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