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(sizeof(struct afs_permits) +
 223                       sizeof(struct afs_permit) * size, GFP_NOFS);
 224         if (!new)
 225                 goto out_put;
 226
 227         refcount_set(&new->usage, 1);
 228         new->nr_permits = size;
 229         i = j = 0;
 230         if (permits) {
 231                 for (i = 0; i < permits->nr_permits; i++) {
 232                         if (j == i && permits->permits[i].key > key) {
 233                                 new->permits[j].key = key;
 234                                 new->permits[j].access = caller_access;
 235                                 j++;
 236                         }
 237                         new->permits[j].key = permits->permits[i].key;
 238                         new->permits[j].access = permits->permits[i].access;
 239                         j++;
 240                 }
 241         }
 242
 243         if (j == i) {
 244                 new->permits[j].key = key;
 245                 new->permits[j].access = caller_access;
 246         }
 247
 248         afs_hash_permits(new);
 249
 250         /* Now see if the permit list we want is actually already available */
 251         spin_lock(&afs_permits_lock);
 252
 253         hash_for_each_possible(afs_permits_cache, xpermits, hash_node, new->h) {
 254                 if (xpermits->h != new->h ||
 255                     xpermits->invalidated ||
 256                     xpermits->nr_permits != new->nr_permits ||
 257                     memcmp(xpermits->permits, new->permits,
 258                            new->nr_permits * sizeof(struct afs_permit)) != 0)
 259                         continue;
 260
 261                 if (refcount_inc_not_zero(&xpermits->usage)) {
 262                         replacement = xpermits;
 263                         goto found;
 264                 }
 265
 266                 break;
 267         }
 268
 269         for (i = 0; i < new->nr_permits; i++)
 270                 key_get(new->permits[i].key);
 271         hash_add_rcu(afs_permits_cache, &new->hash_node, new->h);
 272         replacement = new;
 273         new = NULL;
 274
 275 found:
 276         spin_unlock(&afs_permits_lock);
 277
 278         kfree(new);
 279
 280         rcu_read_lock();
 281         spin_lock(&vnode->lock);
 282         zap = rcu_access_pointer(vnode->permit_cache);
 283         if (!afs_cb_is_broken(cb_break, vnode) && zap == permits)
 284                 rcu_assign_pointer(vnode->permit_cache, replacement);
 285         else
 286                 zap = replacement;
 287         spin_unlock(&vnode->lock);
 288         rcu_read_unlock();
 289         afs_put_permits(zap);
 290 out_put:
 291         afs_put_permits(permits);
 292         return;
 293
 294 someone_else_changed_it_unlock:
 295         spin_unlock(&vnode->lock);
 296 someone_else_changed_it:
 297         /* Someone else changed the cache under us - don't recheck at this
 298          * time.
 299          */
 300         rcu_read_unlock();
 301         return;
 302 }
 303
 304 static bool afs_check_permit_rcu(struct afs_vnode *vnode, struct key *key,
 305                                  afs_access_t *_access)
 306 {
 307         const struct afs_permits *permits;
 308         int i;
 309
 310         _enter("{%llx:%llu},%x",
 311                vnode->fid.vid, vnode->fid.vnode, key_serial(key));
 312
 313         /* check the permits to see if we've got one yet */
 314         if (key == vnode->volume->cell->anonymous_key) {
 315                 *_access = vnode->status.anon_access;
 316                 _leave(" = t [anon %x]", *_access);
 317                 return true;
 318         }
 319
 320         permits = rcu_dereference(vnode->permit_cache);
 321         if (permits) {
 322                 for (i = 0; i < permits->nr_permits; i++) {
 323                         if (permits->permits[i].key < key)
 324                                 continue;
 325                         if (permits->permits[i].key > key)
 326                                 break;
 327
 328                         *_access = permits->permits[i].access;
 329                         _leave(" = %u [perm %x]", !permits->invalidated, *_access);
 330                         return !permits->invalidated;
 331                 }
 332         }
 333
 334         _leave(" = f");
 335         return false;
 336 }
 337
 338 /*
 339  * check with the fileserver to see if the directory or parent directory is
 340  * permitted to be accessed with this authorisation, and if so, what access it
 341  * is granted
 342  */
 343 int afs_check_permit(struct afs_vnode *vnode, struct key *key,
 344                      afs_access_t *_access)
 345 {
 346         struct afs_permits *permits;
 347         bool valid = false;
 348         int i, ret;
 349
 350         _enter("{%llx:%llu},%x",
 351                vnode->fid.vid, vnode->fid.vnode, key_serial(key));
 352
 353         /* check the permits to see if we've got one yet */
 354         if (key == vnode->volume->cell->anonymous_key) {
 355                 _debug("anon");
 356                 *_access = vnode->status.anon_access;
 357                 valid = true;
 358         } else {
 359                 rcu_read_lock();
 360                 permits = rcu_dereference(vnode->permit_cache);
 361                 if (permits) {
 362                         for (i = 0; i < permits->nr_permits; i++) {
 363                                 if (permits->permits[i].key < key)
 364                                         continue;
 365                                 if (permits->permits[i].key > key)
 366                                         break;
 367
 368                                 *_access = permits->permits[i].access;
 369                                 valid = !permits->invalidated;
 370                                 break;
 371                         }
 372                 }
 373                 rcu_read_unlock();
 374         }
 375
 376         if (!valid) {
 377                 /* Check the status on the file we're actually interested in
 378                  * (the post-processing will cache the result).
 379                  */
 380                 _debug("no valid permit");
 381
 382                 ret = afs_fetch_status(vnode, key, false, _access);
 383                 if (ret < 0) {
 384                         *_access = 0;
 385                         _leave(" = %d", ret);
 386                         return ret;
 387                 }
 388         }
 389
 390         _leave(" = 0 [access %x]", *_access);
 391         return 0;
 392 }
 393
 394 /*
 395  * check the permissions on an AFS file
 396  * - AFS ACLs are attached to directories only, and a file is controlled by its
 397  *   parent directory's ACL
 398  */
 399 int afs_permission(struct inode *inode, 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 }