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Linux/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 
 31 static struct crypto_shash *shash;
 32 
 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  */
 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;
 83         const uint8_t *endp;
 84         const struct user_key_payload *ukp;
 85         struct pubkey_hdr *pkh;
 86 
 87         down_read(&key->sem);
 88         ukp = user_key_payload(key);
 89 
 90         if (ukp->datalen < sizeof(*pkh))
 91                 goto err1;
 92 
 93         pkh = (struct pubkey_hdr *)ukp->data;
 94 
 95         if (pkh->version != 1)
 96                 goto err1;
 97 
 98         if (pkh->algo != PUBKEY_ALGO_RSA)
 99                 goto err1;
100 
101         if (pkh->nmpi != 2)
102                 goto err1;
103 
104         datap = pkh->mpi;
105         endp = ukp->data + ukp->datalen;
106 
107         for (i = 0; i < pkh->nmpi; i++) {
108                 unsigned int remaining = endp - datap;
109                 pkey[i] = mpi_read_from_buffer(datap, &remaining);
110                 if (IS_ERR(pkey[i])) {
111                         err = PTR_ERR(pkey[i]);
112                         goto err;
113                 }
114                 datap += remaining;
115         }
116 
117         mblen = mpi_get_nbits(pkey[0]);
118         mlen = DIV_ROUND_UP(mblen, 8);
119 
120         if (mlen == 0) {
121                 err = -EINVAL;
122                 goto err;
123         }
124 
125         err = -ENOMEM;
126 
127         out1 = kzalloc(mlen, GFP_KERNEL);
128         if (!out1)
129                 goto err;
130 
131         nret = siglen;
132         in = mpi_read_from_buffer(sig, &nret);
133         if (IS_ERR(in)) {
134                 err = PTR_ERR(in);
135                 goto err;
136         }
137 
138         res = mpi_alloc(mpi_get_nlimbs(in) * 2);
139         if (!res)
140                 goto err;
141 
142         err = mpi_powm(res, in, pkey[1], pkey[0]);
143         if (err)
144                 goto err;
145 
146         if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
147                 err = -EINVAL;
148                 goto err;
149         }
150 
151         p = mpi_get_buffer(res, &l, NULL);
152         if (!p) {
153                 err = -EINVAL;
154                 goto err;
155         }
156 
157         len = mlen;
158         head = len - l;
159         memset(out1, 0, head);
160         memcpy(out1 + head, p, l);
161 
162         kfree(p);
163 
164         m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
165 
166         if (!m || len != hlen || memcmp(m, h, hlen))
167                 err = -EINVAL;
168 
169 err:
170         mpi_free(in);
171         mpi_free(res);
172         kfree(out1);
173         while (--i >= 0)
174                 mpi_free(pkey[i]);
175 err1:
176         up_read(&key->sem);
177 
178         return err;
179 }
180 
181 /**
182  * digsig_verify() - digital signature verification with public key
183  * @keyring:    keyring to search key in
184  * @sig:        digital signature
185  * @siglen:     length of the signature
186  * @data:       data
187  * @datalen:    length of the data
188  *
189  * Returns 0 on success, -EINVAL otherwise
190  *
191  * Verifies data integrity against digital signature.
192  * Currently only RSA is supported.
193  * Normally hash of the content is used as a data for this function.
194  *
195  */
196 int digsig_verify(struct key *keyring, const char *sig, int siglen,
197                                                 const char *data, int datalen)
198 {
199         int err = -ENOMEM;
200         struct signature_hdr *sh = (struct signature_hdr *)sig;
201         struct shash_desc *desc = NULL;
202         unsigned char hash[SHA1_DIGEST_SIZE];
203         struct key *key;
204         char name[20];
205 
206         if (siglen < sizeof(*sh) + 2)
207                 return -EINVAL;
208 
209         if (sh->algo != PUBKEY_ALGO_RSA)
210                 return -ENOTSUPP;
211 
212         sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
213 
214         if (keyring) {
215                 /* search in specific keyring */
216                 key_ref_t kref;
217                 kref = keyring_search(make_key_ref(keyring, 1UL),
218                                                 &key_type_user, name);
219                 if (IS_ERR(kref))
220                         key = ERR_CAST(kref);
221                 else
222                         key = key_ref_to_ptr(kref);
223         } else {
224                 key = request_key(&key_type_user, name, NULL);
225         }
226         if (IS_ERR(key)) {
227                 pr_err("key not found, id: %s\n", name);
228                 return PTR_ERR(key);
229         }
230 
231         desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
232                        GFP_KERNEL);
233         if (!desc)
234                 goto err;
235 
236         desc->tfm = shash;
237         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
238 
239         crypto_shash_init(desc);
240         crypto_shash_update(desc, data, datalen);
241         crypto_shash_update(desc, sig, sizeof(*sh));
242         crypto_shash_final(desc, hash);
243 
244         kfree(desc);
245 
246         /* pass signature mpis address */
247         err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
248                              hash, sizeof(hash));
249 
250 err:
251         key_put(key);
252 
253         return err ? -EINVAL : 0;
254 }
255 EXPORT_SYMBOL_GPL(digsig_verify);
256 
257 static int __init digsig_init(void)
258 {
259         shash = crypto_alloc_shash("sha1", 0, 0);
260         if (IS_ERR(shash)) {
261                 pr_err("shash allocation failed\n");
262                 return  PTR_ERR(shash);
263         }
264 
265         return 0;
266 
267 }
268 
269 static void __exit digsig_cleanup(void)
270 {
271         crypto_free_shash(shash);
272 }
273 
274 module_init(digsig_init);
275 module_exit(digsig_cleanup);
276 
277 MODULE_LICENSE("GPL");
278 

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