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 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                         int *is_valid)
  39 {
  40         unsigned long modulus_len, ps_len, i;
  41         int result;
  42
  43         /* default to invalid packet */
  44         *is_valid = 0;
  45
  46         modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
  47
  48         /* test message size */
  49         if ((msglen > modulus_len) || (modulus_len < 11))
  50                 return -EINVAL;
  51
  52         /* separate encoded message */
  53         if ((msg[0] != 0x00) || (msg[1] != (unsigned char)1)) {
  54                 result = -EINVAL;
  55                 goto bail;
  56         }
  57
  58         for (i = 2; i < modulus_len - 1; i++)
  59                 if (msg[i] != 0xFF)
  60                         break;
  61
  62         /* separator check */
  63         if (msg[i] != 0) {
  64                 /* There was no octet with hexadecimal value 0x00
  65                 to separate ps from m. */
  66                 result = -EINVAL;
  67                 goto bail;
  68         }
  69
  70         ps_len = i - 2;
  71
  72         if (*outlen < (msglen - (2 + ps_len + 1))) {
  73                 *outlen = msglen - (2 + ps_len + 1);
  74                 result = -EOVERFLOW;
  75                 goto bail;
  76         }
  77
  78         *outlen = (msglen - (2 + ps_len + 1));
  79         memcpy(out, &msg[2 + ps_len + 1], *outlen);
  80
  81         /* valid packet */
  82         *is_valid = 1;
  83         result    = 0;
  84 bail:
  85         return result;
  86 }
  87
  88 /*
  89  * RSA Signature verification with public key
  90  */
  91 static int digsig_verify_rsa(struct key *key,
  92                     const char *sig, int siglen,
  93                        const char *h, int hlen)
  94 {
  95         int err = -EINVAL;
  96         unsigned long len;
  97         unsigned long mlen, mblen;
  98         unsigned nret, l;
  99         int valid, head, i;
 100         unsigned char *out1 = NULL, *out2 = NULL;
 101         MPI in = NULL, res = NULL, pkey[2];
 102         uint8_t *p, *datap, *endp;
 103         struct user_key_payload *ukp;
 104         struct pubkey_hdr *pkh;
 105
 106         down_read(&key->sem);
 107         ukp = key->payload.data;
 108         pkh = (struct pubkey_hdr *)ukp->data;
 109
 110         if (pkh->version != 1)
 111                 goto err1;
 112
 113         if (pkh->algo != PUBKEY_ALGO_RSA)
 114                 goto err1;
 115
 116         if (pkh->nmpi != 2)
 117                 goto err1;
 118
 119         datap = pkh->mpi;
 120         endp = datap + ukp->datalen;
 121
 122         for (i = 0; i < pkh->nmpi; i++) {
 123                 unsigned int remaining = endp - datap;
 124                 pkey[i] = mpi_read_from_buffer(datap, &remaining);
 125                 datap += remaining;
 126         }
 127
 128         mblen = mpi_get_nbits(pkey[0]);
 129         mlen = (mblen + 7)/8;
 130
 131         err = -ENOMEM;
 132
 133         out1 = kzalloc(mlen, GFP_KERNEL);
 134         if (!out1)
 135                 goto err;
 136
 137         out2 = kzalloc(mlen, GFP_KERNEL);
 138         if (!out2)
 139                 goto err;
 140
 141         nret = siglen;
 142         in = mpi_read_from_buffer(sig, &nret);
 143         if (!in)
 144                 goto err;
 145
 146         res = mpi_alloc(mpi_get_nlimbs(in) * 2);
 147         if (!res)
 148                 goto err;
 149
 150         err = mpi_powm(res, in, pkey[1], pkey[0]);
 151         if (err)
 152                 goto err;
 153
 154         if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
 155                 err = -EINVAL;
 156                 goto err;
 157         }
 158
 159         p = mpi_get_buffer(res, &l, NULL);
 160         if (!p) {
 161                 err = -EINVAL;
 162                 goto err;
 163         }
 164
 165         len = mlen;
 166         head = len - l;
 167         memset(out1, 0, head);
 168         memcpy(out1 + head, p, l);
 169
 170         err = -EINVAL;
 171         pkcs_1_v1_5_decode_emsa(out1, len, mblen, out2, &len, &valid);
 172
 173         if (valid && len == hlen)
 174                 err = memcmp(out2, h, hlen);
 175
 176 err:
 177         mpi_free(in);
 178         mpi_free(res);
 179         kfree(out1);
 180         kfree(out2);
 181         mpi_free(pkey[0]);
 182         mpi_free(pkey[1]);
 183 err1:
 184         up_read(&key->sem);
 185
 186         return err;
 187 }
 188
 189 /**
 190  * digsig_verify() - digital signature verification with public key
 191  * @keyring:    keyring to search key in
 192  * @sig:        digital signature
 193  * @sigen:      length of the signature
 194  * @data:       data
 195  * @datalen:    length of the data
 196  * @return:     0 on success, -EINVAL otherwise
 197  *
 198  * Verifies data integrity against digital signature.
 199  * Currently only RSA is supported.
 200  * Normally hash of the content is used as a data for this function.
 201  *
 202  */
 203 int digsig_verify(struct key *keyring, const char *sig, int siglen,
 204                                                 const char *data, int datalen)
 205 {
 206         int err = -ENOMEM;
 207         struct signature_hdr *sh = (struct signature_hdr *)sig;
 208         struct shash_desc *desc = NULL;
 209         unsigned char hash[SHA1_DIGEST_SIZE];
 210         struct key *key;
 211         char name[20];
 212
 213         if (siglen < sizeof(*sh) + 2)
 214                 return -EINVAL;
 215
 216         if (sh->algo != PUBKEY_ALGO_RSA)
 217                 return -ENOTSUPP;
 218
 219         sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
 220
 221         if (keyring) {
 222                 /* search in specific keyring */
 223                 key_ref_t kref;
 224                 kref = keyring_search(make_key_ref(keyring, 1UL),
 225                                                 &key_type_user, name);
 226                 if (IS_ERR(kref))
 227                         key = ERR_PTR(PTR_ERR(kref));
 228                 else
 229                         key = key_ref_to_ptr(kref);
 230         } else {
 231                 key = request_key(&key_type_user, name, NULL);
 232         }
 233         if (IS_ERR(key)) {
 234                 pr_err("key not found, id: %s\n", name);
 235                 return PTR_ERR(key);
 236         }
 237
 238         desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
 239                        GFP_KERNEL);
 240         if (!desc)
 241                 goto err;
 242
 243         desc->tfm = shash;
 244         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 245
 246         crypto_shash_init(desc);
 247         crypto_shash_update(desc, data, datalen);
 248         crypto_shash_update(desc, sig, sizeof(*sh));
 249         crypto_shash_final(desc, hash);
 250
 251         kfree(desc);
 252
 253         /* pass signature mpis address */
 254         err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
 255                              hash, sizeof(hash));
 256
 257 err:
 258         key_put(key);
 259
 260         return err ? -EINVAL : 0;
 261 }
 262 EXPORT_SYMBOL_GPL(digsig_verify);
 263
 264 static int __init digsig_init(void)
 265 {
 266         shash = crypto_alloc_shash("sha1", 0, 0);
 267         if (IS_ERR(shash)) {
 268                 pr_err("shash allocation failed\n");
 269                 return  PTR_ERR(shash);
 270         }
 271
 272         return 0;
 273
 274 }
 275
 276 static void __exit digsig_cleanup(void)
 277 {
 278         crypto_free_shash(shash);
 279 }
 280
 281 module_init(digsig_init);
 282 module_exit(digsig_cleanup);
 283
 284 MODULE_LICENSE("GPL");