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