1/* AFS security handling
2 *
3 * Copyright (C) 2007 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 <keys/rxrpc-type.h>
18#include "internal.h"
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(&key_type_rxrpc, cell->anonymous_key->description,
31			  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 * dispose of a permits list
50 */
51void afs_zap_permits(struct rcu_head *rcu)
52{
53	struct afs_permits *permits =
54		container_of(rcu, struct afs_permits, rcu);
55	int loop;
56
57	_enter("{%d}", permits->count);
58
59	for (loop = permits->count - 1; loop >= 0; loop--)
60		key_put(permits->permits[loop].key);
61	kfree(permits);
62}
63
64/*
65 * dispose of a permits list in which all the key pointers have been copied
66 */
67static void afs_dispose_of_permits(struct rcu_head *rcu)
68{
69	struct afs_permits *permits =
70		container_of(rcu, struct afs_permits, rcu);
71
72	_enter("{%d}", permits->count);
73
74	kfree(permits);
75}
76
77/*
78 * get the authorising vnode - this is the specified inode itself if it's a
79 * directory or it's the parent directory if the specified inode is a file or
80 * symlink
81 * - the caller must release the ref on the inode
82 */
83static struct afs_vnode *afs_get_auth_inode(struct afs_vnode *vnode,
84					    struct key *key)
85{
86	struct afs_vnode *auth_vnode;
87	struct inode *auth_inode;
88
89	_enter("");
90
91	if (S_ISDIR(vnode->vfs_inode.i_mode)) {
92		auth_inode = igrab(&vnode->vfs_inode);
93		ASSERT(auth_inode != NULL);
94	} else {
95		auth_inode = afs_iget(vnode->vfs_inode.i_sb, key,
96				      &vnode->status.parent, NULL, NULL);
97		if (IS_ERR(auth_inode))
98			return ERR_PTR(PTR_ERR(auth_inode));
99	}
100
101	auth_vnode = AFS_FS_I(auth_inode);
102	_leave(" = {%x}", auth_vnode->fid.vnode);
103	return auth_vnode;
104}
105
106/*
107 * clear the permit cache on a directory vnode
108 */
109void afs_clear_permits(struct afs_vnode *vnode)
110{
111	struct afs_permits *permits;
112
113	_enter("{%x:%u}", vnode->fid.vid, vnode->fid.vnode);
114
115	mutex_lock(&vnode->permits_lock);
116	permits = vnode->permits;
117	rcu_assign_pointer(vnode->permits, NULL);
118	mutex_unlock(&vnode->permits_lock);
119
120	if (permits)
121		call_rcu(&permits->rcu, afs_zap_permits);
122	_leave("");
123}
124
125/*
126 * add the result obtained for a vnode to its or its parent directory's cache
127 * for the key used to access it
128 */
129void afs_cache_permit(struct afs_vnode *vnode, struct key *key, long acl_order)
130{
131	struct afs_permits *permits, *xpermits;
132	struct afs_permit *permit;
133	struct afs_vnode *auth_vnode;
134	int count, loop;
135
136	_enter("{%x:%u},%x,%lx",
137	       vnode->fid.vid, vnode->fid.vnode, key_serial(key), acl_order);
138
139	auth_vnode = afs_get_auth_inode(vnode, key);
140	if (IS_ERR(auth_vnode)) {
141		_leave(" [get error %ld]", PTR_ERR(auth_vnode));
142		return;
143	}
144
145	mutex_lock(&auth_vnode->permits_lock);
146
147	/* guard against a rename being detected whilst we waited for the
148	 * lock */
149	if (memcmp(&auth_vnode->fid, &vnode->status.parent,
150		   sizeof(struct afs_fid)) != 0) {
151		_debug("renamed");
152		goto out_unlock;
153	}
154
155	/* have to be careful as the directory's callback may be broken between
156	 * us receiving the status we're trying to cache and us getting the
157	 * lock to update the cache for the status */
158	if (auth_vnode->acl_order - acl_order > 0) {
159		_debug("ACL changed?");
160		goto out_unlock;
161	}
162
163	/* always update the anonymous mask */
164	_debug("anon access %x", vnode->status.anon_access);
165	auth_vnode->status.anon_access = vnode->status.anon_access;
166	if (key == vnode->volume->cell->anonymous_key)
167		goto out_unlock;
168
169	xpermits = auth_vnode->permits;
170	count = 0;
171	if (xpermits) {
172		/* see if the permit is already in the list
173		 * - if it is then we just amend the list
174		 */
175		count = xpermits->count;
176		permit = xpermits->permits;
177		for (loop = count; loop > 0; loop--) {
178			if (permit->key == key) {
179				permit->access_mask =
180					vnode->status.caller_access;
181				goto out_unlock;
182			}
183			permit++;
184		}
185	}
186
187	permits = kmalloc(sizeof(*permits) + sizeof(*permit) * (count + 1),
188			  GFP_NOFS);
189	if (!permits)
190		goto out_unlock;
191
192	memcpy(permits->permits, xpermits->permits,
193	       count * sizeof(struct afs_permit));
194
195	_debug("key %x access %x",
196	       key_serial(key), vnode->status.caller_access);
197	permits->permits[count].access_mask = vnode->status.caller_access;
198	permits->permits[count].key = key_get(key);
199	permits->count = count + 1;
200
201	rcu_assign_pointer(auth_vnode->permits, permits);
202	if (xpermits)
203		call_rcu(&xpermits->rcu, afs_dispose_of_permits);
204
205out_unlock:
206	mutex_unlock(&auth_vnode->permits_lock);
207	iput(&auth_vnode->vfs_inode);
208	_leave("");
209}
210
211/*
212 * check with the fileserver to see if the directory or parent directory is
213 * permitted to be accessed with this authorisation, and if so, what access it
214 * is granted
215 */
216static int afs_check_permit(struct afs_vnode *vnode, struct key *key,
217			    afs_access_t *_access)
218{
219	struct afs_permits *permits;
220	struct afs_permit *permit;
221	struct afs_vnode *auth_vnode;
222	bool valid;
223	int loop, ret;
224
225	_enter("{%x:%u},%x",
226	       vnode->fid.vid, vnode->fid.vnode, key_serial(key));
227
228	auth_vnode = afs_get_auth_inode(vnode, key);
229	if (IS_ERR(auth_vnode)) {
230		*_access = 0;
231		_leave(" = %ld", PTR_ERR(auth_vnode));
232		return PTR_ERR(auth_vnode);
233	}
234
235	ASSERT(S_ISDIR(auth_vnode->vfs_inode.i_mode));
236
237	/* check the permits to see if we've got one yet */
238	if (key == auth_vnode->volume->cell->anonymous_key) {
239		_debug("anon");
240		*_access = auth_vnode->status.anon_access;
241		valid = true;
242	} else {
243		valid = false;
244		rcu_read_lock();
245		permits = rcu_dereference(auth_vnode->permits);
246		if (permits) {
247			permit = permits->permits;
248			for (loop = permits->count; loop > 0; loop--) {
249				if (permit->key == key) {
250					_debug("found in cache");
251					*_access = permit->access_mask;
252					valid = true;
253					break;
254				}
255				permit++;
256			}
257		}
258		rcu_read_unlock();
259	}
260
261	if (!valid) {
262		/* check the status on the file we're actually interested in
263		 * (the post-processing will cache the result on auth_vnode) */
264		_debug("no valid permit");
265
266		set_bit(AFS_VNODE_CB_BROKEN, &vnode->flags);
267		ret = afs_vnode_fetch_status(vnode, auth_vnode, key);
268		if (ret < 0) {
269			iput(&auth_vnode->vfs_inode);
270			*_access = 0;
271			_leave(" = %d", ret);
272			return ret;
273		}
274		*_access = vnode->status.caller_access;
275	}
276
277	iput(&auth_vnode->vfs_inode);
278	_leave(" = 0 [access %x]", *_access);
279	return 0;
280}
281
282/*
283 * check the permissions on an AFS file
284 * - AFS ACLs are attached to directories only, and a file is controlled by its
285 *   parent directory's ACL
286 */
287int afs_permission(struct inode *inode, int mask, struct nameidata *nd)
288{
289	struct afs_vnode *vnode = AFS_FS_I(inode);
290	afs_access_t access;
291	struct key *key;
292	int ret;
293
294	_enter("{{%x:%u},%lx},%x,",
295	       vnode->fid.vid, vnode->fid.vnode, vnode->flags, mask);
296
297	key = afs_request_key(vnode->volume->cell);
298	if (IS_ERR(key)) {
299		_leave(" = %ld [key]", PTR_ERR(key));
300		return PTR_ERR(key);
301	}
302
303	/* if the promise has expired, we need to check the server again */
304	if (!vnode->cb_promised) {
305		_debug("not promised");
306		ret = afs_vnode_fetch_status(vnode, NULL, key);
307		if (ret < 0)
308			goto error;
309		_debug("new promise [fl=%lx]", vnode->flags);
310	}
311
312	/* check the permits to see if we've got one yet */
313	ret = afs_check_permit(vnode, key, &access);
314	if (ret < 0)
315		goto error;
316
317	/* interpret the access mask */
318	_debug("REQ %x ACC %x on %s",
319	       mask, access, S_ISDIR(inode->i_mode) ? "dir" : "file");
320
321	if (S_ISDIR(inode->i_mode)) {
322		if (mask & MAY_EXEC) {
323			if (!(access & AFS_ACE_LOOKUP))
324				goto permission_denied;
325		} else if (mask & MAY_READ) {
326			if (!(access & AFS_ACE_READ))
327				goto permission_denied;
328		} else if (mask & MAY_WRITE) {
329			if (!(access & (AFS_ACE_DELETE | /* rmdir, unlink, rename from */
330					AFS_ACE_INSERT | /* create, mkdir, symlink, rename to */
331					AFS_ACE_WRITE))) /* chmod */
332				goto permission_denied;
333		} else {
334			BUG();
335		}
336	} else {
337		if (!(access & AFS_ACE_LOOKUP))
338			goto permission_denied;
339		if (mask & (MAY_EXEC | MAY_READ)) {
340			if (!(access & AFS_ACE_READ))
341				goto permission_denied;
342		} else if (mask & MAY_WRITE) {
343			if (!(access & AFS_ACE_WRITE))
344				goto permission_denied;
345		}
346	}
347
348	key_put(key);
349	ret = generic_permission(inode, mask, NULL);
350	_leave(" = %d", ret);
351	return ret;
352
353permission_denied:
354	ret = -EACCES;
355error:
356	key_put(key);
357	_leave(" = %d", ret);
358	return ret;
359}
360