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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->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 
162 err:
163         mpi_free(in);
164         mpi_free(res);
165         kfree(out1);
166         while (--i >= 0)
167                 mpi_free(pkey[i]);
168 err1:
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  */
188 int 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_PTR(PTR_ERR(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 
242 err:
243         key_put(key);
244 
245         return err ? -EINVAL : 0;
246 }
247 EXPORT_SYMBOL_GPL(digsig_verify);
248 
249 static 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 
261 static void __exit digsig_cleanup(void)
262 {
263         crypto_free_shash(shash);
264 }
265 
266 module_init(digsig_init);
267 module_exit(digsig_cleanup);
268 
269 MODULE_LICENSE("GPL");
270 

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