keyring = keyring_alloc(buf, tsk->uid, tsk->gid, tsk,
 242                                         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->sighand->siglock);
 252         old = tsk->signal->session_keyring;
 253         rcu_assign_pointer(tsk->signal->session_keyring, keyring);
 254         spin_unlock_irq(&tsk->sighand->siglock);
 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 in a thread group for fork without CLONE_THREAD
 270  */
 271 int copy_thread_group_keys(struct task_struct *tsk)
 272 {
 273         key_check(current->thread_group->session_keyring);
 274         key_check(current->thread_group->process_keyring);
 275
 276         /* no process keyring yet */
 277         tsk->signal->process_keyring = NULL;
 278
 279         /* same session keyring */
 280         rcu_read_lock();
 281         tsk->signal->session_keyring =
 282                 key_get(rcu_dereference(current->signal->session_keyring));
 283         rcu_read_unlock();
 284
 285         return 0;
 286
 287 } /* end copy_thread_group_keys() */
 288
 289 /*****************************************************************************/
 290 /*
 291  * copy the keys for fork
 292  */
 293 int copy_keys(unsigned long clone_flags, struct task_struct *tsk)
 294 {
 295         key_check(tsk->thread_keyring);
 296         key_check(tsk->request_key_auth);
 297
 298         /* no thread keyring yet */
 299         tsk->thread_keyring = NULL;
 300
 301         /* copy the request_key() authorisation for this thread */
 302         key_get(tsk->request_key_auth);
 303
 304         return 0;
 305
 306 } /* end copy_keys() */
 307
 308 /*****************************************************************************/
 309 /*
 310  * dispose of thread group keys upon thread group destruction
 311  */
 312 void exit_thread_group_keys(struct signal_struct *tg)
 313 {
 314         key_put(tg->session_keyring);
 315         key_put(tg->process_keyring);
 316
 317 } /* end exit_thread_group_keys() */
 318
 319 /*****************************************************************************/
 320 /*
 321  * dispose of per-thread keys upon thread exit
 322  */
 323 void exit_keys(struct task_struct *tsk)
 324 {
 325         key_put(tsk->thread_keyring);
 326         key_put(tsk->request_key_auth);
 327
 328 } /* end exit_keys() */
 329
 330 /*****************************************************************************/
 331 /*
 332  * deal with execve()
 333  */
 334 int exec_keys(struct task_struct *tsk)
 335 {
 336         struct key *old;
 337
 338         /* newly exec'd tasks don't get a thread keyring */
 339         task_lock(tsk);
 340         old = tsk->thread_keyring;
 341         tsk->thread_keyring = NULL;
 342         task_unlock(tsk);
 343
 344         key_put(old);
 345
 346         /* discard the process keyring from a newly exec'd task */
 347         spin_lock_irq(&tsk->sighand->siglock);
 348         old = tsk->signal->process_keyring;
 349         tsk->signal->process_keyring = NULL;
 350         spin_unlock_irq(&tsk->sighand->siglock);
 351
 352         key_put(old);
 353
 354         return 0;
 355
 356 } /* end exec_keys() */
 357
 358 /*****************************************************************************/
 359 /*
 360  * deal with SUID programs
 361  * - we might want to make this invent a new session keyring
 362  */
 363 int suid_keys(struct task_struct *tsk)
 364 {
 365         return 0;
 366
 367 } /* end suid_keys() */
 368
 369 /*****************************************************************************/
 370 /*
 371  * the filesystem user ID changed
 372  */
 373 void key_fsuid_changed(struct task_struct *tsk)
 374 {
 375         /* update the ownership of the thread keyring */
 376         if (tsk->thread_keyring) {
 377                 down_write(&tsk->thread_keyring->sem);
 378                 tsk->thread_keyring->uid = tsk->fsuid;
 379                 up_write(&tsk->thread_keyring->sem);
 380         }
 381
 382 } /* end key_fsuid_changed() */
 383
 384 /*****************************************************************************/
 385 /*
 386  * the filesystem group ID changed
 387  */
 388 void key_fsgid_changed(struct task_struct *tsk)
 389 {
 390         /* update the ownership of the thread keyring */
 391         if (tsk->thread_keyring) {
 392                 down_write(&tsk->thread_keyring->sem);
 393                 tsk->thread_keyring->gid = tsk->fsgid;
 394                 up_write(&tsk->thread_keyring->sem);
 395         }
 396
 397 } /* end key_fsgid_changed() */
 398
 399 /*****************************************************************************/
 400 /*
 401  * search the process keyrings for the first matching key
 402  * - we use the supplied match function to see if the description (or other
 403  *   feature of interest) matches
 404  * - we return -EAGAIN if we didn't find any matching key
 405  * - we return -ENOKEY if we found only negative matching keys
 406  */
 407 key_ref_t search_process_keyrings(struct key_type *type,
 408                                   const void *description,
 409                                   key_match_func_t match,
 410                                   struct task_struct *context)
 411 {
 412         struct request_key_auth *rka;
 413         key_ref_t key_ref, ret, err;
 414
 415         might_sleep();
 416
 417         /* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
 418          * searchable, but we failed to find a key or we found a negative key;
 419          * otherwise we want to return a sample error (probably -EACCES) if
 420          * none of the keyrings were searchable
 421          *
 422          * in terms of priority: success > -ENOKEY > -EAGAIN > other error
 423          */
 424         key_ref = NULL;
 425         ret = NULL;
 426         err = ERR_PTR(-EAGAIN);
 427
 428         /* search the thread keyring first */
 429         if (context->thread_keyring) {
 430                 key_ref = keyring_search_aux(
 431                         make_key_ref(context->thread_keyring, 1),
 432                         context, type, description, match);
 433                 if (!IS_ERR(key_ref))
 434                         goto found;
 435
 436                 switch (PTR_ERR(key_ref)) {
 437                 case -EAGAIN: /* no key */
 438                         if (ret)
 439                                 break;
 440                 case -ENOKEY: /* negative key */
 441                         ret = key_ref;
 442                         break;
 443                 default:
 444                         err = key_ref;
 445                         break;
 446                 }
 447         }
 448
 449         /* search the process keyring second */
 450         if (context->signal->process_keyring) {
 451                 key_ref = keyring_search_aux(
 452                         make_key_ref(context->signal->process_keyring, 1),
 453                         context, type, description, match);
 454                 if (!IS_ERR(key_ref))
 455                         goto found;
 456
 457                 switch (PTR_ERR(key_ref)) {
 458                 case -EAGAIN: /* no key */
 459                         if (ret)
 460                                 break;
 461                 case -ENOKEY: /* negative key */
 462                         ret = key_ref;
 463                         break;
 464                 default:
 465                         err = key_ref;
 466                         break;
 467                 }
 468         }
 469
 470         /* search the session keyring */
 471         if (context->signal->session_keyring) {
 472                 rcu_read_lock();
 473                 key_ref = keyring_search_aux(
 474                         make_key_ref(rcu_dereference(
 475                                              context->signal->session_keyring),
 476                                      1),
 477                         context, type, description, match);
 478                 rcu_read_unlock();
 479
 480                 if (!IS_ERR(key_ref))
 481                         goto found;
 482
 483                 switch (PTR_ERR(key_ref)) {
 484                 case -EAGAIN: /* no key */
 485                         if (ret)
 486                                 break;
 487                 case -ENOKEY: /* negative key */
 488                         ret = key_ref;
 489                         break;
 490                 default:
 491                         err = key_ref;
 492                         break;
 493                 }
 494         }
 495         /* or search the user-session keyring */
 496         else if (context->user->session_keyring) {
 497                 key_ref = keyring_search_aux(
 498                         make_key_ref(context->user->session_keyring, 1),
 499                         context, type, description, match);
 500                 if (!IS_ERR(key_ref))
 501                         goto found;
 502
 503                 switch (PTR_ERR(key_ref)) {
 504                 case -EAGAIN: /* no key */
 505                         if (ret)
 506                                 break;
 507                 case -ENOKEY: /* negative key */
 508                         ret = key_ref;
 509                         break;
 510                 default:
 511                         err = key_ref;
 512                         break;
 513                 }
 514         }
 515
 516         /* if this process has an instantiation authorisation key, then we also
 517          * search the keyrings of the process mentioned there
 518          * - we don't permit access to request_key auth keys via this method
 519          */
 520         if (context->request_key_auth &&
 521             context == current &&
 522             type != &key_type_request_key_auth
 523             ) {
 524                 /* defend against the auth key being revoked */
 525                 down_read(&context->request_key_auth->sem);
 526
 527                 if (key_validate(context->request_key_auth) == 0) {
 528                         rka = context->request_key_auth->payload.data;
 529
 530                         key_ref = search_process_keyrings(type, description,
 531                                                           match, rka->context);
 532
 533                         up_read(&context->request_key_auth->sem);
 534
 535                         if (!IS_ERR(key_ref))
 536                                 goto found;
 537
 538                         switch (PTR_ERR(key_ref)) {
 539                         case -EAGAIN: /* no key */
 540                                 if (ret)
 541                                         break;
 542                         case -ENOKEY: /* negative key */
 543                                 ret = key_ref;
 544                                 break;
 545                         default:
 546                                 err = key_ref;
 547                                 break;
 548                         }
 549                 } else {
 550                         up_read(&context->request_key_auth->sem);
 551                 }
 552         }
 553
 554         /* no key - decide on the error we're going to go for */
 555         key_ref = ret ? ret : err;
 556
 557 found:
 558         return key_ref;
 559
 560 } /* end search_process_keyrings() */
 561
 562 /*****************************************************************************/
 563 /*
 564  * see if the key we're looking at is the target key
 565  */
 566 static int lookup_user_key_possessed(const struct key *key, const void *target)
 567 {
 568         return key == target;
 569
 570 } /* end lookup_user_key_possessed() */
 571
 572 /*****************************************************************************/
 573 /*
 574  * lookup a key given a key ID from userspace with a given permissions mask
 575  * - don't create special keyrings unless so requested
 576  * - partially constructed keys aren't found unless requested
 577  */
 578 key_ref_t lookup_user_key(key_serial_t id, int create, int partial,
 579                           key_perm_t perm)
 580 {
 581         struct request_key_auth *rka;
 582         struct task_struct *t = current;
 583         key_ref_t key_ref, skey_ref;
 584         struct key *key;
 585         int ret;
 586
 587         key_ref = ERR_PTR(-ENOKEY);
 588
 589         switch (id) {
 590         case KEY_SPEC_THREAD_KEYRING:
 591                 if (!t->thread_keyring) {
 592                         if (!create)
 593                                 goto error;
 594
 595                         ret = install_thread_keyring();
 596                         if (ret < 0) {
 597                                 key = ERR_PTR(ret);
 598                                 goto error;
 599                         }
 600                 }
 601
 602                 key = t->thread_keyring;
 603                 atomic_inc(&key->usage);
 604                 key_ref = make_key_ref(key, 1);
 605                 break;
 606
 607         case KEY_SPEC_PROCESS_KEYRING:
 608                 if (!t->signal->process_keyring) {
 609                         if (!create)
 610                                 goto error;
 611
 612                         ret = install_process_keyring();
 613                         if (ret < 0) {
 614                                 key = ERR_PTR(ret);
 615                                 goto error;
 616                         }
 617                 }
 618
 619                 key = t->signal->process_keyring;
 620                 atomic_inc(&key->usage);
 621                 key_ref = make_key_ref(key, 1);
 622                 break;
 623
 624         case KEY_SPEC_SESSION_KEYRING:
 625                 if (!t->signal->session_keyring) {
 626                         /* always install a session keyring upon access if one
 627                          * doesn't exist yet */
 628                         ret = install_user_keyrings();
 629                         if (ret < 0)
 630                                 goto error;
 631                         ret = install_session_keyring(t->user->session_keyring);
 632                         if (ret < 0)
 633                                 goto error;
 634                 }
 635
 636                 rcu_read_lock();
 637                 key = rcu_dereference(t->signal->session_keyring);
 638                 atomic_inc(&key->usage);
 639                 rcu_read_unlock();
 640                 key_ref = make_key_ref(key, 1);
 641                 break;
 642
 643         case KEY_SPEC_USER_KEYRING:
 644                 if (!t->user->uid_keyring) {
 645                         ret = install_user_keyrings();
 646                         if (ret < 0)
 647                                 goto error;
 648                 }
 649
 650                 key = t->user->uid_keyring;
 651                 atomic_inc(&key->usage);
 652                 key_ref = make_key_ref(key, 1);
 653                 break;
 654
 655         case KEY_SPEC_USER_SESSION_KEYRING:
 656                 if (!t->user->session_keyring) {
 657                         ret = install_user_keyrings();
 658                         if (ret < 0)
 659                                 goto error;
 660                 }
 661
 662                 key = t->user->session_keyring;
 663                 atomic_inc(&key->usage);
 664                 key_ref = make_key_ref(key, 1);
 665                 break;
 666
 667         case KEY_SPEC_GROUP_KEYRING:
 668                 /* group keyrings are not yet supported */
 669                 key = ERR_PTR(-EINVAL);
 670                 goto error;
 671
 672         case KEY_SPEC_REQKEY_AUTH_KEY:
 673                 key = t->request_key_auth;
 674                 if (!key)
 675                         goto error;
 676
 677                 atomic_inc(&key->usage);
 678                 key_ref = make_key_ref(key, 1);
 679                 break;
 680
 681         case KEY_SPEC_REQUESTOR_KEYRING:
 682                 if (!t->request_key_auth)
 683                         goto error;
 684
 685                 down_read(&t->request_key_auth->sem);
 686                 if (t->request_key_auth->flags & KEY_FLAG_REVOKED) {
 687                         key_ref = ERR_PTR(-EKEYREVOKED);
 688                         key = NULL;
 689                 } else {
 690                         rka = t->request_key_auth->payload.data;
 691                         key = rka->dest_keyring;
 692                         atomic_inc(&key->usage);
 693                 }
 694                 up_read(&t->request_key_auth->sem);
 695                 if (!key)
 696                         goto error;
 697                 key_ref = make_key_ref(key, 1);
 698                 break;
 699
 700         default:
 701                 key_ref = ERR_PTR(-EINVAL);
 702                 if (id < 1)
 703                         goto error;
 704
 705                 key = key_lookup(id);
 706                 if (IS_ERR(key)) {
 707                         key_ref = ERR_CAST(key);
 708                         goto error;
 709                 }
 710
 711                 key_ref = make_key_ref(key, 0);
 712
 713                 /* check to see if we possess the key */
 714                 skey_ref = search_process_keyrings(key->type, key,
 715                                                    lookup_user_key_possessed,
 716                                                    current);
 717
 718                 if (!IS_ERR(skey_ref)) {
 719                         key_put(key);
 720                         key_ref = skey_ref;
 721                 }
 722
 723                 break;
 724         }
 725
 726         if (!partial) {
 727                 ret = wait_for_key_construction(key, true);
 728                 switch (ret) {
 729                 case -ERESTARTSYS:
 730                         goto invalid_key;
 731                 default:
 732                         if (perm)
 733                                 goto invalid_key;
 734                 case 0:
 735                         break;
 736                 }
 737         } else if (perm) {
 738                 ret = key_validate(key);
 739                 if (ret < 0)
 740                         goto invalid_key;
 741         }
 742
 743         ret = -EIO;
 744         if (!partial && !test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 745                 goto invalid_key;
 746
 747         /* check the permissions */
 748         ret = key_task_permission(key_ref, t, perm);
 749         if (ret < 0)
 750                 goto invalid_key;
 751
 752 error:
 753         return key_ref;
 754
 755 invalid_key:
 756         key_ref_put(key_ref);
 757         key_ref = ERR_PTR(ret);
 758         goto error;
 759
 760 } /* end lookup_user_key() */
 761
 762 /*****************************************************************************/
 763 /*
 764  * join the named keyring as the session keyring if possible, or attempt to
 765  * create a new one of that name if not
 766  * - if the name is NULL, an empty anonymous keyring is installed instead
 767  * - named session keyring joining is done with a semaphore held
 768  */
 769 long join_session_keyring(const char *name)
 770 {
 771         struct task_struct *tsk = current;
 772         struct key *keyring;
 773         long ret;
 774
 775         /* if no name is provided, install an anonymous keyring */
 776         if (!name) {
 777                 ret = install_session_keyring(NULL);
 778                 if (ret < 0)
 779                         goto error;
 780
 781                 rcu_read_lock();
 782                 ret = rcu_dereference(tsk->signal->session_keyring)->serial;
 783                 rcu_read_unlock();
 784                 goto error;
 785         }
 786
 787         /* allow the user to join or create a named keyring */
 788         mutex_lock(&key_session_mutex);
 789
 790         /* look for an existing keyring of this name */
 791         keyring = find_keyring_by_name(name, false);
 792         if (PTR_ERR(keyring) == -ENOKEY) {
 793                 /* not found - try and create a new one */
 794                 keyring = keyring_alloc(name, tsk->uid, tsk->gid, tsk,
 795                                         KEY_ALLOC_IN_QUOTA, NULL);
 796                 if (IS_ERR(keyring)) {
 797                         ret = PTR_ERR(keyring);
 798                         goto error2;
 799                 }
 800         }
 801         else if (IS_ERR(keyring)) {
 802                 ret = PTR_ERR(keyring);
 803                 goto error2;
 804         }
 805
 806         /* we've got a keyring - now to install it */
 807         ret = install_session_keyring(keyring);
 808         if (ret < 0)
 809                 goto error2;
 810
 811         ret = keyring->serial;
 812         key_put(keyring);
 813
 814 error2:
 815         mutex_unlock(&key_session_mutex);
 816 error:
 817         return ret;
 818
 819 } /* end join_session_keyring() */