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