Root/lib/digsig.c

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
31static struct crypto_shash *shash;
32
33static 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 */
70static 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->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    err = -ENOMEM;
107
108    for (i = 0; i < pkh->nmpi; i++) {
109        unsigned int remaining = endp - datap;
110        pkey[i] = mpi_read_from_buffer(datap, &remaining);
111        if (!pkey[i])
112            goto err;
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        goto err;
121
122    out1 = kzalloc(mlen, GFP_KERNEL);
123    if (!out1)
124        goto err;
125
126    nret = siglen;
127    in = mpi_read_from_buffer(sig, &nret);
128    if (!in)
129        goto err;
130
131    res = mpi_alloc(mpi_get_nlimbs(in) * 2);
132    if (!res)
133        goto err;
134
135    err = mpi_powm(res, in, pkey[1], pkey[0]);
136    if (err)
137        goto err;
138
139    if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
140        err = -EINVAL;
141        goto err;
142    }
143
144    p = mpi_get_buffer(res, &l, NULL);
145    if (!p) {
146        err = -EINVAL;
147        goto err;
148    }
149
150    len = mlen;
151    head = len - l;
152    memset(out1, 0, head);
153    memcpy(out1 + head, p, l);
154
155    kfree(p);
156
157    m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
158
159    if (!m || len != hlen || memcmp(m, h, hlen))
160        err = -EINVAL;
161
162err:
163    mpi_free(in);
164    mpi_free(res);
165    kfree(out1);
166    while (--i >= 0)
167        mpi_free(pkey[i]);
168err1:
169    up_read(&key->sem);
170
171    return err;
172}
173
174/**
175 * digsig_verify() - digital signature verification with public key
176 * @keyring: keyring to search key in
177 * @sig: digital signature
178 * @sigen: length of the signature
179 * @data: data
180 * @datalen: length of the data
181 * @return: 0 on success, -EINVAL otherwise
182 *
183 * Verifies data integrity against digital signature.
184 * Currently only RSA is supported.
185 * Normally hash of the content is used as a data for this function.
186 *
187 */
188int digsig_verify(struct key *keyring, const char *sig, int siglen,
189                        const char *data, int datalen)
190{
191    int err = -ENOMEM;
192    struct signature_hdr *sh = (struct signature_hdr *)sig;
193    struct shash_desc *desc = NULL;
194    unsigned char hash[SHA1_DIGEST_SIZE];
195    struct key *key;
196    char name[20];
197
198    if (siglen < sizeof(*sh) + 2)
199        return -EINVAL;
200
201    if (sh->algo != PUBKEY_ALGO_RSA)
202        return -ENOTSUPP;
203
204    sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
205
206    if (keyring) {
207        /* search in specific keyring */
208        key_ref_t kref;
209        kref = keyring_search(make_key_ref(keyring, 1UL),
210                        &key_type_user, name);
211        if (IS_ERR(kref))
212            key = ERR_CAST(kref);
213        else
214            key = key_ref_to_ptr(kref);
215    } else {
216        key = request_key(&key_type_user, name, NULL);
217    }
218    if (IS_ERR(key)) {
219        pr_err("key not found, id: %s\n", name);
220        return PTR_ERR(key);
221    }
222
223    desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
224               GFP_KERNEL);
225    if (!desc)
226        goto err;
227
228    desc->tfm = shash;
229    desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
230
231    crypto_shash_init(desc);
232    crypto_shash_update(desc, data, datalen);
233    crypto_shash_update(desc, sig, sizeof(*sh));
234    crypto_shash_final(desc, hash);
235
236    kfree(desc);
237
238    /* pass signature mpis address */
239    err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
240                 hash, sizeof(hash));
241
242err:
243    key_put(key);
244
245    return err ? -EINVAL : 0;
246}
247EXPORT_SYMBOL_GPL(digsig_verify);
248
249static int __init digsig_init(void)
250{
251    shash = crypto_alloc_shash("sha1", 0, 0);
252    if (IS_ERR(shash)) {
253        pr_err("shash allocation failed\n");
254        return PTR_ERR(shash);
255    }
256
257    return 0;
258
259}
260
261static void __exit digsig_cleanup(void)
262{
263    crypto_free_shash(shash);
264}
265
266module_init(digsig_init);
267module_exit(digsig_cleanup);
268
269MODULE_LICENSE("GPL");
270

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