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TOMOYO Linux Cross Reference
Linux/lib/digsig.c

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  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, *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) {
 90                 /* key was revoked before we acquired its semaphore */
 91                 err = -EKEYREVOKED;
 92                 goto err1;
 93         }
 94 
 95         if (ukp->datalen < sizeof(*pkh))
 96                 goto err1;
 97 
 98         pkh = (struct pubkey_hdr *)ukp->data;
 99 
100         if (pkh->version != 1)
101                 goto err1;
102 
103         if (pkh->algo != PUBKEY_ALGO_RSA)
104                 goto err1;
105 
106         if (pkh->nmpi != 2)
107                 goto err1;
108 
109         datap = pkh->mpi;
110         endp = ukp->data + ukp->datalen;
111 
112         err = -ENOMEM;
113 
114         for (i = 0; i < pkh->nmpi; i++) {
115                 unsigned int remaining = endp - datap;
116                 pkey[i] = mpi_read_from_buffer(datap, &remaining);
117                 if (!pkey[i])
118                         goto err;
119                 datap += remaining;
120         }
121 
122         mblen = mpi_get_nbits(pkey[0]);
123         mlen = DIV_ROUND_UP(mblen, 8);
124 
125         if (mlen == 0)
126                 goto err;
127 
128         out1 = kzalloc(mlen, GFP_KERNEL);
129         if (!out1)
130                 goto err;
131 
132         nret = siglen;
133         in = mpi_read_from_buffer(sig, &nret);
134         if (!in)
135                 goto err;
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         memset(out1, 0, head);
159         memcpy(out1 + head, p, l);
160 
161         kfree(p);
162 
163         m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
164 
165         if (!m || len != hlen || memcmp(m, h, hlen))
166                 err = -EINVAL;
167 
168 err:
169         mpi_free(in);
170         mpi_free(res);
171         kfree(out1);
172         while (--i >= 0)
173                 mpi_free(pkey[i]);
174 err1:
175         up_read(&key->sem);
176 
177         return err;
178 }
179 
180 /**
181  * digsig_verify() - digital signature verification with public key
182  * @keyring:    keyring to search key in
183  * @sig:        digital signature
184  * @sigen:      length of the signature
185  * @data:       data
186  * @datalen:    length of the data
187  * @return:     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  */
194 int digsig_verify(struct key *keyring, const char *sig, int siglen,
195                                                 const char *data, int datalen)
196 {
197         int err = -ENOMEM;
198         struct signature_hdr *sh = (struct signature_hdr *)sig;
199         struct shash_desc *desc = NULL;
200         unsigned char hash[SHA1_DIGEST_SIZE];
201         struct key *key;
202         char name[20];
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);
217                 if (IS_ERR(kref))
218                         key = ERR_PTR(PTR_ERR(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         desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
230                        GFP_KERNEL);
231         if (!desc)
232                 goto err;
233 
234         desc->tfm = shash;
235         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
236 
237         crypto_shash_init(desc);
238         crypto_shash_update(desc, data, datalen);
239         crypto_shash_update(desc, sig, sizeof(*sh));
240         crypto_shash_final(desc, hash);
241 
242         kfree(desc);
243 
244         /* pass signature mpis address */
245         err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
246                              hash, sizeof(hash));
247 
248 err:
249         key_put(key);
250 
251         return err ? -EINVAL : 0;
252 }
253 EXPORT_SYMBOL_GPL(digsig_verify);
254 
255 static int __init digsig_init(void)
256 {
257         shash = crypto_alloc_shash("sha1", 0, 0);
258         if (IS_ERR(shash)) {
259                 pr_err("shash allocation failed\n");
260                 return  PTR_ERR(shash);
261         }
262 
263         return 0;
264 
265 }
266 
267 static void __exit digsig_cleanup(void)
268 {
269         crypto_free_shash(shash);
270 }
271 
272 module_init(digsig_init);
273 module_exit(digsig_cleanup);
274 
275 MODULE_LICENSE("GPL");
276 

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