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, *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  * @siglen:     length of the signature
 179  * @data:       data
 180  * @datalen:    length of the data
 181  *
 182  * Returns 0 on success, -EINVAL otherwise
 183  *
 184  * Verifies data integrity against digital signature.
 185  * Currently only RSA is supported.
 186  * Normally hash of the content is used as a data for this function.
 187  *
 188  */
 189 int digsig_verify(struct key *keyring, const char *sig, int siglen,
 190                                                 const char *data, int datalen)
 191 {
 192         int err = -ENOMEM;
 193         struct signature_hdr *sh = (struct signature_hdr *)sig;
 194         struct shash_desc *desc = NULL;
 195         unsigned char hash[SHA1_DIGEST_SIZE];
 196         struct key *key;
 197         char name[20];
 198
 199         if (siglen < sizeof(*sh) + 2)
 200                 return -EINVAL;
 201
 202         if (sh->algo != PUBKEY_ALGO_RSA)
 203                 return -ENOTSUPP;
 204
 205         sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
 206
 207         if (keyring) {
 208                 /* search in specific keyring */
 209                 key_ref_t kref;
 210                 kref = keyring_search(make_key_ref(keyring, 1UL),
 211                                                 &key_type_user, name);
 212                 if (IS_ERR(kref))
 213                         key = ERR_CAST(kref);
 214                 else
 215                         key = key_ref_to_ptr(kref);
 216         } else {
 217                 key = request_key(&key_type_user, name, NULL);
 218         }
 219         if (IS_ERR(key)) {
 220                 pr_err("key not found, id: %s\n", name);
 221                 return PTR_ERR(key);
 222         }
 223
 224         desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
 225                        GFP_KERNEL);
 226         if (!desc)
 227                 goto err;
 228
 229         desc->tfm = shash;
 230         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
 231
 232         crypto_shash_init(desc);
 233         crypto_shash_update(desc, data, datalen);
 234         crypto_shash_update(desc, sig, sizeof(*sh));
 235         crypto_shash_final(desc, hash);
 236
 237         kfree(desc);
 238
 239         /* pass signature mpis address */
 240         err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
 241                              hash, sizeof(hash));
 242
 243 err:
 244         key_put(key);
 245
 246         return err ? -EINVAL : 0;
 247 }
 248 EXPORT_SYMBOL_GPL(digsig_verify);
 249
 250 static int __init digsig_init(void)
 251 {
 252         shash = crypto_alloc_shash("sha1", 0, 0);
 253         if (IS_ERR(shash)) {
 254                 pr_err("shash allocation failed\n");
 255                 return  PTR_ERR(shash);
 256         }
 257
 258         return 0;
 259
 260 }
 261
 262 static void __exit digsig_cleanup(void)
 263 {
 264         crypto_free_shash(shash);
 265 }
 266
 267 module_init(digsig_init);
 268 module_exit(digsig_cleanup);
 269
 270 MODULE_LICENSE("GPL");