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 && user->session_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 thread keyring to the given credentials struct if it didn't have
 125  * one already.  This is allowed to overrun the quota.
 126  *
 127  * Return: 0 if a thread keyring is now present; -errno on failure.
 128  */
 129 int install_thread_keyring_to_cred(struct cred *new)
 130 {
 131         struct key *keyring;
 132
 133         if (new->thread_keyring)
 134                 return 0;
 135
 136         keyring = keyring_alloc("_tid", new->uid, new->gid, new,
 137                                 KEY_ALLOC_QUOTA_OVERRUN, NULL);
 138         if (IS_ERR(keyring))
 139                 return PTR_ERR(keyring);
 140
 141         new->thread_keyring = keyring;
 142         return 0;
 143 }
 144
 145 /*
 146  * Install a thread keyring to the current task if it didn't have one already.
 147  *
 148  * Return: 0 if a thread keyring is now present; -errno on failure.
 149  */
 150 static int install_thread_keyring(void)
 151 {
 152         struct cred *new;
 153         int ret;
 154
 155         new = prepare_creds();
 156         if (!new)
 157                 return -ENOMEM;
 158
 159         ret = install_thread_keyring_to_cred(new);
 160         if (ret < 0) {
 161                 abort_creds(new);
 162                 return ret;
 163         }
 164
 165         return commit_creds(new);
 166 }
 167
 168 /*
 169  * Install a process keyring to the given credentials struct if it didn't have
 170  * one already.  This is allowed to overrun the quota.
 171  *
 172  * Return: 0 if a process keyring is now present; -errno on failure.
 173  */
 174 int install_process_keyring_to_cred(struct cred *new)
 175 {
 176         struct key *keyring;
 177         int ret;
 178
 179         if (new->tgcred->process_keyring)
 180                 return 0;
 181
 182         keyring = keyring_alloc("_pid", new->uid, new->gid,
 183                                 new, KEY_ALLOC_QUOTA_OVERRUN, NULL);
 184         if (IS_ERR(keyring))
 185                 return PTR_ERR(keyring);
 186
 187         spin_lock_irq(&new->tgcred->lock);
 188         if (!new->tgcred->process_keyring) {
 189                 new->tgcred->process_keyring = keyring;
 190                 keyring = NULL;
 191                 ret = 0;
 192         } else {
 193                 ret = -EEXIST;
 194         }
 195         spin_unlock_irq(&new->tgcred->lock);
 196         key_put(keyring);
 197         return ret;
 198 }
 199
 200 /*
 201  * Install a process keyring to the current task if it didn't have one already.
 202  *
 203  * Return: 0 if a process keyring is now present; -errno on failure.
 204  */
 205 static int install_process_keyring(void)
 206 {
 207         struct cred *new;
 208         int ret;
 209
 210         new = prepare_creds();
 211         if (!new)
 212                 return -ENOMEM;
 213
 214         ret = install_process_keyring_to_cred(new);
 215         if (ret < 0) {
 216                 abort_creds(new);
 217                 return ret;
 218         }
 219
 220         return commit_creds(new);
 221 }
 222
 223 /*
 224  * Install the given keyring as the session keyring of the given credentials
 225  * struct, replacing the existing one if any.  If the given keyring is NULL,
 226  * then install a new anonymous session keyring.
 227  *
 228  * Return: 0 on success; -errno on failure.
 229  */
 230 int install_session_keyring_to_cred(struct cred *cred, struct key *keyring)
 231 {
 232         unsigned long flags;
 233         struct key *old;
 234
 235         might_sleep();
 236
 237         /* create an empty session keyring */
 238         if (!keyring) {
 239                 flags = KEY_ALLOC_QUOTA_OVERRUN;
 240                 if (cred->tgcred->session_keyring)
 241                         flags = KEY_ALLOC_IN_QUOTA;
 242
 243                 keyring = keyring_alloc("_ses", cred->uid, cred->gid,
 244                                         cred, flags, NULL);
 245                 if (IS_ERR(keyring))
 246                         return PTR_ERR(keyring);
 247         } else {
 248                 atomic_inc(&keyring->usage);
 249         }
 250
 251         /* install the keyring */
 252         spin_lock_irq(&cred->tgcred->lock);
 253         old = cred->tgcred->session_keyring;
 254         rcu_assign_pointer(cred->tgcred->session_keyring, keyring);
 255         spin_unlock_irq(&cred->tgcred->lock);
 256
 257         /* we're using RCU on the pointer, but there's no point synchronising
 258          * on it if it didn't previously point to anything */
 259         if (old) {
 260                 synchronize_rcu();
 261                 key_put(old);
 262         }
 263
 264         return 0;
 265 }
 266
 267 /*
 268  * Install the given keyring as the session keyring of the current task,
 269  * replacing the existing one if any.  If the given keyring is NULL, then
 270  * install a new anonymous session keyring.
 271  *
 272  * Return: 0 on success; -errno on failure.
 273  */
 274 static int install_session_keyring(struct key *keyring)
 275 {
 276         struct cred *new;
 277         int ret;
 278
 279         new = prepare_creds();
 280         if (!new)
 281                 return -ENOMEM;
 282
 283         ret = install_session_keyring_to_cred(new, keyring);
 284         if (ret < 0) {
 285                 abort_creds(new);
 286                 return ret;
 287         }
 288
 289         return commit_creds(new);
 290 }
 291
 292 /*
 293  * Handle the fsuid changing.
 294  */
 295 void key_fsuid_changed(struct task_struct *tsk)
 296 {
 297         /* update the ownership of the thread keyring */
 298         BUG_ON(!tsk->cred);
 299         if (tsk->cred->thread_keyring) {
 300                 down_write(&tsk->cred->thread_keyring->sem);
 301                 tsk->cred->thread_keyring->uid = tsk->cred->fsuid;
 302                 up_write(&tsk->cred->thread_keyring->sem);
 303         }
 304 }
 305
 306 /*
 307  * Handle the fsgid changing.
 308  */
 309 void key_fsgid_changed(struct task_struct *tsk)
 310 {
 311         /* update the ownership of the thread keyring */
 312         BUG_ON(!tsk->cred);
 313         if (tsk->cred->thread_keyring) {
 314                 down_write(&tsk->cred->thread_keyring->sem);
 315                 tsk->cred->thread_keyring->gid = tsk->cred->fsgid;
 316                 up_write(&tsk->cred->thread_keyring->sem);
 317         }
 318 }
 319
 320 /*
 321  * Search the process keyrings attached to the supplied cred for the first
 322  * matching key.
 323  *
 324  * The search criteria are the type and the match function.  The description is
 325  * given to the match function as a parameter, but doesn't otherwise influence
 326  * the search.  Typically the match function will compare the description
 327  * parameter to the key's description.
 328  *
 329  * This can only search keyrings that grant Search permission to the supplied
 330  * credentials.  Keyrings linked to searched keyrings will also be searched if
 331  * they grant Search permission too.  Keys can only be found if they grant
 332  * Search permission to the credentials.
 333  *
 334  * Returns a pointer to the key with the key usage count incremented if
 335  * successful, -EAGAIN if we didn't find any matching key or -ENOKEY if we only
 336  * matched negative keys.
 337  *
 338  * In the case of a successful return, the possession attribute is set on the
 339  * returned key reference.
 340  */
 341 key_ref_t search_my_process_keyrings(struct key_type *type,
 342                                      const void *description,
 343                                      key_match_func_t match,
 344                                      bool no_state_check,
 345                                      const struct cred *cred)
 346 {
 347         key_ref_t key_ref, ret, err;
 348
 349         /* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
 350          * searchable, but we failed to find a key or we found a negative key;
 351          * otherwise we want to return a sample error (probably -EACCES) if
 352          * none of the keyrings were searchable
 353          *
 354          * in terms of priority: success > -ENOKEY > -EAGAIN > other error
 355          */
 356         key_ref = NULL;
 357         ret = NULL;
 358         err = ERR_PTR(-EAGAIN);
 359
 360         /* search the thread keyring first */
 361         if (cred->thread_keyring) {
 362                 key_ref = keyring_search_aux(
 363                         make_key_ref(cred->thread_keyring, 1),
 364                         cred, type, description, match, no_state_check);
 365                 if (!IS_ERR(key_ref))
 366                         goto found;
 367
 368                 switch (PTR_ERR(key_ref)) {
 369                 case -EAGAIN: /* no key */
 370                         if (ret)
 371                                 break;
 372                 case -ENOKEY: /* negative key */
 373                         ret = key_ref;
 374                         break;
 375                 default:
 376                         err = key_ref;
 377                         break;
 378                 }
 379         }
 380
 381         /* search the process keyring second */
 382         if (cred->tgcred->process_keyring) {
 383                 key_ref = keyring_search_aux(
 384                         make_key_ref(cred->tgcred->process_keyring, 1),
 385                         cred, type, description, match, no_state_check);
 386                 if (!IS_ERR(key_ref))
 387                         goto found;
 388
 389                 switch (PTR_ERR(key_ref)) {
 390                 case -EAGAIN: /* no key */
 391                         if (ret)
 392                                 break;
 393                 case -ENOKEY: /* negative key */
 394                         ret = key_ref;
 395                         break;
 396                 default:
 397                         err = key_ref;
 398                         break;
 399                 }
 400         }
 401
 402         /* search the session keyring */
 403         if (cred->tgcred->session_keyring) {
 404                 rcu_read_lock();
 405                 key_ref = keyring_search_aux(
 406                         make_key_ref(rcu_dereference(
 407                                              cred->tgcred->session_keyring),
 408                                      1),
 409                         cred, type, description, match, no_state_check);
 410                 rcu_read_unlock();
 411
 412                 if (!IS_ERR(key_ref))
 413                         goto found;
 414
 415                 switch (PTR_ERR(key_ref)) {
 416                 case -EAGAIN: /* no key */
 417                         if (ret)
 418                                 break;
 419                 case -ENOKEY: /* negative key */
 420                         ret = key_ref;
 421                         break;
 422                 default:
 423                         err = key_ref;
 424                         break;
 425                 }
 426         }
 427         /* or search the user-session keyring */
 428         else if (cred->user->session_keyring) {
 429                 key_ref = keyring_search_aux(
 430                         make_key_ref(cred->user->session_keyring, 1),
 431                         cred, type, description, match, no_state_check);
 432                 if (!IS_ERR(key_ref))
 433                         goto found;
 434
 435                 switch (PTR_ERR(key_ref)) {
 436                 case -EAGAIN: /* no key */
 437                         if (ret)
 438                                 break;
 439                 case -ENOKEY: /* negative key */
 440                         ret = key_ref;
 441                         break;
 442                 default:
 443                         err = key_ref;
 444                         break;
 445                 }
 446         }
 447
 448         /* no key - decide on the error we're going to go for */
 449         key_ref = ret ? ret : err;
 450
 451 found:
 452         return key_ref;
 453 }
 454
 455 /*
 456  * Search the process keyrings attached to the supplied cred for the first
 457  * matching key in the manner of search_my_process_keyrings(), but also search
 458  * the keys attached to the assumed authorisation key using its credentials if
 459  * one is available.
 460  *
 461  * Return same as search_my_process_keyrings().
 462  */
 463 key_ref_t search_process_keyrings(struct key_type *type,
 464                                   const void *description,
 465                                   key_match_func_t match,
 466                                   const struct cred *cred)
 467 {
 468         struct request_key_auth *rka;
 469         key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;
 470
 471         might_sleep();
 472
 473         key_ref = search_my_process_keyrings(type, description, match,
 474                                              false, cred);
 475         if (!IS_ERR(key_ref))
 476                 goto found;
 477         err = key_ref;
 478
 479         /* if this process has an instantiation authorisation key, then we also
 480          * search the keyrings of the process mentioned there
 481          * - we don't permit access to request_key auth keys via this method
 482          */
 483         if (cred->request_key_auth &&
 484             cred == current_cred() &&
 485             type != &key_type_request_key_auth
 486             ) {
 487                 /* defend against the auth key being revoked */
 488                 down_read(&cred->request_key_auth->sem);
 489
 490                 if (key_validate(cred->request_key_auth) == 0) {
 491                         rka = cred->request_key_auth->payload.data;
 492
 493                         key_ref = search_process_keyrings(type, description,
 494                                                           match, rka->cred);
 495
 496                         up_read(&cred->request_key_auth->sem);
 497
 498                         if (!IS_ERR(key_ref))
 499                                 goto found;
 500
 501                         ret = key_ref;
 502                 } else {
 503                         up_read(&cred->request_key_auth->sem);
 504                 }
 505         }
 506
 507         /* no key - decide on the error we're going to go for */
 508         if (err == ERR_PTR(-ENOKEY) || ret == ERR_PTR(-ENOKEY))
 509                 key_ref = ERR_PTR(-ENOKEY);
 510         else if (err == ERR_PTR(-EACCES))
 511                 key_ref = ret;
 512         else
 513                 key_ref = err;
 514
 515 found:
 516         return key_ref;
 517 }
 518
 519 /*
 520  * See if the key we're looking at is the target key.
 521  */
 522 int lookup_user_key_possessed(const struct key *key, const void *target)
 523 {
 524         return key == target;
 525 }
 526
 527 /*
 528  * Look up a key ID given us by userspace with a given permissions mask to get
 529  * the key it refers to.
 530  *
 531  * Flags can be passed to request that special keyrings be created if referred
 532  * to directly, to permit partially constructed keys to be found and to skip
 533  * validity and permission checks on the found key.
 534  *
 535  * Returns a pointer to the key with an incremented usage count if successful;
 536  * -EINVAL if the key ID is invalid; -ENOKEY if the key ID does not correspond
 537  * to a key or the best found key was a negative key; -EKEYREVOKED or
 538  * -EKEYEXPIRED if the best found key was revoked or expired; -EACCES if the
 539  * found key doesn't grant the requested permit or the LSM denied access to it;
 540  * or -ENOMEM if a special keyring couldn't be created.
 541  *
 542  * In the case of a successful return, the possession attribute is set on the
 543  * returned key reference.
 544  */
 545 key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
 546                           key_perm_t perm)
 547 {
 548         struct request_key_auth *rka;
 549         const struct cred *cred;
 550         struct key *key;
 551         key_ref_t key_ref, skey_ref;
 552         int ret;
 553
 554 try_again:
 555         cred = get_current_cred();
 556         key_ref = ERR_PTR(-ENOKEY);
 557
 558         switch (id) {
 559         case KEY_SPEC_THREAD_KEYRING:
 560                 if (!cred->thread_keyring) {
 561                         if (!(lflags & KEY_LOOKUP_CREATE))
 562                                 goto error;
 563
 564                         ret = install_thread_keyring();
 565                         if (ret < 0) {
 566                                 key_ref = ERR_PTR(ret);
 567                                 goto error;
 568                         }
 569                         goto reget_creds;
 570                 }
 571
 572                 key = cred->thread_keyring;
 573                 atomic_inc(&key->usage);
 574                 key_ref = make_key_ref(key, 1);
 575                 break;
 576
 577         case KEY_SPEC_PROCESS_KEYRING:
 578                 if (!cred->tgcred->process_keyring) {
 579                         if (!(lflags & KEY_LOOKUP_CREATE))
 580                                 goto error;
 581
 582                         ret = install_process_keyring();
 583                         if (ret < 0) {
 584                                 key_ref = ERR_PTR(ret);
 585                                 goto error;
 586                         }
 587                         goto reget_creds;
 588                 }
 589
 590                 key = cred->tgcred->process_keyring;
 591                 atomic_inc(&key->usage);
 592                 key_ref = make_key_ref(key, 1);
 593                 break;
 594
 595         case KEY_SPEC_SESSION_KEYRING:
 596                 if (!cred->tgcred->session_keyring) {
 597                         /* always install a session keyring upon access if one
 598                          * doesn't exist yet */
 599                         ret = install_user_keyrings();
 600                         if (ret < 0)
 601                                 goto error;
 602                         if (lflags & KEY_LOOKUP_CREATE)
 603                                 ret = join_session_keyring(NULL);
 604                         else
 605                                 ret = install_session_keyring(
 606                                         cred->user->session_keyring);
 607
 608                         if (ret < 0)
 609                                 goto error;
 610                         goto reget_creds;
 611                 } else if (cred->tgcred->session_keyring ==
 612                            cred->user->session_keyring &&
 613                            lflags & KEY_LOOKUP_CREATE) {
 614                         ret = join_session_keyring(NULL);
 615                         if (ret < 0)
 616                                 goto error;
 617                         goto reget_creds;
 618                 }
 619
 620                 rcu_read_lock();
 621                 key = rcu_dereference(cred->tgcred->session_keyring);
 622                 atomic_inc(&key->usage);
 623                 rcu_read_unlock();
 624                 key_ref = make_key_ref(key, 1);
 625                 break;
 626
 627         case KEY_SPEC_USER_KEYRING:
 628                 if (!cred->user->uid_keyring) {
 629                         ret = install_user_keyrings();
 630                         if (ret < 0)
 631                                 goto error;
 632                 }
 633
 634                 key = cred->user->uid_keyring;
 635                 atomic_inc(&key->usage);
 636                 key_ref = make_key_ref(key, 1);
 637                 break;
 638
 639         case KEY_SPEC_USER_SESSION_KEYRING:
 640                 if (!cred->user->session_keyring) {
 641                         ret = install_user_keyrings();
 642                         if (ret < 0)
 643                                 goto error;
 644                 }
 645
 646                 key = cred->user->session_keyring;
 647                 atomic_inc(&key->usage);
 648                 key_ref = make_key_ref(key, 1);
 649                 break;
 650
 651         case KEY_SPEC_GROUP_KEYRING:
 652                 /* group keyrings are not yet supported */
 653                 key_ref = ERR_PTR(-EINVAL);
 654                 goto error;
 655
 656         case KEY_SPEC_REQKEY_AUTH_KEY:
 657                 key = cred->request_key_auth;
 658                 if (!key)
 659                         goto error;
 660
 661                 atomic_inc(&key->usage);
 662                 key_ref = make_key_ref(key, 1);
 663                 break;
 664
 665         case KEY_SPEC_REQUESTOR_KEYRING:
 666                 if (!cred->request_key_auth)
 667                         goto error;
 668
 669                 down_read(&cred->request_key_auth->sem);
 670                 if (cred->request_key_auth->flags & KEY_FLAG_REVOKED) {
 671                         key_ref = ERR_PTR(-EKEYREVOKED);
 672                         key = NULL;
 673                 } else {
 674                         rka = cred->request_key_auth->payload.data;
 675                         key = rka->dest_keyring;
 676                         atomic_inc(&key->usage);
 677                 }
 678                 up_read(&cred->request_key_auth->sem);
 679                 if (!key)
 680                         goto error;
 681                 key_ref = make_key_ref(key, 1);
 682                 break;
 683
 684         default:
 685                 key_ref = ERR_PTR(-EINVAL);
 686                 if (id < 1)
 687                         goto error;
 688
 689                 key = key_lookup(id);
 690                 if (IS_ERR(key)) {
 691                         key_ref = ERR_CAST(key);
 692                         goto error;
 693                 }
 694
 695                 key_ref = make_key_ref(key, 0);
 696
 697                 /* check to see if we possess the key */
 698                 skey_ref = search_process_keyrings(key->type, key,
 699                                                    lookup_user_key_possessed,
 700                                                    cred);
 701
 702                 if (!IS_ERR(skey_ref)) {
 703                         key_put(key);
 704                         key_ref = skey_ref;
 705                 }
 706
 707                 break;
 708         }
 709
 710         /* unlink does not use the nominated key in any way, so can skip all
 711          * the permission checks as it is only concerned with the keyring */
 712         if (lflags & KEY_LOOKUP_FOR_UNLINK) {
 713                 ret = 0;
 714                 goto error;
 715         }
 716
 717         if (!(lflags & KEY_LOOKUP_PARTIAL)) {
 718                 ret = wait_for_key_construction(key, true);
 719                 switch (ret) {
 720                 case -ERESTARTSYS:
 721                         goto invalid_key;
 722                 default:
 723                         if (perm)
 724                                 goto invalid_key;
 725                 case 0:
 726                         break;
 727                 }
 728         } else if (perm) {
 729                 ret = key_validate(key);
 730                 if (ret < 0)
 731                         goto invalid_key;
 732         }
 733
 734         ret = -EIO;
 735         if (!(lflags & KEY_LOOKUP_PARTIAL) &&
 736             !test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 737                 goto invalid_key;
 738
 739         /* check the permissions */
 740         ret = key_task_permission(key_ref, cred, perm);
 741         if (ret < 0)
 742                 goto invalid_key;
 743
 744 error:
 745         put_cred(cred);
 746         return key_ref;
 747
 748 invalid_key:
 749         key_ref_put(key_ref);
 750         key_ref = ERR_PTR(ret);
 751         goto error;
 752
 753         /* if we attempted to install a keyring, then it may have caused new
 754          * creds to be installed */
 755 reget_creds:
 756         put_cred(cred);
 757         goto try_again;
 758 }
 759
 760 /*
 761  * Join the named keyring as the session keyring if possible else attempt to
 762  * create a new one of that name and join that.
 763  *
 764  * If the name is NULL, an empty anonymous keyring will be installed as the
 765  * session keyring.
 766  *
 767  * Named session keyrings are joined with a semaphore held to prevent the
 768  * keyrings from going away whilst the attempt is made to going them and also
 769  * to prevent a race in creating compatible session keyrings.
 770  */
 771 long join_session_keyring(const char *name)
 772 {
 773         const struct cred *old;
 774         struct cred *new;
 775         struct key *keyring;
 776         long ret, serial;
 777
 778         /* only permit this if there's a single thread in the thread group -
 779          * this avoids us having to adjust the creds on all threads and risking
 780          * ENOMEM */
 781         if (!current_is_single_threaded())
 782                 return -EMLINK;
 783
 784         new = prepare_creds();
 785         if (!new)
 786                 return -ENOMEM;
 787         old = current_cred();
 788
 789         /* if no name is provided, install an anonymous keyring */
 790         if (!name) {
 791                 ret = install_session_keyring_to_cred(new, NULL);
 792                 if (ret < 0)
 793                         goto error;
 794
 795                 serial = new->tgcred->session_keyring->serial;
 796                 ret = commit_creds(new);
 797                 if (ret == 0)
 798                         ret = serial;
 799                 goto okay;
 800         }
 801
 802         /* allow the user to join or create a named keyring */
 803         mutex_lock(&key_session_mutex);
 804
 805         /* look for an existing keyring of this name */
 806         keyring = find_keyring_by_name(name, false);
 807         if (PTR_ERR(keyring) == -ENOKEY) {
 808                 /* not found - try and create a new one */
 809                 keyring = keyring_alloc(name, old->uid, old->gid, old,
 810                                         KEY_ALLOC_IN_QUOTA, NULL);
 811                 if (IS_ERR(keyring)) {
 812                         ret = PTR_ERR(keyring);
 813                         goto error2;
 814                 }
 815         } else if (IS_ERR(keyring)) {
 816                 ret = PTR_ERR(keyring);
 817                 goto error2;
 818         }
 819
 820         /* we've got a keyring - now to install it */
 821         ret = install_session_keyring_to_cred(new, keyring);
 822         if (ret < 0)
 823                 goto error2;
 824
 825         commit_creds(new);
 826         mutex_unlock(&key_session_mutex);
 827
 828         ret = keyring->serial;
 829         key_put(keyring);
 830 okay:
 831         return ret;
 832
 833 error2:
 834         mutex_unlock(&key_session_mutex);
 835 error:
 836         abort_creds(new);
 837         return ret;
 838 }
 839
 840 /*
 841  * Replace a process's session keyring on behalf of one of its children when
 842  * the target  process is about to resume userspace execution.
 843  */
 844 void key_replace_session_keyring(void)
 845 {
 846         const struct cred *old;
 847         struct cred *new;
 848
 849         if (!current->replacement_session_keyring)
 850                 return;
 851
 852         write_lock_irq(&tasklist_lock);
 853         new = current->replacement_session_keyring;
 854         current->replacement_session_keyring = NULL;
 855         write_unlock_irq(&tasklist_lock);
 856
 857         if (!new)
 858                 return;
 859
 860         old = current_cred();
 861         new->  uid      = old->  uid;
 862         new-> euid      = old-> euid;
 863         new-> suid      = old-> suid;
 864         new->fsuid      = old->fsuid;
 865         new->  gid      = old->  gid;
 866         new-> egid      = old-> egid;
 867         new-> sgid      = old-> sgid;
 868         new->fsgid      = old->fsgid;
 869         new->user       = get_uid(old->user);
 870         new->user_ns    = new->user->user_ns;
 871         new->group_info = get_group_info(old->group_info);
 872
 873         new->securebits = old->securebits;
 874         new->cap_inheritable    = old->cap_inheritable;
 875         new->cap_permitted      = old->cap_permitted;
 876         new->cap_effective      = old->cap_effective;
 877         new->cap_bset           = old->cap_bset;
 878
 879         new->jit_keyring        = old->jit_keyring;
 880         new->thread_keyring     = key_get(old->thread_keyring);
 881         new->tgcred->tgid       = old->tgcred->tgid;
 882         new->tgcred->process_keyring = key_get(old->tgcred->process_keyring);
 883
 884         security_transfer_creds(new, old);
 885
 886         commit_creds(new);
 887 }