1/* CacheFiles security management
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 Licence
8 * as published by the Free Software Foundation; either version
9 * 2 of the Licence, or (at your option) any later version.
10 */
11
12#include <linux/fs.h>
13#include <linux/cred.h>
14#include "internal.h"
15
16/*
17 * determine the security context within which we access the cache from within
18 * the kernel
19 */
20int cachefiles_get_security_ID(struct cachefiles_cache *cache)
21{
22	struct cred *new;
23	int ret;
24
25	_enter("{%s}", cache->secctx);
26
27	new = prepare_kernel_cred(current);
28	if (!new) {
29		ret = -ENOMEM;
30		goto error;
31	}
32
33	if (cache->secctx) {
34		ret = set_security_override_from_ctx(new, cache->secctx);
35		if (ret < 0) {
36			put_cred(new);
37			pr_err("Security denies permission to nominate security context: error %d\n",
38			       ret);
39			goto error;
40		}
41	}
42
43	cache->cache_cred = new;
44	ret = 0;
45error:
46	_leave(" = %d", ret);
47	return ret;
48}
49
50/*
51 * see if mkdir and create can be performed in the root directory
52 */
53static int cachefiles_check_cache_dir(struct cachefiles_cache *cache,
54				      struct dentry *root)
55{
56	int ret;
57
58	ret = security_inode_mkdir(d_backing_inode(root), root, 0);
59	if (ret < 0) {
60		pr_err("Security denies permission to make dirs: error %d",
61		       ret);
62		return ret;
63	}
64
65	ret = security_inode_create(d_backing_inode(root), root, 0);
66	if (ret < 0)
67		pr_err("Security denies permission to create files: error %d",
68		       ret);
69
70	return ret;
71}
72
73/*
74 * check the security details of the on-disk cache
75 * - must be called with security override in force
76 * - must return with a security override in force - even in the case of an
77 *   error
78 */
79int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
80					struct dentry *root,
81					const struct cred **_saved_cred)
82{
83	struct cred *new;
84	int ret;
85
86	_enter("");
87
88	/* duplicate the cache creds for COW (the override is currently in
89	 * force, so we can use prepare_creds() to do this) */
90	new = prepare_creds();
91	if (!new)
92		return -ENOMEM;
93
94	cachefiles_end_secure(cache, *_saved_cred);
95
96	/* use the cache root dir's security context as the basis with
97	 * which create files */
98	ret = set_create_files_as(new, d_backing_inode(root));
99	if (ret < 0) {
100		abort_creds(new);
101		cachefiles_begin_secure(cache, _saved_cred);
102		_leave(" = %d [cfa]", ret);
103		return ret;
104	}
105
106	put_cred(cache->cache_cred);
107	cache->cache_cred = new;
108
109	cachefiles_begin_secure(cache, _saved_cred);
110	ret = cachefiles_check_cache_dir(cache, root);
111
112	if (ret == -EOPNOTSUPP)
113		ret = 0;
114	_leave(" = %d", ret);
115	return ret;
116}
117