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(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
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