xref: /openbmc/linux/security/keys/permission.c (revision b34e08d5)
1 /* Key permission checking
2  *
3  * Copyright (C) 2005 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/module.h>
13 #include <linux/security.h>
14 #include "internal.h"
15 
16 /**
17  * key_task_permission - Check a key can be used
18  * @key_ref: The key to check.
19  * @cred: The credentials to use.
20  * @perm: The permissions to check for.
21  *
22  * Check to see whether permission is granted to use a key in the desired way,
23  * but permit the security modules to override.
24  *
25  * The caller must hold either a ref on cred or must hold the RCU readlock.
26  *
27  * Returns 0 if successful, -EACCES if access is denied based on the
28  * permissions bits or the LSM check.
29  */
30 int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
31 			key_perm_t perm)
32 {
33 	struct key *key;
34 	key_perm_t kperm;
35 	int ret;
36 
37 	key = key_ref_to_ptr(key_ref);
38 
39 	/* use the second 8-bits of permissions for keys the caller owns */
40 	if (uid_eq(key->uid, cred->fsuid)) {
41 		kperm = key->perm >> 16;
42 		goto use_these_perms;
43 	}
44 
45 	/* use the third 8-bits of permissions for keys the caller has a group
46 	 * membership in common with */
47 	if (gid_valid(key->gid) && key->perm & KEY_GRP_ALL) {
48 		if (gid_eq(key->gid, cred->fsgid)) {
49 			kperm = key->perm >> 8;
50 			goto use_these_perms;
51 		}
52 
53 		ret = groups_search(cred->group_info, key->gid);
54 		if (ret) {
55 			kperm = key->perm >> 8;
56 			goto use_these_perms;
57 		}
58 	}
59 
60 	/* otherwise use the least-significant 8-bits */
61 	kperm = key->perm;
62 
63 use_these_perms:
64 
65 	/* use the top 8-bits of permissions for keys the caller possesses
66 	 * - possessor permissions are additive with other permissions
67 	 */
68 	if (is_key_possessed(key_ref))
69 		kperm |= key->perm >> 24;
70 
71 	kperm = kperm & perm & KEY_ALL;
72 
73 	if (kperm != perm)
74 		return -EACCES;
75 
76 	/* let LSM be the final arbiter */
77 	return security_key_permission(key_ref, cred, perm);
78 }
79 EXPORT_SYMBOL(key_task_permission);
80 
81 /**
82  * key_validate - Validate a key.
83  * @key: The key to be validated.
84  *
85  * Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
86  * key is invalidated, -EKEYREVOKED if the key's type has been removed or if
87  * the key has been revoked or -EKEYEXPIRED if the key has expired.
88  */
89 int key_validate(const struct key *key)
90 {
91 	unsigned long flags = key->flags;
92 
93 	if (flags & (1 << KEY_FLAG_INVALIDATED))
94 		return -ENOKEY;
95 
96 	/* check it's still accessible */
97 	if (flags & ((1 << KEY_FLAG_REVOKED) |
98 		     (1 << KEY_FLAG_DEAD)))
99 		return -EKEYREVOKED;
100 
101 	/* check it hasn't expired */
102 	if (key->expiry) {
103 		struct timespec now = current_kernel_time();
104 		if (now.tv_sec >= key->expiry)
105 			return -EKEYEXPIRED;
106 	}
107 
108 	return 0;
109 }
110 EXPORT_SYMBOL(key_validate);
111