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 {
  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");