GNU Linux-libre 6.1.86-gnu
[releases.git] / 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 }