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 mnt_idmap *idmap, 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 }
488
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