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
28static struct crypto_shash *shash;
29
30static 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 */
67static 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88		/* key was revoked before we acquired its semaphore */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
172err:
173	mpi_free(in);
174	mpi_free(res);
175	kfree(out1);
176	while (--i >= 0)
177		mpi_free(pkey[i]);
178err1:
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 */
199int 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
252err:
253	key_put(key);
254
255	return err ? -EINVAL : 0;
256}
257EXPORT_SYMBOL_GPL(digsig_verify);
258
259static 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
271static void __exit digsig_cleanup(void)
272{
273	crypto_free_shash(shash);
274}
275
276module_init(digsig_init);
277module_exit(digsig_cleanup);
278
279MODULE_LICENSE("GPL");
280