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
17static DEFINE_HASHTABLE(afs_permits_cache, 10);
18static DEFINE_SPINLOCK(afs_permits_lock);
19
20/*
21 * get a key
22 */
23struct 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 */
51struct 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 */
80static 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 */
94void 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 */
107void 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 */
124static 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 */
143void 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
274found:
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);
289out_put:
290	afs_put_permits(permits);
291	return;
292
293someone_else_changed_it_unlock:
294	spin_unlock(&vnode->lock);
295someone_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
303static 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 */
342int 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 */
398int 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
472permission_denied:
473	ret = -EACCES;
474error:
475	key_put(key);
476	_leave(" = %d", ret);
477	return ret;
478}
479
480void __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