1// SPDX-License-Identifier: GPL-2.0-or-later
2/* Key permission checking
3 *
4 * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8#include <linux/export.h>
9#include <linux/security.h>
10#include "internal.h"
11
12/**
13 * key_task_permission - Check a key can be used
14 * @key_ref: The key to check.
15 * @cred: The credentials to use.
16 * @need_perm: The permission required.
17 *
18 * Check to see whether permission is granted to use a key in the desired way,
19 * but permit the security modules to override.
20 *
21 * The caller must hold either a ref on cred or must hold the RCU readlock.
22 *
23 * Returns 0 if successful, -EACCES if access is denied based on the
24 * permissions bits or the LSM check.
25 */
26int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
27 enum key_need_perm need_perm)
28{
29 struct key *key;
30 key_perm_t kperm, mask;
31 int ret;
32
33 switch (need_perm) {
34 default:
35 WARN_ON(1);
36 return -EACCES;
37 case KEY_NEED_UNLINK:
38 case KEY_SYSADMIN_OVERRIDE:
39 case KEY_AUTHTOKEN_OVERRIDE:
40 case KEY_DEFER_PERM_CHECK:
41 goto lsm;
42
43 case KEY_NEED_VIEW: mask = KEY_OTH_VIEW; break;
44 case KEY_NEED_READ: mask = KEY_OTH_READ; break;
45 case KEY_NEED_WRITE: mask = KEY_OTH_WRITE; break;
46 case KEY_NEED_SEARCH: mask = KEY_OTH_SEARCH; break;
47 case KEY_NEED_LINK: mask = KEY_OTH_LINK; break;
48 case KEY_NEED_SETATTR: mask = KEY_OTH_SETATTR; break;
49 }
50
51 key = key_ref_to_ptr(key_ref);
52
53 /* use the second 8-bits of permissions for keys the caller owns */
54 if (uid_eq(left: key->uid, right: cred->fsuid)) {
55 kperm = key->perm >> 16;
56 goto use_these_perms;
57 }
58
59 /* use the third 8-bits of permissions for keys the caller has a group
60 * membership in common with */
61 if (gid_valid(gid: key->gid) && key->perm & KEY_GRP_ALL) {
62 if (gid_eq(left: key->gid, right: cred->fsgid)) {
63 kperm = key->perm >> 8;
64 goto use_these_perms;
65 }
66
67 ret = groups_search(cred->group_info, key->gid);
68 if (ret) {
69 kperm = key->perm >> 8;
70 goto use_these_perms;
71 }
72 }
73
74 /* otherwise use the least-significant 8-bits */
75 kperm = key->perm;
76
77use_these_perms:
78
79 /* use the top 8-bits of permissions for keys the caller possesses
80 * - possessor permissions are additive with other permissions
81 */
82 if (is_key_possessed(key_ref))
83 kperm |= key->perm >> 24;
84
85 if ((kperm & mask) != mask)
86 return -EACCES;
87
88 /* let LSM be the final arbiter */
89lsm:
90 return security_key_permission(key_ref, cred, need_perm);
91}
92EXPORT_SYMBOL(key_task_permission);
93
94/**
95 * key_validate - Validate a key.
96 * @key: The key to be validated.
97 *
98 * Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
99 * key is invalidated, -EKEYREVOKED if the key's type has been removed or if
100 * the key has been revoked or -EKEYEXPIRED if the key has expired.
101 */
102int key_validate(const struct key *key)
103{
104 unsigned long flags = READ_ONCE(key->flags);
105 time64_t expiry = READ_ONCE(key->expiry);
106
107 if (flags & (1 << KEY_FLAG_INVALIDATED))
108 return -ENOKEY;
109
110 /* check it's still accessible */
111 if (flags & ((1 << KEY_FLAG_REVOKED) |
112 (1 << KEY_FLAG_DEAD)))
113 return -EKEYREVOKED;
114
115 /* check it hasn't expired */
116 if (expiry) {
117 if (ktime_get_real_seconds() >= expiry)
118 return -EKEYEXPIRED;
119 }
120
121 return 0;
122}
123EXPORT_SYMBOL(key_validate);
124