1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (C) 2011 Nokia Corporation
4 * Copyright (C) 2011 Intel Corporation
5 *
6 * Author:
7 * Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
8 * <dmitry.kasatkin@intel.com>
9 *
10 * File: sign.c
11 * implements signature (RSA) verification
12 * pkcs decoding is based on LibTomCrypt code
13 */
14
15 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
16
17 #include <linux/err.h>
18 #include <linux/module.h>
19 #include <linux/slab.h>
20 #include <linux/key.h>
21 #include <linux/crypto.h>
22 #include <crypto/hash.h>
23 #include <crypto/sha1.h>
24 #include <keys/user-type.h>
25 #include <linux/mpi.h>
26 #include <linux/digsig.h>
27
28 static struct crypto_shash *shash;
29
30 static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
31 unsigned long msglen,
32 unsigned long modulus_bitlen,
33 unsigned long *outlen)
34 {
35 unsigned long modulus_len, ps_len, i;
36
37 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
38
39 /* test message size */
40 if ((msglen > modulus_len) || (modulus_len < 11))
41 return NULL;
42
43 /* separate encoded message */
44 if (msg[0] != 0x00 || msg[1] != 0x01)
45 return NULL;
46
47 for (i = 2; i < modulus_len - 1; i++)
48 if (msg[i] != 0xFF)
49 break;
50
51 /* separator check */
52 if (msg[i] != 0)
53 /* There was no octet with hexadecimal value 0x00
54 to separate ps from m. */
55 return NULL;
56
57 ps_len = i - 2;
58
59 *outlen = (msglen - (2 + ps_len + 1));
60
61 return msg + 2 + ps_len + 1;
62 }
63
64 /*
65 * RSA Signature verification with public key
66 */
67 static int digsig_verify_rsa(struct key *key,
68 const char *sig, int siglen,
69 const char *h, int hlen)
70 {
71 int err = -EINVAL;
72 unsigned long len;
73 unsigned long mlen, mblen;
74 unsigned nret, l;
75 int head, i;
76 unsigned char *out1 = NULL;
77 const char *m;
78 MPI in = NULL, res = NULL, pkey[2];
79 uint8_t *p, *datap;
80 const uint8_t *endp;
81 const struct user_key_payload *ukp;
82 struct pubkey_hdr *pkh;
83
84 down_read(&key->sem);
85 ukp = user_key_payload_locked(key);
86
87 if (!ukp) {
88 /* key was revoked before we acquired its semaphore */
89 err = -EKEYREVOKED;
90 goto err1;
91 }
92
93 if (ukp->datalen < sizeof(*pkh))
94 goto err1;
95
96 pkh = (struct pubkey_hdr *)ukp->data;
97
98 if (pkh->version != 1)
99 goto err1;
100
101 if (pkh->algo != PUBKEY_ALGO_RSA)
102 goto err1;
103
104 if (pkh->nmpi != 2)
105 goto err1;
106
107 datap = pkh->mpi;
108 endp = ukp->data + ukp->datalen;
109
110 for (i = 0; i < pkh->nmpi; i++) {
111 unsigned int remaining = endp - datap;
112 pkey[i] = mpi_read_from_buffer(datap, &remaining);
113 if (IS_ERR(pkey[i])) {
114 err = PTR_ERR(pkey[i]);
115 goto err;
116 }
117 datap += remaining;
118 }
119
120 mblen = mpi_get_nbits(pkey[0]);
121 mlen = DIV_ROUND_UP(mblen, 8);
122
123 if (mlen == 0) {
124 err = -EINVAL;
125 goto err;
126 }
127
128 err = -ENOMEM;
129
130 out1 = kzalloc(mlen, GFP_KERNEL);
131 if (!out1)
132 goto err;
133
134 nret = siglen;
135 in = mpi_read_from_buffer(sig, &nret);
136 if (IS_ERR(in)) {
137 err = PTR_ERR(in);
138 goto err;
139 }
140
141 res = mpi_alloc(mpi_get_nlimbs(in) * 2);
142 if (!res)
143 goto err;
144
145 err = mpi_powm(res, in, pkey[1], pkey[0]);
146 if (err)
147 goto err;
148
149 if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
150 err = -EINVAL;
151 goto err;
152 }
153
154 p = mpi_get_buffer(res, &l, NULL);
155 if (!p) {
156 err = -EINVAL;
157 goto err;
158 }
159
160 len = mlen;
161 head = len - l;
162 memset(out1, 0, head);
163 memcpy(out1 + head, p, l);
164
165 kfree(p);
166
167 m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
168
169 if (!m || len != hlen || memcmp(m, h, hlen))
170 err = -EINVAL;
171
172 err:
173 mpi_free(in);
174 mpi_free(res);
175 kfree(out1);
176 while (--i >= 0)
177 mpi_free(pkey[i]);
178 err1:
179 up_read(&key->sem);
180
181 return err;
182 }
183
184 /**
185 * digsig_verify() - digital signature verification with public key
186 * @keyring: keyring to search key in
187 * @sig: digital signature
188 * @siglen: length of the signature
189 * @data: data
190 * @datalen: length of the data
191 *
192 * Returns 0 on success, -EINVAL otherwise
193 *
194 * Verifies data integrity against digital signature.
195 * Currently only RSA is supported.
196 * Normally hash of the content is used as a data for this function.
197 *
198 */
199 int digsig_verify(struct key *keyring, const char *sig, int siglen,
200 const char *data, int datalen)
201 {
202 int err = -ENOMEM;
203 struct signature_hdr *sh = (struct signature_hdr *)sig;
204 struct shash_desc *desc = NULL;
205 unsigned char hash[SHA1_DIGEST_SIZE];
206 struct key *key;
207 char name[20];
208
209 if (siglen < sizeof(*sh) + 2)
210 return -EINVAL;
211
212 if (sh->algo != PUBKEY_ALGO_RSA)
213 return -ENOTSUPP;
214
215 sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
216
217 if (keyring) {
218 /* search in specific keyring */
219 key_ref_t kref;
220 kref = keyring_search(make_key_ref(keyring, 1UL),
221 &key_type_user, name, true);
222 if (IS_ERR(kref))
223 key = ERR_CAST(kref);
224 else
225 key = key_ref_to_ptr(kref);
226 } else {
227 key = request_key(&key_type_user, name, NULL);
228 }
229 if (IS_ERR(key)) {
230 pr_err("key not found, id: %s\n", name);
231 return PTR_ERR(key);
232 }
233
234 desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
235 GFP_KERNEL);
236 if (!desc)
237 goto err;
238
239 desc->tfm = shash;
240
241 crypto_shash_init(desc);
242 crypto_shash_update(desc, data, datalen);
243 crypto_shash_update(desc, sig, sizeof(*sh));
244 crypto_shash_final(desc, hash);
245
246 kfree(desc);
247
248 /* pass signature mpis address */
249 err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
250 hash, sizeof(hash));
251
252 err:
253 key_put(key);
254
255 return err ? -EINVAL : 0;
256 }
257 EXPORT_SYMBOL_GPL(digsig_verify);
258
259 static int __init digsig_init(void)
260 {
261 shash = crypto_alloc_shash("sha1", 0, 0);
262 if (IS_ERR(shash)) {
263 pr_err("shash allocation failed\n");
264 return PTR_ERR(shash);
265 }
266
267 return 0;
268
269 }
270
271 static void __exit digsig_cleanup(void)
272 {
273 crypto_free_shash(shash);
274 }
275
276 module_init(digsig_init);
277 module_exit(digsig_cleanup);
278
279 MODULE_LICENSE("GPL");
280
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.