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 int pkcs_1_v1_5_decode_emsa(const unsigned char *msg, 34 unsigned long msglen, 35 unsigned long modulus_bitlen, 36 unsigned char *out, 37 unsigned long *outlen) 38 { 39 unsigned long modulus_len, ps_len, i; 40 41 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0); 42 43 /* test message size */ 44 if ((msglen > modulus_len) || (modulus_len < 11)) 45 return -EINVAL; 46 47 /* separate encoded message */ 48 if ((msg[0] != 0x00) || (msg[1] != (unsigned char)1)) 49 return -EINVAL; 50 51 for (i = 2; i < modulus_len - 1; i++) 52 if (msg[i] != 0xFF) 53 break; 54 55 /* separator check */ 56 if (msg[i] != 0) 57 /* There was no octet with hexadecimal value 0x00 58 to separate ps from m. */ 59 return -EINVAL; 60 61 ps_len = i - 2; 62 63 if (*outlen < (msglen - (2 + ps_len + 1))) { 64 *outlen = msglen - (2 + ps_len + 1); 65 return -EOVERFLOW; 66 } 67 68 *outlen = (msglen - (2 + ps_len + 1)); 69 memcpy(out, &msg[2 + ps_len + 1], *outlen); 70 71 return 0; 72 } 73 74 /* 75 * RSA Signature verification with public key 76 */ 77 static int digsig_verify_rsa(struct key *key, 78 const char *sig, int siglen, 79 const char *h, int hlen) 80 { 81 int err = -EINVAL; 82 unsigned long len; 83 unsigned long mlen, mblen; 84 unsigned nret, l; 85 int head, i; 86 unsigned char *out1 = NULL, *out2 = NULL; 87 MPI in = NULL, res = NULL, pkey[2]; 88 uint8_t *p, *datap, *endp; 89 struct user_key_payload *ukp; 90 struct pubkey_hdr *pkh; 91 92 down_read(&key->sem); 93 ukp = key->payload.data; 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 = (mblen + 7)/8; 124 125 if (mlen == 0) 126 goto err; 127 128 out1 = kzalloc(mlen, GFP_KERNEL); 129 if (!out1) 130 goto err; 131 132 out2 = kzalloc(mlen, GFP_KERNEL); 133 if (!out2) 134 goto err; 135 136 nret = siglen; 137 in = mpi_read_from_buffer(sig, &nret); 138 if (!in) 139 goto err; 140 141 res = mpi_alloc(mpi_get_nlimbs(in) * 2); 142 if (!res) 143 goto err; 144 145 err = mpi_powm(res, in, pkey[1], pkey[0]); 146 if (err) 147 goto err; 148 149 if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) { 150 err = -EINVAL; 151 goto err; 152 } 153 154 p = mpi_get_buffer(res, &l, NULL); 155 if (!p) { 156 err = -EINVAL; 157 goto err; 158 } 159 160 len = mlen; 161 head = len - l; 162 memset(out1, 0, head); 163 memcpy(out1 + head, p, l); 164 165 err = pkcs_1_v1_5_decode_emsa(out1, len, mblen, out2, &len); 166 167 if (!err && len == hlen) 168 err = memcmp(out2, h, hlen); 169 170 err: 171 mpi_free(in); 172 mpi_free(res); 173 kfree(out1); 174 kfree(out2); 175 while (--i >= 0) 176 mpi_free(pkey[i]); 177 err1: 178 up_read(&key->sem); 179 180 return err; 181 } 182 183 /** 184 * digsig_verify() - digital signature verification with public key 185 * @keyring: keyring to search key in 186 * @sig: digital signature 187 * @sigen: length of the signature 188 * @data: data 189 * @datalen: length of the data 190 * @return: 0 on success, -EINVAL otherwise 191 * 192 * Verifies data integrity against digital signature. 193 * Currently only RSA is supported. 194 * Normally hash of the content is used as a data for this function. 195 * 196 */ 197 int digsig_verify(struct key *keyring, const char *sig, int siglen, 198 const char *data, int datalen) 199 { 200 int err = -ENOMEM; 201 struct signature_hdr *sh = (struct signature_hdr *)sig; 202 struct shash_desc *desc = NULL; 203 unsigned char hash[SHA1_DIGEST_SIZE]; 204 struct key *key; 205 char name[20]; 206 207 if (siglen < sizeof(*sh) + 2) 208 return -EINVAL; 209 210 if (sh->algo != PUBKEY_ALGO_RSA) 211 return -ENOTSUPP; 212 213 sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid)); 214 215 if (keyring) { 216 /* search in specific keyring */ 217 key_ref_t kref; 218 kref = keyring_search(make_key_ref(keyring, 1UL), 219 &key_type_user, name); 220 if (IS_ERR(kref)) 221 key = ERR_PTR(PTR_ERR(kref)); 222 else 223 key = key_ref_to_ptr(kref); 224 } else { 225 key = request_key(&key_type_user, name, NULL); 226 } 227 if (IS_ERR(key)) { 228 pr_err("key not found, id: %s\n", name); 229 return PTR_ERR(key); 230 } 231 232 desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash), 233 GFP_KERNEL); 234 if (!desc) 235 goto err; 236 237 desc->tfm = shash; 238 desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP; 239 240 crypto_shash_init(desc); 241 crypto_shash_update(desc, data, datalen); 242 crypto_shash_update(desc, sig, sizeof(*sh)); 243 crypto_shash_final(desc, hash); 244 245 kfree(desc); 246 247 /* pass signature mpis address */ 248 err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh), 249 hash, sizeof(hash)); 250 251 err: 252 key_put(key); 253 254 return err ? -EINVAL : 0; 255 } 256 EXPORT_SYMBOL_GPL(digsig_verify); 257 258 static int __init digsig_init(void) 259 { 260 shash = crypto_alloc_shash("sha1", 0, 0); 261 if (IS_ERR(shash)) { 262 pr_err("shash allocation failed\n"); 263 return PTR_ERR(shash); 264 } 265 266 return 0; 267 268 } 269 270 static void __exit digsig_cleanup(void) 271 { 272 crypto_free_shash(shash); 273 } 274 275 module_init(digsig_init); 276 module_exit(digsig_cleanup); 277 278 MODULE_LICENSE("GPL"); 279