fs/afs/security.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* AFS security handling
   3  *
   4  * Copyright (C) 2007, 2017 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #include <linux/init.h>
   9 #include <linux/slab.h>
  10 #include <linux/fs.h>
  11 #include <linux/ctype.h>
  12 #include <linux/sched.h>
  13 #include <linux/hashtable.h>
  14 #include <keys/rxrpc-type.h>
  15 #include "internal.h"
  16
  17 static DEFINE_HASHTABLE(afs_permits_cache, 10);
  18 static DEFINE_SPINLOCK(afs_permits_lock);
  19
  20 /*
  21  * get a key
  22  */
  23 struct key *afs_request_key(struct afs_cell *cell)
  24 {
  25         struct key *key;
  26
  27         _enter("{%x}", key_serial(cell->anonymous_key));
  28
  29         _debug("key %s", cell->anonymous_key->description);
  30         key = request_key_net(&key_type_rxrpc, cell->anonymous_key->description,
  31                               cell->net->net, NULL);
  32         if (IS_ERR(key)) {
  33                 if (PTR_ERR(key) != -ENOKEY) {
  34                         _leave(" = %ld", PTR_ERR(key));
  35                         return key;
  36                 }
  37
  38                 /* act as anonymous user */
  39                 _leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
  40                 return key_get(cell->anonymous_key);
  41         } else {
  42                 /* act as authorised user */
  43                 _leave(" = {%x} [auth]", key_serial(key));
  44                 return key;
  45         }
  46 }
  47
  48 /*
  49  * Get a key when pathwalk is in rcuwalk mode.
  50  */
  51 struct key *afs_request_key_rcu(struct afs_cell *cell)
  52 {
  53         struct key *key;
  54
  55         _enter("{%x}", key_serial(cell->anonymous_key));
  56
  57         _debug("key %s", cell->anonymous_key->description);
  58         key = request_key_net_rcu(&key_type_rxrpc,
  59                                   cell->anonymous_key->description,
  60                                   cell->net->net);
  61         if (IS_ERR(key)) {
  62                 if (PTR_ERR(key) != -ENOKEY) {
  63                         _leave(" = %ld", PTR_ERR(key));
  64                         return key;
  65                 }
  66
  67                 /* act as anonymous user */
  68                 _leave(" = {%x} [anon]", key_serial(cell->anonymous_key));
  69                 return key_get(cell->anonymous_key);
  70         } else {
  71                 /* act as authorised user */
  72                 _leave(" = {%x} [auth]", key_serial(key));
  73                 return key;
  74         }
  75 }
  76
  77 /*
  78  * Dispose of a list of permits.
  79  */
  80 static void afs_permits_rcu(struct rcu_head *rcu)
  81 {
  82         struct afs_permits *permits =
  83                 container_of(rcu, struct afs_permits, rcu);
  84         int i;
  85
  86         for (i = 0; i < permits->nr_permits; i++)
  87                 key_put(permits->permits[i].key);
  88         kfree(permits);
  89 }
  90
  91 /*
  92  * Discard a permission cache.
  93  */
  94 void afs_put_permits(struct afs_permits *permits)
  95 {
  96         if (permits && refcount_dec_and_test(&permits->usage)) {
  97                 spin_lock(&afs_permits_lock);
  98                 hash_del_rcu(&permits->hash_node);
  99                 spin_unlock(&afs_permits_lock);
 100                 call_rcu(&permits->rcu, afs_permits_rcu);
 101         }
 102 }
 103
 104 /*
 105  * Clear a permit cache on callback break.
 106  */
 107 void afs_clear_permits(struct afs_vnode *vnode)
 108 {
 109         struct afs_permits *permits;
 110
 111         spin_lock(&vnode->lock);
 112         permits = rcu_dereference_protected(vnode->permit_cache,
 113                                             lockdep_is_held(&vnode->lock));
 114         RCU_INIT_POINTER(vnode->permit_cache, NULL);
 115         spin_unlock(&vnode->lock);
 116
 117         afs_put_permits(permits);
 118 }
 119
 120 /*
 121  * Hash a list of permits.  Use simple addition to make it easy to add an extra
 122  * one at an as-yet indeterminate position in the list.
 123  */
 124 static void afs_hash_permits(struct afs_permits *permits)
 125 {
 126         unsigned long h = permits->nr_permits;
 127         int i;
 128
 129         for (i = 0; i < permits->nr_permits; i++) {
 130                 h += (unsigned long)permits->permits[i].key / sizeof(void *);
 131                 h += permits->permits[i].access;
 132         }
 133
 134         permits->h = h;
 135 }
 136
 137 /*
 138  * Cache the CallerAccess result obtained from doing a fileserver operation
 139  * that returned a vnode status for a particular key.  If a callback break
 140  * occurs whilst the operation was in progress then we have to ditch the cache
 141  * as the ACL *may* have changed.
 142  */
 143 void afs_cache_permit(struct afs_vnode *vnode, struct key *key,
 144                       unsigned int cb_break, struct afs_status_cb *scb)
 145 {
 146         struct afs_permits *permits, *xpermits, *replacement, *zap, *new = NULL;
 147         afs_access_t caller_access = scb->status.caller_access;
 148         size_t size = 0;
 149         bool changed = false;
 150         int i, j;
 151
 152         _enter("{%llx:%llu},%x,%x",
 153                vnode->fid.vid, vnode->fid.vnode, key_serial(key), caller_access);
 154
 155         rcu_read_lock();
 156
 157         /* Check for the common case first: We got back the same access as last
 158          * time we tried and already have it recorded.
 159          */
 160         permits = rcu_dereference(vnode->permit_cache);
 161         if (permits) {
 162                 if (!permits->invalidated) {
 163                         for (i = 0; i < permits->nr_permits; i++) {
 164                                 if (permits->permits[i].key < key)
 165                                         continue;
 166                                 if (permits->permits[i].key > key)
 167                                         break;
 168                                 if (permits->permits[i].access != caller_access) {
 169                                         changed = true;
 170                                         break;
 171                                 }
 172
 173                                 if (afs_cb_is_broken(cb_break, vnode)) {
 174                                         changed = true;
 175                                         break;
 176                                 }
 177
 178                                 /* The cache is still good. */
 179                                 rcu_read_unlock();
 180                                 return;
 181                         }
 182                 }
 183
 184                 changed |= permits->invalidated;
 185                 size = permits->nr_permits;
 186
 187                 /* If this set of permits is now wrong, clear the permits
 188                  * pointer so that no one tries to use the stale information.
 189                  */
 190                 if (changed) {
 191                         spin_lock(&vnode->lock);
 192                         if (permits != rcu_access_pointer(vnode->permit_cache))
 193                                 goto someone_else_changed_it_unlock;
 194                         RCU_INIT_POINTER(vnode->permit_cache, NULL);
 195                         spin_unlock(&vnode->lock);
 196
 197                         afs_put_permits(permits);
 198                         permits = NULL;
 199                         size = 0;
 200                 }
 201         }
 202
 203         if (afs_cb_is_broken(cb_break, vnode))
 204                 goto someone_else_changed_it;
 205
 206         /* We need a ref on any permits list we want to copy as we'll have to
 207          * drop the lock to do memory allocation.
 208          */
 209         if (permits && !refcount_inc_not_zero(&permits->usage))
 210                 goto someone_else_changed_it;
 211
 212         rcu_read_unlock();
 213
 214         /* Speculatively create a new list with the revised permission set.  We
 215          * discard this if we find an extant match already in the hash, but
 216          * it's easier to compare with memcmp this way.
 217          *
 218          * We fill in the key pointers at this time, but we don't get the refs
 219          * yet.
 220          */
 221         size++;
 222         new = kzalloc(struct_size(new, permits, size), GFP_NOFS);
 223         if (!new)
 224                 goto out_put;
 225
 226         refcount_set(&new->usage, 1);
 227         new->nr_permits = size;
 228         i = j = 0;
 229         if (permits) {
 230                 for (i = 0; i < permits->nr_permits; i++) {
 231                         if (j == i && permits->permits[i].key > key) {
 232                                 new->permits[j].key = key;
 233                                 new->permits[j].access = caller_access;
 234                                 j++;
 235                         }
 236                         new->permits[j].key = permits->permits[i].key;
 237                         new->permits[j].access = permits->permits[i].access;
 238                         j++;
 239                 }
 240         }
 241
 242         if (j == i) {
 243                 new->permits[j].key = key;
 244                 new->permits[j].access = caller_access;
 245         }
 246
 247         afs_hash_permits(new);
 248
 249         /* Now see if the permit list we want is actually already available */
 250         spin_lock(&afs_permits_lock);
 251
 252         hash_for_each_possible(afs_permits_cache, xpermits, hash_node, new->h) {
 253                 if (xpermits->h != new->h ||
 254                     xpermits->invalidated ||
 255                     xpermits->nr_permits != new->nr_permits ||
 256                     memcmp(xpermits->permits, new->permits,
 257                            new->nr_permits * sizeof(struct afs_permit)) != 0)
 258                         continue;
 259
 260                 if (refcount_inc_not_zero(&xpermits->usage)) {
 261                         replacement = xpermits;
 262                         goto found;
 263                 }
 264
 265                 break;
 266         }
 267
 268         for (i = 0; i < new->nr_permits; i++)
 269                 key_get(new->permits[i].key);
 270         hash_add_rcu(afs_permits_cache, &new->hash_node, new->h);
 271         replacement = new;
 272         new = NULL;
 273
 274 found:
 275         spin_unlock(&afs_permits_lock);
 276
 277         kfree(new);
 278
 279         rcu_read_lock();
 280         spin_lock(&vnode->lock);
 281         zap = rcu_access_pointer(vnode->permit_cache);
 282         if (!afs_cb_is_broken(cb_break, vnode) && zap == permits)
 283                 rcu_assign_pointer(vnode->permit_cache, replacement);
 284         else
 285                 zap = replacement;
 286         spin_unlock(&vnode->lock);
 287         rcu_read_unlock();
 288         afs_put_permits(zap);
 289 out_put:
 290         afs_put_permits(permits);
 291         return;
 292
 293 someone_else_changed_it_unlock:
 294         spin_unlock(&vnode->lock);
 295 someone_else_changed_it:
 296         /* Someone else changed the cache under us - don't recheck at this
 297          * time.
 298          */
 299         rcu_read_unlock();
 300         return;
 301 }
 302
 303 static bool afs_check_permit_rcu(struct afs_vnode *vnode, struct key *key,
 304                                  afs_access_t *_access)
 305 {
 306         const struct afs_permits *permits;
 307         int i;
 308
 309         _enter("{%llx:%llu},%x",
 310                vnode->fid.vid, vnode->fid.vnode, key_serial(key));
 311
 312         /* check the permits to see if we've got one yet */
 313         if (key == vnode->volume->cell->anonymous_key) {
 314                 *_access = vnode->status.anon_access;
 315                 _leave(" = t [anon %x]", *_access);
 316                 return true;
 317         }
 318
 319         permits = rcu_dereference(vnode->permit_cache);
 320         if (permits) {
 321                 for (i = 0; i < permits->nr_permits; i++) {
 322                         if (permits->permits[i].key < key)
 323                                 continue;
 324                         if (permits->permits[i].key > key)
 325                                 break;
 326
 327                         *_access = permits->permits[i].access;
 328                         _leave(" = %u [perm %x]", !permits->invalidated, *_access);
 329                         return !permits->invalidated;
 330                 }
 331         }
 332
 333         _leave(" = f");
 334         return false;
 335 }
 336
 337 /*
 338  * check with the fileserver to see if the directory or parent directory is
 339  * permitted to be accessed with this authorisation, and if so, what access it
 340  * is granted
 341  */
 342 int afs_check_permit(struct afs_vnode *vnode, struct key *key,
 343                      afs_access_t *_access)
 344 {
 345         struct afs_permits *permits;
 346         bool valid = false;
 347         int i, ret;
 348
 349         _enter("{%llx:%llu},%x",
 350                vnode->fid.vid, vnode->fid.vnode, key_serial(key));
 351
 352         /* check the permits to see if we've got one yet */
 353         if (key == vnode->volume->cell->anonymous_key) {
 354                 _debug("anon");
 355                 *_access = vnode->status.anon_access;
 356                 valid = true;
 357         } else {
 358                 rcu_read_lock();
 359                 permits = rcu_dereference(vnode->permit_cache);
 360                 if (permits) {
 361                         for (i = 0; i < permits->nr_permits; i++) {
 362                                 if (permits->permits[i].key < key)
 363                                         continue;
 364                                 if (permits->permits[i].key > key)
 365                                         break;
 366
 367                                 *_access = permits->permits[i].access;
 368                                 valid = !permits->invalidated;
 369                                 break;
 370                         }
 371                 }
 372                 rcu_read_unlock();
 373         }
 374
 375         if (!valid) {
 376                 /* Check the status on the file we're actually interested in
 377                  * (the post-processing will cache the result).
 378                  */
 379                 _debug("no valid permit");
 380
 381                 ret = afs_fetch_status(vnode, key, false, _access);
 382                 if (ret < 0) {
 383                         *_access = 0;
 384                         _leave(" = %d", ret);
 385                         return ret;
 386                 }
 387         }
 388
 389         _leave(" = 0 [access %x]", *_access);
 390         return 0;
 391 }
 392
 393 /*
 394  * check the permissions on an AFS file
 395  * - AFS ACLs are attached to directories only, and a file is controlled by its
 396  *   parent directory's ACL
 397  */
 398 int afs_permission(struct user_namespace *mnt_userns, struct inode *inode,
 399                    int mask)
 400 {
 401         struct afs_vnode *vnode = AFS_FS_I(inode);
 402         afs_access_t access;
 403         struct key *key;
 404         int ret = 0;
 405
 406         _enter("{{%llx:%llu},%lx},%x,",
 407                vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
 408
 409         if (mask & MAY_NOT_BLOCK) {
 410                 key = afs_request_key_rcu(vnode->volume->cell);
 411                 if (IS_ERR(key))
 412                         return -ECHILD;
 413
 414                 ret = -ECHILD;
 415                 if (!afs_check_validity(vnode) ||
 416                     !afs_check_permit_rcu(vnode, key, &access))
 417                         goto error;
 418         } else {
 419                 key = afs_request_key(vnode->volume->cell);
 420                 if (IS_ERR(key)) {
 421                         _leave(" = %ld [key]", PTR_ERR(key));
 422                         return PTR_ERR(key);
 423                 }
 424
 425                 ret = afs_validate(vnode, key);
 426                 if (ret < 0)
 427                         goto error;
 428
 429                 /* check the permits to see if we've got one yet */
 430                 ret = afs_check_permit(vnode, key, &access);
 431                 if (ret < 0)
 432                         goto error;
 433         }
 434
 435         /* interpret the access mask */
 436         _debug("REQ %x ACC %x on %s",
 437                mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
 438
 439         ret = 0;
 440         if (S_ISDIR(inode->i_mode)) {
 441                 if (mask & (MAY_EXEC | MAY_READ | MAY_CHDIR)) {
 442                         if (!(access & AFS_ACE_LOOKUP))
 443                                 goto permission_denied;
 444                 }
 445                 if (mask & MAY_WRITE) {
 446                         if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
 447                                         AFS_ACE_INSERT))) /* create, mkdir, symlink, rename to */
 448                                 goto permission_denied;
 449                 }
 450         } else {
 451                 if (!(access & AFS_ACE_LOOKUP))
 452                         goto permission_denied;
 453                 if ((mask & MAY_EXEC) && !(inode->i_mode & S_IXUSR))
 454                         goto permission_denied;
 455                 if (mask & (MAY_EXEC | MAY_READ)) {
 456                         if (!(access & AFS_ACE_READ))
 457                                 goto permission_denied;
 458                         if (!(inode->i_mode & S_IRUSR))
 459                                 goto permission_denied;
 460                 } else if (mask & MAY_WRITE) {
 461                         if (!(access & AFS_ACE_WRITE))
 462                                 goto permission_denied;
 463                         if (!(inode->i_mode & S_IWUSR))
 464                                 goto permission_denied;
 465                 }
 466         }
 467
 468         key_put(key);
 469         _leave(" = %d", ret);
 470         return ret;
 471
 472 permission_denied:
 473         ret = -EACCES;
 474 error:
 475         key_put(key);
 476         _leave(" = %d", ret);
 477         return ret;
 478 }
 479
 480 void __exit afs_clean_up_permit_cache(void)
 481 {
 482         int i;
 483
 484         for (i = 0; i < HASH_SIZE(afs_permits_cache); i++)
 485                 WARN_ON_ONCE(!hlist_empty(&afs_permits_cache[i]));
 486
 487 }