fs/afs/security.c

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