digsig.c

  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 <crypto/sha1.h>
 22#include <keys/user-type.h>
 23#include <linux/mpi.h>
 24#include <linux/digsig.h>
 25
 26static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
 27						unsigned long  msglen,
 28						unsigned long  modulus_bitlen,
 29						unsigned long *outlen)
 30{
 31	unsigned long modulus_len, ps_len, i;
 32
 33	modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
 34
 35	/* test message size */
 36	if ((msglen > modulus_len) || (modulus_len < 11))
 37		return NULL;
 38
 39	/* separate encoded message */
 40	if (msg[0] != 0x00 || msg[1] != 0x01)
 41		return NULL;
 42
 43	for (i = 2; i < modulus_len - 1; i++)
 44		if (msg[i] != 0xFF)
 45			break;
 46
 47	/* separator check */
 48	if (msg[i] != 0)
 49		/* There was no octet with hexadecimal value 0x00
 50		to separate ps from m. */
 51		return NULL;
 52
 53	ps_len = i - 2;
 54
 55	*outlen = (msglen - (2 + ps_len + 1));
 56
 57	return msg + 2 + ps_len + 1;
 58}
 59
 60/*
 61 * RSA Signature verification with public key
 62 */
 63static int digsig_verify_rsa(struct key *key,
 64		    const char *sig, int siglen,
 65		       const char *h, int hlen)
 66{
 67	int err = -EINVAL;
 68	unsigned long len;
 69	unsigned long mlen, mblen;
 70	unsigned nret, l;
 71	int head, i;
 72	unsigned char *out1 = NULL;
 73	const char *m;
 74	MPI in = NULL, res = NULL, pkey[2];
 75	uint8_t *p, *datap;
 76	const uint8_t *endp;
 77	const struct user_key_payload *ukp;
 78	struct pubkey_hdr *pkh;
 79
 80	down_read(&key->sem);
 81	ukp = user_key_payload_locked(key);
 82
 83	if (!ukp) {
 84		/* key was revoked before we acquired its semaphore */
 85		err = -EKEYREVOKED;
 86		goto err1;
 87	}
 88
 89	if (ukp->datalen < sizeof(*pkh))
 90		goto err1;
 91
 92	pkh = (struct pubkey_hdr *)ukp->data;
 93
 94	if (pkh->version != 1)
 95		goto err1;
 96
 97	if (pkh->algo != PUBKEY_ALGO_RSA)
 98		goto err1;
 99
100	if (pkh->nmpi != 2)
101		goto err1;
102
103	datap = pkh->mpi;
104	endp = ukp->data + ukp->datalen;
105
106	for (i = 0; i < pkh->nmpi; i++) {
107		unsigned int remaining = endp - datap;
108		pkey[i] = mpi_read_from_buffer(datap, &remaining);
109		if (IS_ERR(pkey[i])) {
110			err = PTR_ERR(pkey[i]);
111			goto err;
112		}
113		datap += remaining;
114	}
115
116	mblen = mpi_get_nbits(pkey[0]);
117	mlen = DIV_ROUND_UP(mblen, 8);
118
119	if (mlen == 0) {
120		err = -EINVAL;
121		goto err;
122	}
123
124	err = -ENOMEM;
125
126	out1 = kzalloc(mlen, GFP_KERNEL);
127	if (!out1)
128		goto err;
129
130	nret = siglen;
131	in = mpi_read_from_buffer(sig, &nret);
132	if (IS_ERR(in)) {
133		err = PTR_ERR(in);
134		goto err;
135	}
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	memcpy(out1 + head, p, l);
159
160	kfree(p);
161
162	m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
163
164	if (!m || len != hlen || memcmp(m, h, hlen))
165		err = -EINVAL;
166
167err:
168	mpi_free(in);
169	mpi_free(res);
170	kfree(out1);
171	while (--i >= 0)
172		mpi_free(pkey[i]);
173err1:
174	up_read(&key->sem);
175
176	return err;
177}
178
179/**
180 * digsig_verify() - digital signature verification with public key
181 * @keyring:	keyring to search key in
182 * @sig:	digital signature
183 * @siglen:	length of the signature
184 * @data:	data
185 * @datalen:	length of the data
186 *
187 * Returns 0 on success, -EINVAL otherwise
188 *
189 * Verifies data integrity against digital signature.
190 * Currently only RSA is supported.
191 * Normally hash of the content is used as a data for this function.
192 *
193 */
194int digsig_verify(struct key *keyring, const char *sig, int siglen,
195						const char *data, int datalen)
196{
197	struct signature_hdr *sh = (struct signature_hdr *)sig;
198	struct sha1_ctx ctx;
199	unsigned char hash[SHA1_DIGEST_SIZE];
200	struct key *key;
201	char name[20];
202	int err;
203
204	if (siglen < sizeof(*sh) + 2)
205		return -EINVAL;
206
207	if (sh->algo != PUBKEY_ALGO_RSA)
208		return -ENOTSUPP;
209
210	sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
211
212	if (keyring) {
213		/* search in specific keyring */
214		key_ref_t kref;
215		kref = keyring_search(make_key_ref(keyring, 1UL),
216				      &key_type_user, name, true);
217		if (IS_ERR(kref))
218			key = ERR_CAST(kref);
219		else
220			key = key_ref_to_ptr(kref);
221	} else {
222		key = request_key(&key_type_user, name, NULL);
223	}
224	if (IS_ERR(key)) {
225		pr_err("key not found, id: %s\n", name);
226		return PTR_ERR(key);
227	}
228
229	sha1_init(&ctx);
230	sha1_update(&ctx, data, datalen);
231	sha1_update(&ctx, sig, sizeof(*sh));
232	sha1_final(&ctx, hash);
233
234	/* pass signature mpis address */
235	err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
236			     hash, sizeof(hash));
237
238	key_put(key);
239
240	return err ? -EINVAL : 0;
241}
242EXPORT_SYMBOL_GPL(digsig_verify);
243
244MODULE_LICENSE("GPL");