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Linux kernel mirror (for testing)
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linux
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * fs/verity/signature.c: 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 */
19static 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 */
27static struct key *fsverity_keyring;
28
29/**
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
34 *
35 * If the file's fs-verity descriptor includes a signature of the file
36 * measurement, verify it against the certificates in the fs-verity keyring.
37 *
38 * Return: 0 on success (signature valid or not required); -errno on failure
39 */
40int fsverity_verify_signature(const struct fsverity_info *vi,
41 const struct fsverity_descriptor *desc,
42 size_t desc_size)
43{
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_signed_digest *d;
48 int err;
49
50 if (sig_size == 0) {
51 if (fsverity_require_signatures) {
52 fsverity_err(inode,
53 "require_signatures=1, rejecting unsigned file!");
54 return -EPERM;
55 }
56 return 0;
57 }
58
59 if (sig_size > desc_size - sizeof(*desc)) {
60 fsverity_err(inode, "Signature overflows verity descriptor");
61 return -EBADMSG;
62 }
63
64 d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL);
65 if (!d)
66 return -ENOMEM;
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->measurement, hash_alg->digest_size);
71
72 err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size,
73 desc->signature, sig_size,
74 fsverity_keyring,
75 VERIFYING_UNSPECIFIED_SIGNATURE,
76 NULL, NULL);
77 kfree(d);
78
79 if (err) {
80 if (err == -ENOKEY)
81 fsverity_err(inode,
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");
87 else
88 fsverity_err(inode, "Error %d verifying file signature",
89 err);
90 return err;
91 }
92
93 pr_debug("Valid signature for file measurement %s:%*phN\n",
94 hash_alg->name, hash_alg->digest_size, vi->measurement);
95 return 0;
96}
97
98#ifdef CONFIG_SYSCTL
99static struct ctl_table_header *fsverity_sysctl_header;
100
101static const struct ctl_path fsverity_sysctl_path[] = {
102 { .procname = "fs", },
103 { .procname = "verity", },
104 { }
105};
106
107static struct ctl_table fsverity_sysctl_table[] = {
108 {
109 .procname = "require_signatures",
110 .data = &fsverity_require_signatures,
111 .maxlen = sizeof(int),
112 .mode = 0644,
113 .proc_handler = proc_dointvec_minmax,
114 .extra1 = SYSCTL_ZERO,
115 .extra2 = SYSCTL_ONE,
116 },
117 { }
118};
119
120static int __init fsverity_sysctl_init(void)
121{
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");
126 return -ENOMEM;
127 }
128 return 0;
129}
130#else /* !CONFIG_SYSCTL */
131static inline int __init fsverity_sysctl_init(void)
132{
133 return 0;
134}
135#endif /* !CONFIG_SYSCTL */
136
137int __init fsverity_init_signature(void)
138{
139 struct key *ring;
140 int err;
141
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);
147 if (IS_ERR(ring))
148 return PTR_ERR(ring);
149
150 err = fsverity_sysctl_init();
151 if (err)
152 goto err_put_ring;
153
154 fsverity_keyring = ring;
155 return 0;
156
157err_put_ring:
158 key_put(ring);
159 return err;
160}