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 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_fetch_status(vnode, key); 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 } 430