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
31 static struct crypto_shash *shash;
32
pkcs_1_v1_5_decode_emsa(const unsigned char * msg,unsigned long msglen,unsigned long modulus_bitlen,unsigned long * outlen)33 static 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 */
digsig_verify_rsa(struct key * key,const char * sig,int siglen,const char * h,int hlen)70 static 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(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91 /* key was revoked before we acquired its semaphore */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 err = -ENOMEM;
114
115 for (i = 0; i < pkh->nmpi; i++) {
116 unsigned int remaining = endp - datap;
117 pkey[i] = mpi_read_from_buffer(datap, &remaining);
118 if (!pkey[i])
119 goto err;
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 goto err;
128
129 out1 = kzalloc(mlen, GFP_KERNEL);
130 if (!out1)
131 goto err;
132
133 nret = siglen;
134 in = mpi_read_from_buffer(sig, &nret);
135 if (!in)
136 goto err;
137
138 res = mpi_alloc(mpi_get_nlimbs(in) * 2);
139 if (!res)
140 goto err;
141
142 err = mpi_powm(res, in, pkey[1], pkey[0]);
143 if (err)
144 goto err;
145
146 if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
147 err = -EINVAL;
148 goto err;
149 }
150
151 p = mpi_get_buffer(res, &l, NULL);
152 if (!p) {
153 err = -EINVAL;
154 goto err;
155 }
156
157 len = mlen;
158 head = len - l;
159 memset(out1, 0, head);
160 memcpy(out1 + head, p, l);
161
162 kfree(p);
163
164 m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
165
166 if (!m || len != hlen || memcmp(m, h, hlen))
167 err = -EINVAL;
168
169 err:
170 mpi_free(in);
171 mpi_free(res);
172 kfree(out1);
173 while (--i >= 0)
174 mpi_free(pkey[i]);
175 err1:
176 up_read(&key->sem);
177
178 return err;
179 }
180
181 /**
182 * digsig_verify() - digital signature verification with public key
183 * @keyring: keyring to search key in
184 * @sig: digital signature
185 * @siglen: length of the signature
186 * @data: data
187 * @datalen: length of the data
188 *
189 * Returns 0 on success, -EINVAL otherwise
190 *
191 * Verifies data integrity against digital signature.
192 * Currently only RSA is supported.
193 * Normally hash of the content is used as a data for this function.
194 *
195 */
digsig_verify(struct key * keyring,const char * sig,int siglen,const char * data,int datalen)196 int digsig_verify(struct key *keyring, const char *sig, int siglen,
197 const char *data, int datalen)
198 {
199 int err = -ENOMEM;
200 struct signature_hdr *sh = (struct signature_hdr *)sig;
201 struct shash_desc *desc = NULL;
202 unsigned char hash[SHA1_DIGEST_SIZE];
203 struct key *key;
204 char name[20];
205
206 if (siglen < sizeof(*sh) + 2)
207 return -EINVAL;
208
209 if (sh->algo != PUBKEY_ALGO_RSA)
210 return -ENOTSUPP;
211
212 sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
213
214 if (keyring) {
215 /* search in specific keyring */
216 key_ref_t kref;
217 kref = keyring_search(make_key_ref(keyring, 1UL),
218 &key_type_user, name);
219 if (IS_ERR(kref))
220 key = ERR_CAST(kref);
221 else
222 key = key_ref_to_ptr(kref);
223 } else {
224 key = request_key(&key_type_user, name, NULL);
225 }
226 if (IS_ERR(key)) {
227 pr_err("key not found, id: %s\n", name);
228 return PTR_ERR(key);
229 }
230
231 desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
232 GFP_KERNEL);
233 if (!desc)
234 goto err;
235
236 desc->tfm = shash;
237 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
238
239 crypto_shash_init(desc);
240 crypto_shash_update(desc, data, datalen);
241 crypto_shash_update(desc, sig, sizeof(*sh));
242 crypto_shash_final(desc, hash);
243
244 kfree(desc);
245
246 /* pass signature mpis address */
247 err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
248 hash, sizeof(hash));
249
250 err:
251 key_put(key);
252
253 return err ? -EINVAL : 0;
254 }
255 EXPORT_SYMBOL_GPL(digsig_verify);
256
digsig_init(void)257 static int __init digsig_init(void)
258 {
259 shash = crypto_alloc_shash("sha1", 0, 0);
260 if (IS_ERR(shash)) {
261 pr_err("shash allocation failed\n");
262 return PTR_ERR(shash);
263 }
264
265 return 0;
266
267 }
268
digsig_cleanup(void)269 static void __exit digsig_cleanup(void)
270 {
271 crypto_free_shash(shash);
272 }
273
274 module_init(digsig_init);
275 module_exit(digsig_cleanup);
276
277 MODULE_LICENSE("GPL");
278