summaryrefslogtreecommitdiff
path: root/lib/digsig.c
blob: 3782af401c685c92f5f224beb61cf24fcf957ee7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
/*
 * Copyright (C) 2011 Nokia Corporation
 * Copyright (C) 2011 Intel Corporation
 *
 * Author:
 * Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
 *                 <dmitry.kasatkin@intel.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 2 of the License.
 *
 * File: sign.c
 *	implements signature (RSA) verification
 *	pkcs decoding is based on LibTomCrypt code
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/err.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/key.h>
#include <linux/crypto.h>
#include <crypto/hash.h>
#include <crypto/sha.h>
#include <keys/user-type.h>
#include <linux/mpi.h>
#include <linux/digsig.h>

static struct crypto_shash *shash;

static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
						unsigned long  msglen,
						unsigned long  modulus_bitlen,
						unsigned long *outlen)
{
	unsigned long modulus_len, ps_len, i;

	modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);

	/* test message size */
	if ((msglen > modulus_len) || (modulus_len < 11))
		return NULL;

	/* separate encoded message */
	if (msg[0] != 0x00 || msg[1] != 0x01)
		return NULL;

	for (i = 2; i < modulus_len - 1; i++)
		if (msg[i] != 0xFF)
			break;

	/* separator check */
	if (msg[i] != 0)
		/* There was no octet with hexadecimal value 0x00
		to separate ps from m. */
		return NULL;

	ps_len = i - 2;

	*outlen = (msglen - (2 + ps_len + 1));

	return msg + 2 + ps_len + 1;
}

/*
 * RSA Signature verification with public key
 */
static int digsig_verify_rsa(struct key *key,
		    const char *sig, int siglen,
		       const char *h, int hlen)
{
	int err = -EINVAL;
	unsigned long len;
	unsigned long mlen, mblen;
	unsigned nret, l;
	int head, i;
	unsigned char *out1 = NULL;
	const char *m;
	MPI in = NULL, res = NULL, pkey[2];
	uint8_t *p, *datap;
	const uint8_t *endp;
	const struct user_key_payload *ukp;
	struct pubkey_hdr *pkh;

	down_read(&key->sem);
	ukp = user_key_payload_locked(key);

	if (!ukp) {
		/* key was revoked before we acquired its semaphore */
		err = -EKEYREVOKED;
		goto err1;
	}

	if (ukp->datalen < sizeof(*pkh))
		goto err1;

	pkh = (struct pubkey_hdr *)ukp->data;

	if (pkh->version != 1)
		goto err1;

	if (pkh->algo != PUBKEY_ALGO_RSA)
		goto err1;

	if (pkh->nmpi != 2)
		goto err1;

	datap = pkh->mpi;
	endp = ukp->data + ukp->datalen;

	for (i = 0; i < pkh->nmpi; i++) {
		unsigned int remaining = endp - datap;
		pkey[i] = mpi_read_from_buffer(datap, &remaining);
		if (IS_ERR(pkey[i])) {
			err = PTR_ERR(pkey[i]);
			goto err;
		}
		datap += remaining;
	}

	mblen = mpi_get_nbits(pkey[0]);
	mlen = DIV_ROUND_UP(mblen, 8);

	if (mlen == 0) {
		err = -EINVAL;
		goto err;
	}

	err = -ENOMEM;

	out1 = kzalloc(mlen, GFP_KERNEL);
	if (!out1)
		goto err;

	nret = siglen;
	in = mpi_read_from_buffer(sig, &nret);
	if (IS_ERR(in)) {
		err = PTR_ERR(in);
		goto err;
	}

	res = mpi_alloc(mpi_get_nlimbs(in) * 2);
	if (!res)
		goto err;

	err = mpi_powm(res, in, pkey[1], pkey[0]);
	if (err)
		goto err;

	if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
		err = -EINVAL;
		goto err;
	}

	p = mpi_get_buffer(res, &l, NULL);
	if (!p) {
		err = -EINVAL;
		goto err;
	}

	len = mlen;
	head = len - l;
	memset(out1, 0, head);
	memcpy(out1 + head, p, l);

	kfree(p);

	m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);

	if (!m || len != hlen || memcmp(m, h, hlen))
		err = -EINVAL;

err:
	mpi_free(in);
	mpi_free(res);
	kfree(out1);
	while (--i >= 0)
		mpi_free(pkey[i]);
err1:
	up_read(&key->sem);

	return err;
}

/**
 * digsig_verify() - digital signature verification with public key
 * @keyring:	keyring to search key in
 * @sig:	digital signature
 * @siglen:	length of the signature
 * @data:	data
 * @datalen:	length of the data
 *
 * Returns 0 on success, -EINVAL otherwise
 *
 * Verifies data integrity against digital signature.
 * Currently only RSA is supported.
 * Normally hash of the content is used as a data for this function.
 *
 */
int digsig_verify(struct key *keyring, const char *sig, int siglen,
						const char *data, int datalen)
{
	int err = -ENOMEM;
	struct signature_hdr *sh = (struct signature_hdr *)sig;
	struct shash_desc *desc = NULL;
	unsigned char hash[SHA1_DIGEST_SIZE];
	struct key *key;
	char name[20];

	if (siglen < sizeof(*sh) + 2)
		return -EINVAL;

	if (sh->algo != PUBKEY_ALGO_RSA)
		return -ENOTSUPP;

	sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));

	if (keyring) {
		/* search in specific keyring */
		key_ref_t kref;
		kref = keyring_search(make_key_ref(keyring, 1UL),
				      &key_type_user, name, true);
		if (IS_ERR(kref))
			key = ERR_CAST(kref);
		else
			key = key_ref_to_ptr(kref);
	} else {
		key = request_key(&key_type_user, name, NULL);
	}
	if (IS_ERR(key)) {
		pr_err("key not found, id: %s\n", name);
		return PTR_ERR(key);
	}

	desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
		       GFP_KERNEL);
	if (!desc)
		goto err;

	desc->tfm = shash;

	crypto_shash_init(desc);
	crypto_shash_update(desc, data, datalen);
	crypto_shash_update(desc, sig, sizeof(*sh));
	crypto_shash_final(desc, hash);

	kfree(desc);

	/* pass signature mpis address */
	err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
			     hash, sizeof(hash));

err:
	key_put(key);

	return err ? -EINVAL : 0;
}
EXPORT_SYMBOL_GPL(digsig_verify);

static int __init digsig_init(void)
{
	shash = crypto_alloc_shash("sha1", 0, 0);
	if (IS_ERR(shash)) {
		pr_err("shash allocation failed\n");
		return  PTR_ERR(shash);
	}

	return 0;

}

static void __exit digsig_cleanup(void)
{
	crypto_free_shash(shash);
}

module_init(digsig_init);
module_exit(digsig_cleanup);

MODULE_LICENSE("GPL");