xref: /linux/security/keys/permission.c (revision 4b4193256c8d3bc3a5397b5cd9494c2ad386317d)
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  */
key_task_permission(const key_ref_t key_ref,const struct cred * cred,enum key_need_perm need_perm)26 int 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(key->uid, 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(key->gid) && key->perm & KEY_GRP_ALL) {
62 		if (gid_eq(key->gid, 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 
77 use_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 */
89 lsm:
90 	return security_key_permission(key_ref, cred, need_perm);
91 }
92 EXPORT_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  */
key_validate(const struct key * key)102 int 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 }
123 EXPORT_SYMBOL(key_validate);
124