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 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;
  83         const uint8_t *endp;
  84         const struct user_key_payload *ukp;
  85         struct pubkey_hdr *pkh;
  86
  87         down_read(&key->sem);
  88         ukp = user_key_payload_locked(key);
  89
  90         if (!ukp) {
  91                 /* key was revoked before we acquired its semaphore */
  92                 err = -EKEYREVOKED;
  93                 goto err1;
  94         }
  95
  96         if (ukp->datalen < sizeof(*pkh))
  97                 goto err1;
  98
  99         pkh = (struct pubkey_hdr *)ukp->data;
 100
 101         if (pkh->version != 1)
 102                 goto err1;
 103
 104         if (pkh->algo != PUBKEY_ALGO_RSA)
 105                 goto err1;
 106
 107         if (pkh->nmpi != 2)
 108                 goto err1;
 109
 110         datap = pkh->mpi;
 111         endp = ukp->data + ukp->datalen;
 112
 113         for (i = 0; i < pkh->nmpi; i++) {
 114                 unsigned int remaining = endp - datap;
 115                 pkey[i] = mpi_read_from_buffer(datap, &remaining);
 116                 if (IS_ERR(pkey[i])) {
 117                         err = PTR_ERR(pkey[i]);
 118                         goto err;
 119                 }
 120                 datap += remaining;
 121         }
 122
 123         mblen = mpi_get_nbits(pkey[0]);
 124         mlen = DIV_ROUND_UP(mblen, 8);
 125
 126         if (mlen == 0) {
 127                 err = -EINVAL;
 128                 goto err;
 129         }
 130
 131         err = -ENOMEM;
 132
 133         out1 = kzalloc(mlen, GFP_KERNEL);
 134         if (!out1)
 135                 goto err;
 136
 137         nret = siglen;
 138         in = mpi_read_from_buffer(sig, &nret);
 139         if (IS_ERR(in)) {
 140                 err = PTR_ERR(in);
 141                 goto err;
 142         }
 143
 144         res = mpi_alloc(mpi_get_nlimbs(in) * 2);
 145         if (!res)
 146                 goto err;
 147
 148         err = mpi_powm(res, in, pkey[1], pkey[0]);
 149         if (err)
 150                 goto err;
 151
 152         if (mpi_get_nlimbs(res) * BYTES_PER_MPI_LIMB > mlen) {
 153                 err = -EINVAL;
 154                 goto err;
 155         }
 156
 157         p = mpi_get_buffer(res, &l, NULL);
 158         if (!p) {
 159                 err = -EINVAL;
 160                 goto err;
 161         }
 162
 163         len = mlen;
 164         head = len - l;
 165         memset(out1, 0, head);
 166         memcpy(out1 + head, p, l);
 167
 168         kfree(p);
 169
 170         m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
 171
 172         if (!m || len != hlen || memcmp(m, h, hlen))
 173                 err = -EINVAL;
 174
 175 err:
 176         mpi_free(in);
 177         mpi_free(res);
 178         kfree(out1);
 179         while (--i >= 0)
 180                 mpi_free(pkey[i]);
 181 err1:
 182         up_read(&key->sem);
 183
 184         return err;
 185 }
 186
 187 /**
 188  * digsig_verify() - digital signature verification with public key
 189  * @keyring:    keyring to search key in
 190  * @sig:        digital signature
 191  * @siglen:     length of the signature
 192  * @data:       data
 193  * @datalen:    length of the data
 194  *
 195  * Returns 0 on success, -EINVAL otherwise
 196  *
 197  * Verifies data integrity against digital signature.
 198  * Currently only RSA is supported.
 199  * Normally hash of the content is used as a data for this function.
 200  *
 201  */
 202 int digsig_verify(struct key *keyring, const char *sig, int siglen,
 203                                                 const char *data, int datalen)
 204 {
 205         int err = -ENOMEM;
 206         struct signature_hdr *sh = (struct signature_hdr *)sig;
 207         struct shash_desc *desc = NULL;
 208         unsigned char hash[SHA1_DIGEST_SIZE];
 209         struct key *key;
 210         char name[20];
 211
 212         if (siglen < sizeof(*sh) + 2)
 213                 return -EINVAL;
 214
 215         if (sh->algo != PUBKEY_ALGO_RSA)
 216                 return -ENOTSUPP;
 217
 218         sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
 219
 220         if (keyring) {
 221                 /* search in specific keyring */
 222                 key_ref_t kref;
 223                 kref = keyring_search(make_key_ref(keyring, 1UL),
 224                                                 &key_type_user, name);
 225                 if (IS_ERR(kref))
 226                         key = ERR_CAST(kref);
 227                 else
 228                         key = key_ref_to_ptr(kref);
 229         } else {
 230                 key = request_key(&key_type_user, name, NULL);
 231         }
 232         if (IS_ERR(key)) {
 233                 pr_err("key not found, id: %s\n", name);
 234                 return PTR_ERR(key);
 235         }
 236
 237         desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
 238                        GFP_KERNEL);
 239         if (!desc)
 240                 goto err;
 241
 242         desc->tfm = shash;
 243         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 244
 245         crypto_shash_init(desc);
 246         crypto_shash_update(desc, data, datalen);
 247         crypto_shash_update(desc, sig, sizeof(*sh));
 248         crypto_shash_final(desc, hash);
 249
 250         kfree(desc);
 251
 252         /* pass signature mpis address */
 253         err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
 254                              hash, sizeof(hash));
 255
 256 err:
 257         key_put(key);
 258
 259         return err ? -EINVAL : 0;
 260 }
 261 EXPORT_SYMBOL_GPL(digsig_verify);
 262
 263 static int __init digsig_init(void)
 264 {
 265         shash = crypto_alloc_shash("sha1", 0, 0);
 266         if (IS_ERR(shash)) {
 267                 pr_err("shash allocation failed\n");
 268                 return  PTR_ERR(shash);
 269         }
 270
 271         return 0;
 272
 273 }
 274
 275 static void __exit digsig_cleanup(void)
 276 {
 277         crypto_free_shash(shash);
 278 }
 279
 280 module_init(digsig_init);
 281 module_exit(digsig_cleanup);
 282
 283 MODULE_LICENSE("GPL");