1 // SPDX-License-Identifier: GPL-2.0
3 * Verification of builtin signatures
5 * Copyright 2019 Google LLC
8 #include "fsverity_private.h"
10 #include <linux/cred.h>
11 #include <linux/key.h>
12 #include <linux/slab.h>
13 #include <linux/verification.h>
16 * /proc/sys/fs/verity/require_signatures
17 * If 1, all verity files must have a valid builtin signature.
19 static int fsverity_require_signatures;
22 * Keyring that contains the trusted X.509 certificates.
24 * Only root (kuid=0) can modify this. Also, root may use
25 * keyctl_restrict_keyring() to prevent any more additions.
27 static struct key *fsverity_keyring;
30 * fsverity_verify_signature() - check a verity file's signature
31 * @vi: the file's fsverity_info
32 * @desc: the file's fsverity_descriptor
33 * @desc_size: size of @desc
35 * If the file's fs-verity descriptor includes a signature of the file digest,
36 * verify it against the certificates in the fs-verity keyring.
38 * Return: 0 on success (signature valid or not required); -errno on failure
40 int fsverity_verify_signature(const struct fsverity_info *vi,
41 const struct fsverity_descriptor *desc,
44 const struct inode *inode = vi->inode;
45 const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg;
46 const u32 sig_size = le32_to_cpu(desc->sig_size);
47 struct fsverity_formatted_digest *d;
51 if (fsverity_require_signatures) {
53 "require_signatures=1, rejecting unsigned file!");
59 if (sig_size > desc_size - sizeof(*desc)) {
60 fsverity_err(inode, "Signature overflows verity descriptor");
64 d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL);
67 memcpy(d->magic, "FSVerity", 8);
68 d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs);
69 d->digest_size = cpu_to_le16(hash_alg->digest_size);
70 memcpy(d->digest, vi->file_digest, hash_alg->digest_size);
72 err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size,
73 desc->signature, sig_size,
75 VERIFYING_UNSPECIFIED_SIGNATURE,
82 "File's signing cert isn't in the fs-verity keyring");
83 else if (err == -EKEYREJECTED)
84 fsverity_err(inode, "Incorrect file signature");
85 else if (err == -EBADMSG)
86 fsverity_err(inode, "Malformed file signature");
88 fsverity_err(inode, "Error %d verifying file signature",
93 pr_debug("Valid signature for file digest %s:%*phN\n",
94 hash_alg->name, hash_alg->digest_size, vi->file_digest);
99 static struct ctl_table_header *fsverity_sysctl_header;
101 static const struct ctl_path fsverity_sysctl_path[] = {
102 { .procname = "fs", },
103 { .procname = "verity", },
107 static struct ctl_table fsverity_sysctl_table[] = {
109 .procname = "require_signatures",
110 .data = &fsverity_require_signatures,
111 .maxlen = sizeof(int),
113 .proc_handler = proc_dointvec_minmax,
114 .extra1 = SYSCTL_ZERO,
115 .extra2 = SYSCTL_ONE,
120 static int __init fsverity_sysctl_init(void)
122 fsverity_sysctl_header = register_sysctl_paths(fsverity_sysctl_path,
123 fsverity_sysctl_table);
124 if (!fsverity_sysctl_header) {
125 pr_err("sysctl registration failed!\n");
130 #else /* !CONFIG_SYSCTL */
131 static inline int __init fsverity_sysctl_init(void)
135 #endif /* !CONFIG_SYSCTL */
137 int __init fsverity_init_signature(void)
142 ring = keyring_alloc(".fs-verity", KUIDT_INIT(0), KGIDT_INIT(0),
143 current_cred(), KEY_POS_SEARCH |
144 KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE |
145 KEY_USR_SEARCH | KEY_USR_SETATTR,
146 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
148 return PTR_ERR(ring);
150 err = fsverity_sysctl_init();
154 fsverity_keyring = ring;