1/*
2 * Copyright (C) 2011 Nokia Corporation
3 * Copyright (C) 2011 Intel Corporation
4 *
5 * Author:
6 * Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
7 * <dmitry.kasatkin@intel.com>
8 *
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License as published by
11 * the Free Software Foundation, version 2 of the License.
12 *
13 * File: sign.c
14 * implements signature (RSA) verification
15 * pkcs decoding is based on LibTomCrypt code
16 */
17
18#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
19
20#include <linux/err.h>
21#include <linux/module.h>
22#include <linux/slab.h>
23#include <linux/key.h>
24#include <linux/crypto.h>
25#include <crypto/hash.h>
26#include <crypto/sha.h>
27#include <keys/user-type.h>
28#include <linux/mpi.h>
29#include <linux/digsig.h>
30
31static struct crypto_shash *shash;
32
33static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
34 unsigned long msglen,
35 unsigned long modulus_bitlen,
36 unsigned long *outlen)
37{
38 unsigned long modulus_len, ps_len, i;
39
40 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
41
42 /* test message size */
43 if ((msglen > modulus_len) || (modulus_len < 11))
44 return NULL;
45
46 /* separate encoded message */
47 if (msg[0] != 0x00 || msg[1] != 0x01)
48 return NULL;
49
50 for (i = 2; i < modulus_len - 1; i++)
51 if (msg[i] != 0xFF)
52 break;
53
54 /* separator check */
55 if (msg[i] != 0)
56 /* There was no octet with hexadecimal value 0x00
57 to separate ps from m. */
58 return NULL;
59
60 ps_len = i - 2;
61
62 *outlen = (msglen - (2 + ps_len + 1));
63
64 return msg + 2 + ps_len + 1;
65}
66
67/*
68 * RSA Signature verification with public key
69 */
70static int digsig_verify_rsa(struct key *key,
71 const char *sig, int siglen,
72 const char *h, int hlen)
73{
74 int err = -EINVAL;
75 unsigned long len;
76 unsigned long mlen, mblen;
77 unsigned nret, l;
78 int head, i;
79 unsigned char *out1 = NULL;
80 const char *m;
81 MPI in = NULL, res = NULL, pkey[2];
82 uint8_t *p, *datap;
83 const uint8_t *endp;
84 const struct user_key_payload *ukp;
85 struct pubkey_hdr *pkh;
86
87 down_read(&key->sem);
88 ukp = user_key_payload_locked(key);
89
90 if (!ukp) {
91 /* key was revoked before we acquired its semaphore */
92 err = -EKEYREVOKED;
93 goto err1;
94 }
95
96 if (ukp->datalen < sizeof(*pkh))
97 goto err1;
98
99 pkh = (struct pubkey_hdr *)ukp->data;
100
101 if (pkh->version != 1)
102 goto err1;
103
104 if (pkh->algo != PUBKEY_ALGO_RSA)
105 goto err1;
106
107 if (pkh->nmpi != 2)
108 goto err1;
109
110 datap = pkh->mpi;
111 endp = ukp->data + ukp->datalen;
112
113 for (i = 0; i < pkh->nmpi; i++) {
114 unsigned int remaining = endp - datap;
115 pkey[i] = mpi_read_from_buffer(datap, &remaining);
116 if (IS_ERR(pkey[i])) {
117 err = PTR_ERR(pkey[i]);
118 goto err;
119 }
120 datap += remaining;
121 }
122
123 mblen = mpi_get_nbits(pkey[0]);
124 mlen = DIV_ROUND_UP(mblen, 8);
125
126 if (mlen == 0) {
127 err = -EINVAL;
128 goto err;
129 }
130
131 err = -ENOMEM;
132
133 out1 = kzalloc(mlen, GFP_KERNEL);
134 if (!out1)
135 goto err;
136
137 nret = siglen;
138 in = mpi_read_from_buffer(sig, &nret);
139 if (IS_ERR(in)) {
140 err = PTR_ERR(in);
141 goto err;
142 }
143
144 res = mpi_alloc(mpi_get_nlimbs(in) * 2);
145 if (!res)
146 goto err;
147
148 err = mpi_powm(res, in, pkey[1], pkey[0]);
149 if (err)
150 goto err;
151
152 if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
153 err = -EINVAL;
154 goto err;
155 }
156
157 p = mpi_get_buffer(res, &l, NULL);
158 if (!p) {
159 err = -EINVAL;
160 goto err;
161 }
162
163 len = mlen;
164 head = len - l;
165 memset(out1, 0, head);
166 memcpy(out1 + head, p, l);
167
168 kfree(p);
169
170 m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
171
172 if (!m || len != hlen || memcmp(m, h, hlen))
173 err = -EINVAL;
174
175err:
176 mpi_free(in);
177 mpi_free(res);
178 kfree(out1);
179 while (--i >= 0)
180 mpi_free(pkey[i]);
181err1:
182 up_read(&key->sem);
183
184 return err;
185}
186
187/**
188 * digsig_verify() - digital signature verification with public key
189 * @keyring: keyring to search key in
190 * @sig: digital signature
191 * @siglen: length of the signature
192 * @data: data
193 * @datalen: length of the data
194 *
195 * Returns 0 on success, -EINVAL otherwise
196 *
197 * Verifies data integrity against digital signature.
198 * Currently only RSA is supported.
199 * Normally hash of the content is used as a data for this function.
200 *
201 */
202int digsig_verify(struct key *keyring, const char *sig, int siglen,
203 const char *data, int datalen)
204{
205 int err = -ENOMEM;
206 struct signature_hdr *sh = (struct signature_hdr *)sig;
207 struct shash_desc *desc = NULL;
208 unsigned char hash[SHA1_DIGEST_SIZE];
209 struct key *key;
210 char name[20];
211
212 if (siglen < sizeof(*sh) + 2)
213 return -EINVAL;
214
215 if (sh->algo != PUBKEY_ALGO_RSA)
216 return -ENOTSUPP;
217
218 sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
219
220 if (keyring) {
221 /* search in specific keyring */
222 key_ref_t kref;
223 kref = keyring_search(make_key_ref(keyring, 1UL),
224 &key_type_user, name);
225 if (IS_ERR(kref))
226 key = ERR_CAST(kref);
227 else
228 key = key_ref_to_ptr(kref);
229 } else {
230 key = request_key(&key_type_user, name, NULL);
231 }
232 if (IS_ERR(key)) {
233 pr_err("key not found, id: %s\n", name);
234 return PTR_ERR(key);
235 }
236
237 desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
238 GFP_KERNEL);
239 if (!desc)
240 goto err;
241
242 desc->tfm = shash;
243 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
244
245 crypto_shash_init(desc);
246 crypto_shash_update(desc, data, datalen);
247 crypto_shash_update(desc, sig, sizeof(*sh));
248 crypto_shash_final(desc, hash);
249
250 kfree(desc);
251
252 /* pass signature mpis address */
253 err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
254 hash, sizeof(hash));
255
256err:
257 key_put(key);
258
259 return err ? -EINVAL : 0;
260}
261EXPORT_SYMBOL_GPL(digsig_verify);
262
263static int __init digsig_init(void)
264{
265 shash = crypto_alloc_shash("sha1", 0, 0);
266 if (IS_ERR(shash)) {
267 pr_err("shash allocation failed\n");
268 return PTR_ERR(shash);
269 }
270
271 return 0;
272
273}
274
275static void __exit digsig_cleanup(void)
276{
277 crypto_free_shash(shash);
278}
279
280module_init(digsig_init);
281module_exit(digsig_cleanup);
282
283MODULE_LICENSE("GPL");
284