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, *endp;
83 struct user_key_payload *ukp;
84 struct pubkey_hdr *pkh;
85
86 down_read(&key->sem);
87 ukp = key->payload.data;
88
89 if (!ukp) {
90 /* key was revoked before we acquired its semaphore */
91 err = -EKEYREVOKED;
92 goto err1;
93 }
94
95 if (ukp->datalen < sizeof(*pkh))
96 goto err1;
97
98 pkh = (struct pubkey_hdr *)ukp->data;
99
100 if (pkh->version != 1)
101 goto err1;
102
103 if (pkh->algo != PUBKEY_ALGO_RSA)
104 goto err1;
105
106 if (pkh->nmpi != 2)
107 goto err1;
108
109 datap = pkh->mpi;
110 endp = ukp->data + ukp->datalen;
111
112 err = -ENOMEM;
113
114 for (i = 0; i < pkh->nmpi; i++) {
115 unsigned int remaining = endp - datap;
116 pkey[i] = mpi_read_from_buffer(datap, &remaining);
117 if (!pkey[i])
118 goto err;
119 datap += remaining;
120 }
121
122 mblen = mpi_get_nbits(pkey[0]);
123 mlen = DIV_ROUND_UP(mblen, 8);
124
125 if (mlen == 0)
126 goto err;
127
128 out1 = kzalloc(mlen, GFP_KERNEL);
129 if (!out1)
130 goto err;
131
132 nret = siglen;
133 in = mpi_read_from_buffer(sig, &nret);
134 if (!in)
135 goto err;
136
137 res = mpi_alloc(mpi_get_nlimbs(in) * 2);
138 if (!res)
139 goto err;
140
141 err = mpi_powm(res, in, pkey[1], pkey[0]);
142 if (err)
143 goto err;
144
145 if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
146 err = -EINVAL;
147 goto err;
148 }
149
150 p = mpi_get_buffer(res, &l, NULL);
151 if (!p) {
152 err = -EINVAL;
153 goto err;
154 }
155
156 len = mlen;
157 head = len - l;
158 memset(out1, 0, head);
159 memcpy(out1 + head, p, l);
160
161 kfree(p);
162
163 m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
164
165 if (!m || len != hlen || memcmp(m, h, hlen))
166 err = -EINVAL;
167
168 err:
169 mpi_free(in);
170 mpi_free(res);
171 kfree(out1);
172 while (--i >= 0)
173 mpi_free(pkey[i]);
174 err1:
175 up_read(&key->sem);
176
177 return err;
178 }
179
180 /**
181 * digsig_verify() - digital signature verification with public key
182 * @keyring: keyring to search key in
183 * @sig: digital signature
184 * @siglen: length of the signature
185 * @data: data
186 * @datalen: length of the data
187 *
188 * Returns 0 on success, -EINVAL otherwise
189 *
190 * Verifies data integrity against digital signature.
191 * Currently only RSA is supported.
192 * Normally hash of the content is used as a data for this function.
193 *
194 */
digsig_verify(struct key * keyring,const char * sig,int siglen,const char * data,int datalen)195 int digsig_verify(struct key *keyring, const char *sig, int siglen,
196 const char *data, int datalen)
197 {
198 int err = -ENOMEM;
199 struct signature_hdr *sh = (struct signature_hdr *)sig;
200 struct shash_desc *desc = NULL;
201 unsigned char hash[SHA1_DIGEST_SIZE];
202 struct key *key;
203 char name[20];
204
205 if (siglen < sizeof(*sh) + 2)
206 return -EINVAL;
207
208 if (sh->algo != PUBKEY_ALGO_RSA)
209 return -ENOTSUPP;
210
211 sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
212
213 if (keyring) {
214 /* search in specific keyring */
215 key_ref_t kref;
216 kref = keyring_search(make_key_ref(keyring, 1UL),
217 &key_type_user, name);
218 if (IS_ERR(kref))
219 key = ERR_CAST(kref);
220 else
221 key = key_ref_to_ptr(kref);
222 } else {
223 key = request_key(&key_type_user, name, NULL);
224 }
225 if (IS_ERR(key)) {
226 pr_err("key not found, id: %s\n", name);
227 return PTR_ERR(key);
228 }
229
230 desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
231 GFP_KERNEL);
232 if (!desc)
233 goto err;
234
235 desc->tfm = shash;
236 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
237
238 crypto_shash_init(desc);
239 crypto_shash_update(desc, data, datalen);
240 crypto_shash_update(desc, sig, sizeof(*sh));
241 crypto_shash_final(desc, hash);
242
243 kfree(desc);
244
245 /* pass signature mpis address */
246 err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
247 hash, sizeof(hash));
248
249 err:
250 key_put(key);
251
252 return err ? -EINVAL : 0;
253 }
254 EXPORT_SYMBOL_GPL(digsig_verify);
255
digsig_init(void)256 static int __init digsig_init(void)
257 {
258 shash = crypto_alloc_shash("sha1", 0, 0);
259 if (IS_ERR(shash)) {
260 pr_err("shash allocation failed\n");
261 return PTR_ERR(shash);
262 }
263
264 return 0;
265
266 }
267
digsig_cleanup(void)268 static void __exit digsig_cleanup(void)
269 {
270 crypto_free_shash(shash);
271 }
272
273 module_init(digsig_init);
274 module_exit(digsig_cleanup);
275
276 MODULE_LICENSE("GPL");
277