security/keys/process_keys.c

   1 /* Manage a process's keyrings
   2  *
   3  * Copyright (C) 2004-2005, 2008 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/init.h>
  14 #include <linux/sched.h>
  15 #include <linux/keyctl.h>
  16 #include <linux/fs.h>
  17 #include <linux/err.h>
  18 #include <linux/mutex.h>
  19 #include <linux/security.h>
  20 #include <linux/user_namespace.h>
  21 #include <asm/uaccess.h>
  22 #include "internal.h"
  23
  24 /* Session keyring create vs join semaphore */
  25 static DEFINE_MUTEX(key_session_mutex);
  26
  27 /* User keyring creation semaphore */
  28 static DEFINE_MUTEX(key_user_keyring_mutex);
  29
  30 /* The root user's tracking struct */
  31 struct key_user root_key_user = {
  32         .usage          = ATOMIC_INIT(3),
  33         .cons_lock      = __MUTEX_INITIALIZER(root_key_user.cons_lock),
  34         .lock           = __SPIN_LOCK_UNLOCKED(root_key_user.lock),
  35         .nkeys          = ATOMIC_INIT(2),
  36         .nikeys         = ATOMIC_INIT(2),
  37         .uid            = GLOBAL_ROOT_UID,
  38 };
  39
  40 /*
  41  * Install the user and user session keyrings for the current process's UID.
  42  */
  43 int install_user_keyrings(void)
  44 {
  45         struct user_struct *user;
  46         const struct cred *cred;
  47         struct key *uid_keyring, *session_keyring;
  48         key_perm_t user_keyring_perm;
  49         char buf[20];
  50         int ret;
  51         uid_t uid;
  52
  53         user_keyring_perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_ALL;
  54         cred = current_cred();
  55         user = cred->user;
  56         uid = from_kuid(cred->user_ns, user->uid);
  57
  58         kenter("%p{%u}", user, uid);
  59
  60         if (user->uid_keyring && user->session_keyring) {
  61                 kleave(" = 0 [exist]");
  62                 return 0;
  63         }
  64
  65         mutex_lock(&key_user_keyring_mutex);
  66         ret = 0;
  67
  68         if (!user->uid_keyring) {
  69                 /* get the UID-specific keyring
  70                  * - there may be one in existence already as it may have been
  71                  *   pinned by a session, but the user_struct pointing to it
  72                  *   may have been destroyed by setuid */
  73                 sprintf(buf, "_uid.%u", uid);
  74
  75                 uid_keyring = find_keyring_by_name(buf, true);
  76                 if (IS_ERR(uid_keyring)) {
  77                         uid_keyring = keyring_alloc(buf, user->uid, INVALID_GID,
  78                                                     cred, user_keyring_perm,
  79                                                     KEY_ALLOC_IN_QUOTA, NULL);
  80                         if (IS_ERR(uid_keyring)) {
  81                                 ret = PTR_ERR(uid_keyring);
  82                                 goto error;
  83                         }
  84                 }
  85
  86                 /* get a default session keyring (which might also exist
  87                  * already) */
  88                 sprintf(buf, "_uid_ses.%u", uid);
  89
  90                 session_keyring = find_keyring_by_name(buf, true);
  91                 if (IS_ERR(session_keyring)) {
  92                         session_keyring =
  93                                 keyring_alloc(buf, user->uid, INVALID_GID,
  94                                               cred, user_keyring_perm,
  95                                               KEY_ALLOC_IN_QUOTA, NULL);
  96                         if (IS_ERR(session_keyring)) {
  97                                 ret = PTR_ERR(session_keyring);
  98                                 goto error_release;
  99                         }
 100
 101                         /* we install a link from the user session keyring to
 102                          * the user keyring */
 103                         ret = key_link(session_keyring, uid_keyring);
 104                         if (ret < 0)
 105                                 goto error_release_both;
 106                 }
 107
 108                 /* install the keyrings */
 109                 user->uid_keyring = uid_keyring;
 110                 user->session_keyring = session_keyring;
 111         }
 112
 113         mutex_unlock(&key_user_keyring_mutex);
 114         kleave(" = 0");
 115         return 0;
 116
 117 error_release_both:
 118         key_put(session_keyring);
 119 error_release:
 120         key_put(uid_keyring);
 121 error:
 122         mutex_unlock(&key_user_keyring_mutex);
 123         kleave(" = %d", ret);
 124         return ret;
 125 }
 126
 127 /*
 128  * Install a fresh thread keyring directly to new credentials.  This keyring is
 129  * allowed to overrun the quota.
 130  */
 131 int install_thread_keyring_to_cred(struct cred *new)
 132 {
 133         struct key *keyring;
 134
 135         keyring = keyring_alloc("_tid", new->uid, new->gid, new,
 136                                 KEY_POS_ALL | KEY_USR_VIEW,
 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 fresh thread keyring, discarding the old one.
 147  */
 148 static int install_thread_keyring(void)
 149 {
 150         struct cred *new;
 151         int ret;
 152
 153         new = prepare_creds();
 154         if (!new)
 155                 return -ENOMEM;
 156
 157         BUG_ON(new->thread_keyring);
 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 directly to a credentials struct.
 170  *
 171  * Returns -EEXIST if there was already a process keyring, 0 if one installed,
 172  * and other value on any other error
 173  */
 174 int install_process_keyring_to_cred(struct cred *new)
 175 {
 176         struct key *keyring;
 177
 178         if (new->process_keyring)
 179                 return -EEXIST;
 180
 181         keyring = keyring_alloc("_pid", new->uid, new->gid, new,
 182                                 KEY_POS_ALL | KEY_USR_VIEW,
 183                                 KEY_ALLOC_QUOTA_OVERRUN, NULL);
 184         if (IS_ERR(keyring))
 185                 return PTR_ERR(keyring);
 186
 187         new->process_keyring = keyring;
 188         return 0;
 189 }
 190
 191 /*
 192  * Make sure a process keyring is installed for the current process.  The
 193  * existing process keyring is not replaced.
 194  *
 195  * Returns 0 if there is a process keyring by the end of this function, some
 196  * error otherwise.
 197  */
 198 static int install_process_keyring(void)
 199 {
 200         struct cred *new;
 201         int ret;
 202
 203         new = prepare_creds();
 204         if (!new)
 205                 return -ENOMEM;
 206
 207         ret = install_process_keyring_to_cred(new);
 208         if (ret < 0) {
 209                 abort_creds(new);
 210                 return ret != -EEXIST ? ret : 0;
 211         }
 212
 213         return commit_creds(new);
 214 }
 215
 216 /*
 217  * Install a session keyring directly to a credentials struct.
 218  */
 219 int install_session_keyring_to_cred(struct cred *cred, struct key *keyring)
 220 {
 221         unsigned long flags;
 222         struct key *old;
 223
 224         might_sleep();
 225
 226         /* create an empty session keyring */
 227         if (!keyring) {
 228                 flags = KEY_ALLOC_QUOTA_OVERRUN;
 229                 if (cred->session_keyring)
 230                         flags = KEY_ALLOC_IN_QUOTA;
 231
 232                 keyring = keyring_alloc("_ses", cred->uid, cred->gid, cred,
 233                                         KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ,
 234                                         flags, NULL);
 235                 if (IS_ERR(keyring))
 236                         return PTR_ERR(keyring);
 237         } else {
 238                 atomic_inc(&keyring->usage);
 239         }
 240
 241         /* install the keyring */
 242         old = cred->session_keyring;
 243         rcu_assign_pointer(cred->session_keyring, keyring);
 244
 245         if (old)
 246                 key_put(old);
 247
 248         return 0;
 249 }
 250
 251 /*
 252  * Install a session keyring, discarding the old one.  If a keyring is not
 253  * supplied, an empty one is invented.
 254  */
 255 static int install_session_keyring(struct key *keyring)
 256 {
 257         struct cred *new;
 258         int ret;
 259
 260         new = prepare_creds();
 261         if (!new)
 262                 return -ENOMEM;
 263
 264         ret = install_session_keyring_to_cred(new, keyring);
 265         if (ret < 0) {
 266                 abort_creds(new);
 267                 return ret;
 268         }
 269
 270         return commit_creds(new);
 271 }
 272
 273 /*
 274  * Handle the fsuid changing.
 275  */
 276 void key_fsuid_changed(struct task_struct *tsk)
 277 {
 278         /* update the ownership of the thread keyring */
 279         BUG_ON(!tsk->cred);
 280         if (tsk->cred->thread_keyring) {
 281                 down_write(&tsk->cred->thread_keyring->sem);
 282                 tsk->cred->thread_keyring->uid = tsk->cred->fsuid;
 283                 up_write(&tsk->cred->thread_keyring->sem);
 284         }
 285 }
 286
 287 /*
 288  * Handle the fsgid changing.
 289  */
 290 void key_fsgid_changed(struct task_struct *tsk)
 291 {
 292         /* update the ownership of the thread keyring */
 293         BUG_ON(!tsk->cred);
 294         if (tsk->cred->thread_keyring) {
 295                 down_write(&tsk->cred->thread_keyring->sem);
 296                 tsk->cred->thread_keyring->gid = tsk->cred->fsgid;
 297                 up_write(&tsk->cred->thread_keyring->sem);
 298         }
 299 }
 300
 301 /*
 302  * Search the process keyrings attached to the supplied cred for the first
 303  * matching key.
 304  *
 305  * The search criteria are the type and the match function.  The description is
 306  * given to the match function as a parameter, but doesn't otherwise influence
 307  * the search.  Typically the match function will compare the description
 308  * parameter to the key's description.
 309  *
 310  * This can only search keyrings that grant Search permission to the supplied
 311  * credentials.  Keyrings linked to searched keyrings will also be searched if
 312  * they grant Search permission too.  Keys can only be found if they grant
 313  * Search permission to the credentials.
 314  *
 315  * Returns a pointer to the key with the key usage count incremented if
 316  * successful, -EAGAIN if we didn't find any matching key or -ENOKEY if we only
 317  * matched negative keys.
 318  *
 319  * In the case of a successful return, the possession attribute is set on the
 320  * returned key reference.
 321  */
 322 key_ref_t search_my_process_keyrings(struct key_type *type,
 323                                      const void *description,
 324                                      key_match_func_t match,
 325                                      bool no_state_check,
 326                                      const struct cred *cred)
 327 {
 328         key_ref_t key_ref, ret, err;
 329
 330         /* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
 331          * searchable, but we failed to find a key or we found a negative key;
 332          * otherwise we want to return a sample error (probably -EACCES) if
 333          * none of the keyrings were searchable
 334          *
 335          * in terms of priority: success > -ENOKEY > -EAGAIN > other error
 336          */
 337         key_ref = NULL;
 338         ret = NULL;
 339         err = ERR_PTR(-EAGAIN);
 340
 341         /* search the thread keyring first */
 342         if (cred->thread_keyring) {
 343                 key_ref = keyring_search_aux(
 344                         make_key_ref(cred->thread_keyring, 1),
 345                         cred, type, description, match, no_state_check);
 346                 if (!IS_ERR(key_ref))
 347                         goto found;
 348
 349                 switch (PTR_ERR(key_ref)) {
 350                 case -EAGAIN: /* no key */
 351                 case -ENOKEY: /* negative key */
 352                         ret = key_ref;
 353                         break;
 354                 default:
 355                         err = key_ref;
 356                         break;
 357                 }
 358         }
 359
 360         /* search the process keyring second */
 361         if (cred->process_keyring) {
 362                 key_ref = keyring_search_aux(
 363                         make_key_ref(cred->process_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 session keyring */
 382         if (cred->session_keyring) {
 383                 rcu_read_lock();
 384                 key_ref = keyring_search_aux(
 385                         make_key_ref(rcu_dereference(cred->session_keyring), 1),
 386                         cred, type, description, match, no_state_check);
 387                 rcu_read_unlock();
 388
 389                 if (!IS_ERR(key_ref))
 390                         goto found;
 391
 392                 switch (PTR_ERR(key_ref)) {
 393                 case -EAGAIN: /* no key */
 394                         if (ret)
 395                                 break;
 396                 case -ENOKEY: /* negative key */
 397                         ret = key_ref;
 398                         break;
 399                 default:
 400                         err = key_ref;
 401                         break;
 402                 }
 403         }
 404         /* or search the user-session keyring */
 405         else if (cred->user->session_keyring) {
 406                 key_ref = keyring_search_aux(
 407                         make_key_ref(cred->user->session_keyring, 1),
 408                         cred, type, description, match, no_state_check);
 409                 if (!IS_ERR(key_ref))
 410                         goto found;
 411
 412                 switch (PTR_ERR(key_ref)) {
 413                 case -EAGAIN: /* no key */
 414                         if (ret)
 415                                 break;
 416                 case -ENOKEY: /* negative key */
 417                         ret = key_ref;
 418                         break;
 419                 default:
 420                         err = key_ref;
 421                         break;
 422                 }
 423         }
 424
 425         /* no key - decide on the error we're going to go for */
 426         key_ref = ret ? ret : err;
 427
 428 found:
 429         return key_ref;
 430 }
 431
 432 /*
 433  * Search the process keyrings attached to the supplied cred for the first
 434  * matching key in the manner of search_my_process_keyrings(), but also search
 435  * the keys attached to the assumed authorisation key using its credentials if
 436  * one is available.
 437  *
 438  * Return same as search_my_process_keyrings().
 439  */
 440 key_ref_t search_process_keyrings(struct key_type *type,
 441                                   const void *description,
 442                                   key_match_func_t match,
 443                                   const struct cred *cred)
 444 {
 445         struct request_key_auth *rka;
 446         key_ref_t key_ref, ret = ERR_PTR(-EACCES), err;
 447
 448         might_sleep();
 449
 450         key_ref = search_my_process_keyrings(type, description, match,
 451                                              false, cred);
 452         if (!IS_ERR(key_ref))
 453                 goto found;
 454         err = key_ref;
 455
 456         /* if this process has an instantiation authorisation key, then we also
 457          * search the keyrings of the process mentioned there
 458          * - we don't permit access to request_key auth keys via this method
 459          */
 460         if (cred->request_key_auth &&
 461             cred == current_cred() &&
 462             type != &key_type_request_key_auth
 463             ) {
 464                 /* defend against the auth key being revoked */
 465                 down_read(&cred->request_key_auth->sem);
 466
 467                 if (key_validate(cred->request_key_auth) == 0) {
 468                         rka = cred->request_key_auth->payload.data;
 469
 470                         key_ref = search_process_keyrings(type, description,
 471                                                           match, rka->cred);
 472
 473                         up_read(&cred->request_key_auth->sem);
 474
 475                         if (!IS_ERR(key_ref))
 476                                 goto found;
 477
 478                         ret = key_ref;
 479                 } else {
 480                         up_read(&cred->request_key_auth->sem);
 481                 }
 482         }
 483
 484         /* no key - decide on the error we're going to go for */
 485         if (err == ERR_PTR(-ENOKEY) || ret == ERR_PTR(-ENOKEY))
 486                 key_ref = ERR_PTR(-ENOKEY);
 487         else if (err == ERR_PTR(-EACCES))
 488                 key_ref = ret;
 489         else
 490                 key_ref = err;
 491
 492 found:
 493         return key_ref;
 494 }
 495
 496 /*
 497  * See if the key we're looking at is the target key.
 498  */
 499 int lookup_user_key_possessed(const struct key *key, const void *target)
 500 {
 501         return key == target;
 502 }
 503
 504 /*
 505  * Look up a key ID given us by userspace with a given permissions mask to get
 506  * the key it refers to.
 507  *
 508  * Flags can be passed to request that special keyrings be created if referred
 509  * to directly, to permit partially constructed keys to be found and to skip
 510  * validity and permission checks on the found key.
 511  *
 512  * Returns a pointer to the key with an incremented usage count if successful;
 513  * -EINVAL if the key ID is invalid; -ENOKEY if the key ID does not correspond
 514  * to a key or the best found key was a negative key; -EKEYREVOKED or
 515  * -EKEYEXPIRED if the best found key was revoked or expired; -EACCES if the
 516  * found key doesn't grant the requested permit or the LSM denied access to it;
 517  * or -ENOMEM if a special keyring couldn't be created.
 518  *
 519  * In the case of a successful return, the possession attribute is set on the
 520  * returned key reference.
 521  */
 522 key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
 523                           key_perm_t perm)
 524 {
 525         struct request_key_auth *rka;
 526         const struct cred *cred;
 527         struct key *key;
 528         key_ref_t key_ref, skey_ref;
 529         int ret;
 530
 531 try_again:
 532         cred = get_current_cred();
 533         key_ref = ERR_PTR(-ENOKEY);
 534
 535         switch (id) {
 536         case KEY_SPEC_THREAD_KEYRING:
 537                 if (!cred->thread_keyring) {
 538                         if (!(lflags & KEY_LOOKUP_CREATE))
 539                                 goto error;
 540
 541                         ret = install_thread_keyring();
 542                         if (ret < 0) {
 543                                 key_ref = ERR_PTR(ret);
 544                                 goto error;
 545                         }
 546                         goto reget_creds;
 547                 }
 548
 549                 key = cred->thread_keyring;
 550                 atomic_inc(&key->usage);
 551                 key_ref = make_key_ref(key, 1);
 552                 break;
 553
 554         case KEY_SPEC_PROCESS_KEYRING:
 555                 if (!cred->process_keyring) {
 556                         if (!(lflags & KEY_LOOKUP_CREATE))
 557                                 goto error;
 558
 559                         ret = install_process_keyring();
 560                         if (ret < 0) {
 561                                 key_ref = ERR_PTR(ret);
 562                                 goto error;
 563                         }
 564                         goto reget_creds;
 565                 }
 566
 567                 key = cred->process_keyring;
 568                 atomic_inc(&key->usage);
 569                 key_ref = make_key_ref(key, 1);
 570                 break;
 571
 572         case KEY_SPEC_SESSION_KEYRING:
 573                 if (!cred->session_keyring) {
 574                         /* always install a session keyring upon access if one
 575                          * doesn't exist yet */
 576                         ret = install_user_keyrings();
 577                         if (ret < 0)
 578                                 goto error;
 579                         if (lflags & KEY_LOOKUP_CREATE)
 580                                 ret = join_session_keyring(NULL);
 581                         else
 582                                 ret = install_session_keyring(
 583                                         cred->user->session_keyring);
 584
 585                         if (ret < 0)
 586                                 goto error;
 587                         goto reget_creds;
 588                 } else if (cred->session_keyring ==
 589                            cred->user->session_keyring &&
 590                            lflags & KEY_LOOKUP_CREATE) {
 591                         ret = join_session_keyring(NULL);
 592                         if (ret < 0)
 593                                 goto error;
 594                         goto reget_creds;
 595                 }
 596
 597                 rcu_read_lock();
 598                 key = rcu_dereference(cred->session_keyring);
 599                 atomic_inc(&key->usage);
 600                 rcu_read_unlock();
 601                 key_ref = make_key_ref(key, 1);
 602                 break;
 603
 604         case KEY_SPEC_USER_KEYRING:
 605                 if (!cred->user->uid_keyring) {
 606                         ret = install_user_keyrings();
 607                         if (ret < 0)
 608                                 goto error;
 609                 }
 610
 611                 key = cred->user->uid_keyring;
 612                 atomic_inc(&key->usage);
 613                 key_ref = make_key_ref(key, 1);
 614                 break;
 615
 616         case KEY_SPEC_USER_SESSION_KEYRING:
 617                 if (!cred->user->session_keyring) {
 618                         ret = install_user_keyrings();
 619                         if (ret < 0)
 620                                 goto error;
 621                 }
 622
 623                 key = cred->user->session_keyring;
 624                 atomic_inc(&key->usage);
 625                 key_ref = make_key_ref(key, 1);
 626                 break;
 627
 628         case KEY_SPEC_GROUP_KEYRING:
 629                 /* group keyrings are not yet supported */
 630                 key_ref = ERR_PTR(-EINVAL);
 631                 goto error;
 632
 633         case KEY_SPEC_REQKEY_AUTH_KEY:
 634                 key = cred->request_key_auth;
 635                 if (!key)
 636                         goto error;
 637
 638                 atomic_inc(&key->usage);
 639                 key_ref = make_key_ref(key, 1);
 640                 break;
 641
 642         case KEY_SPEC_REQUESTOR_KEYRING:
 643                 if (!cred->request_key_auth)
 644                         goto error;
 645
 646                 down_read(&cred->request_key_auth->sem);
 647                 if (test_bit(KEY_FLAG_REVOKED,
 648                              &cred->request_key_auth->flags)) {
 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         key->last_used_at = current_kernel_time().tv_sec;
 723
 724 error:
 725         put_cred(cred);
 726         return key_ref;
 727
 728 invalid_key:
 729         key_ref_put(key_ref);
 730         key_ref = ERR_PTR(ret);
 731         goto error;
 732
 733         /* if we attempted to install a keyring, then it may have caused new
 734          * creds to be installed */
 735 reget_creds:
 736         put_cred(cred);
 737         goto try_again;
 738 }
 739
 740 /*
 741  * Join the named keyring as the session keyring if possible else attempt to
 742  * create a new one of that name and join that.
 743  *
 744  * If the name is NULL, an empty anonymous keyring will be installed as the
 745  * session keyring.
 746  *
 747  * Named session keyrings are joined with a semaphore held to prevent the
 748  * keyrings from going away whilst the attempt is made to going them and also
 749  * to prevent a race in creating compatible session keyrings.
 750  */
 751 long join_session_keyring(const char *name)
 752 {
 753         const struct cred *old;
 754         struct cred *new;
 755         struct key *keyring;
 756         long ret, serial;
 757
 758         new = prepare_creds();
 759         if (!new)
 760                 return -ENOMEM;
 761         old = current_cred();
 762
 763         /* if no name is provided, install an anonymous keyring */
 764         if (!name) {
 765                 ret = install_session_keyring_to_cred(new, NULL);
 766                 if (ret < 0)
 767                         goto error;
 768
 769                 serial = new->session_keyring->serial;
 770                 ret = commit_creds(new);
 771                 if (ret == 0)
 772                         ret = serial;
 773                 goto okay;
 774         }
 775
 776         /* allow the user to join or create a named keyring */
 777         mutex_lock(&key_session_mutex);
 778
 779         /* look for an existing keyring of this name */
 780         keyring = find_keyring_by_name(name, false);
 781         if (PTR_ERR(keyring) == -ENOKEY) {
 782                 /* not found - try and create a new one */
 783                 keyring = keyring_alloc(
 784                         name, old->uid, old->gid, old,
 785                         KEY_POS_ALL | KEY_USR_VIEW | KEY_USR_READ | KEY_USR_LINK,
 786                         KEY_ALLOC_IN_QUOTA, NULL);
 787                 if (IS_ERR(keyring)) {
 788                         ret = PTR_ERR(keyring);
 789                         goto error2;
 790                 }
 791         } else if (IS_ERR(keyring)) {
 792                 ret = PTR_ERR(keyring);
 793                 goto error2;
 794         } else if (keyring == new->session_keyring) {
 795                 ret = 0;
 796                 goto error2;
 797         }
 798
 799         /* we've got a keyring - now to install it */
 800         ret = install_session_keyring_to_cred(new, keyring);
 801         if (ret < 0)
 802                 goto error2;
 803
 804         commit_creds(new);
 805         mutex_unlock(&key_session_mutex);
 806
 807         ret = keyring->serial;
 808         key_put(keyring);
 809 okay:
 810         return ret;
 811
 812 error2:
 813         mutex_unlock(&key_session_mutex);
 814 error:
 815         abort_creds(new);
 816         return ret;
 817 }
 818
 819 /*
 820  * Replace a process's session keyring on behalf of one of its children when
 821  * the target  process is about to resume userspace execution.
 822  */
 823 void key_change_session_keyring(struct callback_head *twork)
 824 {
 825         const struct cred *old = current_cred();
 826         struct cred *new = container_of(twork, struct cred, rcu);
 827
 828         if (unlikely(current->flags & PF_EXITING)) {
 829                 put_cred(new);
 830                 return;
 831         }
 832
 833         new->  uid      = old->  uid;
 834         new-> euid      = old-> euid;
 835         new-> suid      = old-> suid;
 836         new->fsuid      = old->fsuid;
 837         new->  gid      = old->  gid;
 838         new-> egid      = old-> egid;
 839         new-> sgid      = old-> sgid;
 840         new->fsgid      = old->fsgid;
 841         new->user       = get_uid(old->user);
 842         new->user_ns    = get_user_ns(old->user_ns);
 843         new->group_info = get_group_info(old->group_info);
 844
 845         new->securebits = old->securebits;
 846         new->cap_inheritable    = old->cap_inheritable;
 847         new->cap_permitted      = old->cap_permitted;
 848         new->cap_effective      = old->cap_effective;
 849         new->cap_bset           = old->cap_bset;
 850
 851         new->jit_keyring        = old->jit_keyring;
 852         new->thread_keyring     = key_get(old->thread_keyring);
 853         new->process_keyring    = key_get(old->process_keyring);
 854
 855         security_transfer_creds(new, old);
 856
 857         commit_creds(new);
 858 }