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  */
cachefiles_get_security_ID(struct cachefiles_cache * cache)20 int 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 			printk(KERN_ERR "CacheFiles:"
38 			       " Security denies permission to nominate"
39 			       " security context: error %d\n",
40 			       ret);
41 			goto error;
42 		}
43 	}
44 
45 	cache->cache_cred = new;
46 	ret = 0;
47 error:
48 	_leave(" = %d", ret);
49 	return ret;
50 }
51 
52 /*
53  * see if mkdir and create can be performed in the root directory
54  */
cachefiles_check_cache_dir(struct cachefiles_cache * cache,struct dentry * root)55 static int cachefiles_check_cache_dir(struct cachefiles_cache *cache,
56 				      struct dentry *root)
57 {
58 	int ret;
59 
60 	ret = security_inode_mkdir(root->d_inode, root, 0);
61 	if (ret < 0) {
62 		printk(KERN_ERR "CacheFiles:"
63 		       " Security denies permission to make dirs: error %d",
64 		       ret);
65 		return ret;
66 	}
67 
68 	ret = security_inode_create(root->d_inode, root, 0);
69 	if (ret < 0)
70 		printk(KERN_ERR "CacheFiles:"
71 		       " Security denies permission to create files: error %d",
72 		       ret);
73 
74 	return ret;
75 }
76 
77 /*
78  * check the security details of the on-disk cache
79  * - must be called with security override in force
80  * - must return with a security override in force - even in the case of an
81  *   error
82  */
cachefiles_determine_cache_security(struct cachefiles_cache * cache,struct dentry * root,const struct cred ** _saved_cred)83 int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
84 					struct dentry *root,
85 					const struct cred **_saved_cred)
86 {
87 	struct cred *new;
88 	int ret;
89 
90 	_enter("");
91 
92 	/* duplicate the cache creds for COW (the override is currently in
93 	 * force, so we can use prepare_creds() to do this) */
94 	new = prepare_creds();
95 	if (!new)
96 		return -ENOMEM;
97 
98 	cachefiles_end_secure(cache, *_saved_cred);
99 
100 	/* use the cache root dir's security context as the basis with
101 	 * which create files */
102 	ret = set_create_files_as(new, root->d_inode);
103 	if (ret < 0) {
104 		abort_creds(new);
105 		cachefiles_begin_secure(cache, _saved_cred);
106 		_leave(" = %d [cfa]", ret);
107 		return ret;
108 	}
109 
110 	put_cred(cache->cache_cred);
111 	cache->cache_cred = new;
112 
113 	cachefiles_begin_secure(cache, _saved_cred);
114 	ret = cachefiles_check_cache_dir(cache, root);
115 
116 	if (ret == -EOPNOTSUPP)
117 		ret = 0;
118 	_leave(" = %d", ret);
119 	return ret;
120 }
121