1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Verification of builtin signatures
4 *
5 * Copyright 2019 Google LLC
6 */
7
8 #include "fsverity_private.h"
9
10 #include <linux/cred.h>
11 #include <linux/key.h>
12 #include <linux/slab.h>
13 #include <linux/verification.h>
14
15 /*
16 * /proc/sys/fs/verity/require_signatures
17 * If 1, all verity files must have a valid builtin signature.
18 */
19 static int fsverity_require_signatures;
20
21 /*
22 * Keyring that contains the trusted X.509 certificates.
23 *
24 * Only root (kuid=0) can modify this. Also, root may use
25 * keyctl_restrict_keyring() to prevent any more additions.
26 */
27 static struct key *fsverity_keyring;
28
29 /**
30 * fsverity_verify_signature() - check a verity file's signature
31 * @vi: the file's fsverity_info
32 * @signature: the file's built-in signature
33 * @sig_size: size of signature in bytes, or 0 if no signature
34 *
35 * If the file includes a signature of its fs-verity file digest, verify it
36 * against the certificates in the fs-verity keyring.
37 *
38 * Return: 0 on success (signature valid or not required); -errno on failure
39 */
fsverity_verify_signature(const struct fsverity_info * vi,const u8 * signature,size_t sig_size)40 int fsverity_verify_signature(const struct fsverity_info *vi,
41 const u8 *signature, size_t sig_size)
42 {
43 unsigned int digest_algorithm =
44 vi->tree_params.hash_alg - fsverity_hash_algs;
45
46 return __fsverity_verify_signature(vi->inode, signature, sig_size,
47 vi->file_digest, digest_algorithm);
48 }
49
50 /**
51 * __fsverity_verify_signature() - check a verity file's signature
52 * @inode: the file's inode
53 * @signature: the file's signature
54 * @sig_size: size of @signature. Can be 0 if there is no signature
55 * @file_digest: the file's digest
56 * @digest_algorithm: the digest algorithm used
57 *
58 * Takes the file's digest and optional signature and verifies the signature
59 * against the digest and the fs-verity keyring if appropriate
60 *
61 * Return: 0 on success (signature valid or not required); -errno on failure
62 */
__fsverity_verify_signature(const struct inode * inode,const u8 * signature,size_t sig_size,const u8 * file_digest,unsigned int digest_algorithm)63 int __fsverity_verify_signature(const struct inode *inode, const u8 *signature,
64 size_t sig_size, const u8 *file_digest,
65 unsigned int digest_algorithm)
66 {
67 struct fsverity_formatted_digest *d;
68 struct fsverity_hash_alg *hash_alg = fsverity_get_hash_alg(inode,
69 digest_algorithm);
70 int err;
71
72 if (IS_ERR(hash_alg))
73 return PTR_ERR(hash_alg);
74
75 if (sig_size == 0) {
76 if (fsverity_require_signatures) {
77 fsverity_err(inode,
78 "require_signatures=1, rejecting unsigned file!");
79 return -EPERM;
80 }
81 return 0;
82 }
83
84 d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL);
85 if (!d)
86 return -ENOMEM;
87 memcpy(d->magic, "FSVerity", 8);
88 d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs);
89 d->digest_size = cpu_to_le16(hash_alg->digest_size);
90 memcpy(d->digest, file_digest, hash_alg->digest_size);
91
92 err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size,
93 signature, sig_size, fsverity_keyring,
94 VERIFYING_UNSPECIFIED_SIGNATURE,
95 NULL, NULL);
96 kfree(d);
97
98 if (err) {
99 if (err == -ENOKEY)
100 fsverity_err(inode,
101 "File's signing cert isn't in the fs-verity keyring");
102 else if (err == -EKEYREJECTED)
103 fsverity_err(inode, "Incorrect file signature");
104 else if (err == -EBADMSG)
105 fsverity_err(inode, "Malformed file signature");
106 else
107 fsverity_err(inode, "Error %d verifying file signature",
108 err);
109 return err;
110 }
111
112 pr_debug("Valid signature for file digest %s:%*phN\n",
113 hash_alg->name, hash_alg->digest_size, file_digest);
114 return 0;
115 }
116 EXPORT_SYMBOL_GPL(__fsverity_verify_signature);
117
118 #ifdef CONFIG_SYSCTL
119 static struct ctl_table_header *fsverity_sysctl_header;
120
121 static const struct ctl_path fsverity_sysctl_path[] = {
122 { .procname = "fs", },
123 { .procname = "verity", },
124 { }
125 };
126
127 static struct ctl_table fsverity_sysctl_table[] = {
128 {
129 .procname = "require_signatures",
130 .data = &fsverity_require_signatures,
131 .maxlen = sizeof(int),
132 .mode = 0644,
133 .proc_handler = proc_dointvec_minmax,
134 .extra1 = SYSCTL_ZERO,
135 .extra2 = SYSCTL_ONE,
136 },
137 { }
138 };
139
fsverity_sysctl_init(void)140 static int __init fsverity_sysctl_init(void)
141 {
142 fsverity_sysctl_header = register_sysctl_paths(fsverity_sysctl_path,
143 fsverity_sysctl_table);
144 if (!fsverity_sysctl_header) {
145 pr_err("sysctl registration failed!\n");
146 return -ENOMEM;
147 }
148 return 0;
149 }
150 #else /* !CONFIG_SYSCTL */
fsverity_sysctl_init(void)151 static inline int __init fsverity_sysctl_init(void)
152 {
153 return 0;
154 }
155 #endif /* !CONFIG_SYSCTL */
156
fsverity_init_signature(void)157 int __init fsverity_init_signature(void)
158 {
159 struct key *ring;
160 int err;
161
162 ring = keyring_alloc(".fs-verity", KUIDT_INIT(0), KGIDT_INIT(0),
163 current_cred(), KEY_POS_SEARCH |
164 KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE |
165 KEY_USR_SEARCH | KEY_USR_SETATTR,
166 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
167 if (IS_ERR(ring))
168 return PTR_ERR(ring);
169
170 err = fsverity_sysctl_init();
171 if (err)
172 goto err_put_ring;
173
174 fsverity_keyring = ring;
175 return 0;
176
177 err_put_ring:
178 key_put(ring);
179 return err;
180 }
181