lib/digsig.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2011 Nokia Corporation
   4  * Copyright (C) 2011 Intel Corporation
   5  *
   6  * Author:
   7  * Dmitry Kasatkin <dmitry.kasatkin@nokia.com>
   8  *                 <dmitry.kasatkin@intel.com>
   9  *
  10  * File: sign.c
  11  *      implements signature (RSA) verification
  12  *      pkcs decoding is based on LibTomCrypt code
  13  */
  14
  15 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  16
  17 #include <linux/err.h>
  18 #include <linux/module.h>
  19 #include <linux/slab.h>
  20 #include <linux/key.h>
  21 #include <linux/crypto.h>
  22 #include <crypto/hash.h>
  23 #include <crypto/sha.h>
  24 #include <keys/user-type.h>
  25 #include <linux/mpi.h>
  26 #include <linux/digsig.h>
  27
  28 static struct crypto_shash *shash;
  29
  30 static const char *pkcs_1_v1_5_decode_emsa(const unsigned char *msg,
  31                                                 unsigned long  msglen,
  32                                                 unsigned long  modulus_bitlen,
  33                                                 unsigned long *outlen)
  34 {
  35         unsigned long modulus_len, ps_len, i;
  36
  37         modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
  38
  39         /* test message size */
  40         if ((msglen > modulus_len) || (modulus_len < 11))
  41                 return NULL;
  42
  43         /* separate encoded message */
  44         if (msg[0] != 0x00 || msg[1] != 0x01)
  45                 return NULL;
  46
  47         for (i = 2; i < modulus_len - 1; i++)
  48                 if (msg[i] != 0xFF)
  49                         break;
  50
  51         /* separator check */
  52         if (msg[i] != 0)
  53                 /* There was no octet with hexadecimal value 0x00
  54                 to separate ps from m. */
  55                 return NULL;
  56
  57         ps_len = i - 2;
  58
  59         *outlen = (msglen - (2 + ps_len + 1));
  60
  61         return msg + 2 + ps_len + 1;
  62 }
  63
  64 /*
  65  * RSA Signature verification with public key
  66  */
  67 static int digsig_verify_rsa(struct key *key,
  68                     const char *sig, int siglen,
  69                        const char *h, int hlen)
  70 {
  71         int err = -EINVAL;
  72         unsigned long len;
  73         unsigned long mlen, mblen;
  74         unsigned nret, l;
  75         int head, i;
  76         unsigned char *out1 = NULL;
  77         const char *m;
  78         MPI in = NULL, res = NULL, pkey[2];
  79         uint8_t *p, *datap;
  80         const uint8_t *endp;
  81         const struct user_key_payload *ukp;
  82         struct pubkey_hdr *pkh;
  83
  84         down_read(&key->sem);
  85         ukp = user_key_payload_locked(key);
  86
  87         if (!ukp) {
  88                 /* key was revoked before we acquired its semaphore */
  89                 err = -EKEYREVOKED;
  90                 goto err1;
  91         }
  92
  93         if (ukp->datalen < sizeof(*pkh))
  94                 goto err1;
  95
  96         pkh = (struct pubkey_hdr *)ukp->data;
  97
  98         if (pkh->version != 1)
  99                 goto err1;
 100
 101         if (pkh->algo != PUBKEY_ALGO_RSA)
 102                 goto err1;
 103
 104         if (pkh->nmpi != 2)
 105                 goto err1;
 106
 107         datap = pkh->mpi;
 108         endp = ukp->data + ukp->datalen;
 109
 110         for (i = 0; i < pkh->nmpi; i++) {
 111                 unsigned int remaining = endp - datap;
 112                 pkey[i] = mpi_read_from_buffer(datap, &remaining);
 113                 if (IS_ERR(pkey[i])) {
 114                         err = PTR_ERR(pkey[i]);
 115                         goto err;
 116                 }
 117                 datap += remaining;
 118         }
 119
 120         mblen = mpi_get_nbits(pkey[0]);
 121         mlen = DIV_ROUND_UP(mblen, 8);
 122
 123         if (mlen == 0) {
 124                 err = -EINVAL;
 125                 goto err;
 126         }
 127
 128         err = -ENOMEM;
 129
 130         out1 = kzalloc(mlen, GFP_KERNEL);
 131         if (!out1)
 132                 goto err;
 133
 134         nret = siglen;
 135         in = mpi_read_from_buffer(sig, &nret);
 136         if (IS_ERR(in)) {
 137                 err = PTR_ERR(in);
 138                 goto err;
 139         }
 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         kfree(p);
 166
 167         m = pkcs_1_v1_5_decode_emsa(out1, len, mblen, &len);
 168
 169         if (!m || len != hlen || memcmp(m, h, hlen))
 170                 err = -EINVAL;
 171
 172 err:
 173         mpi_free(in);
 174         mpi_free(res);
 175         kfree(out1);
 176         while (--i >= 0)
 177                 mpi_free(pkey[i]);
 178 err1:
 179         up_read(&key->sem);
 180
 181         return err;
 182 }
 183
 184 /**
 185  * digsig_verify() - digital signature verification with public key
 186  * @keyring:    keyring to search key in
 187  * @sig:        digital signature
 188  * @siglen:     length of the signature
 189  * @data:       data
 190  * @datalen:    length of the data
 191  *
 192  * Returns 0 on success, -EINVAL otherwise
 193  *
 194  * Verifies data integrity against digital signature.
 195  * Currently only RSA is supported.
 196  * Normally hash of the content is used as a data for this function.
 197  *
 198  */
 199 int digsig_verify(struct key *keyring, const char *sig, int siglen,
 200                                                 const char *data, int datalen)
 201 {
 202         int err = -ENOMEM;
 203         struct signature_hdr *sh = (struct signature_hdr *)sig;
 204         struct shash_desc *desc = NULL;
 205         unsigned char hash[SHA1_DIGEST_SIZE];
 206         struct key *key;
 207         char name[20];
 208
 209         if (siglen < sizeof(*sh) + 2)
 210                 return -EINVAL;
 211
 212         if (sh->algo != PUBKEY_ALGO_RSA)
 213                 return -ENOTSUPP;
 214
 215         sprintf(name, "%llX", __be64_to_cpup((uint64_t *)sh->keyid));
 216
 217         if (keyring) {
 218                 /* search in specific keyring */
 219                 key_ref_t kref;
 220                 kref = keyring_search(make_key_ref(keyring, 1UL),
 221                                       &key_type_user, name, true);
 222                 if (IS_ERR(kref))
 223                         key = ERR_CAST(kref);
 224                 else
 225                         key = key_ref_to_ptr(kref);
 226         } else {
 227                 key = request_key(&key_type_user, name, NULL);
 228         }
 229         if (IS_ERR(key)) {
 230                 pr_err("key not found, id: %s\n", name);
 231                 return PTR_ERR(key);
 232         }
 233
 234         desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
 235                        GFP_KERNEL);
 236         if (!desc)
 237                 goto err;
 238
 239         desc->tfm = shash;
 240
 241         crypto_shash_init(desc);
 242         crypto_shash_update(desc, data, datalen);
 243         crypto_shash_update(desc, sig, sizeof(*sh));
 244         crypto_shash_final(desc, hash);
 245
 246         kfree(desc);
 247
 248         /* pass signature mpis address */
 249         err = digsig_verify_rsa(key, sig + sizeof(*sh), siglen - sizeof(*sh),
 250                              hash, sizeof(hash));
 251
 252 err:
 253         key_put(key);
 254
 255         return err ? -EINVAL : 0;
 256 }
 257 EXPORT_SYMBOL_GPL(digsig_verify);
 258
 259 static int __init digsig_init(void)
 260 {
 261         shash = crypto_alloc_shash("sha1", 0, 0);
 262         if (IS_ERR(shash)) {
 263                 pr_err("shash allocation failed\n");
 264                 return  PTR_ERR(shash);
 265         }
 266
 267         return 0;
 268
 269 }
 270
 271 static void __exit digsig_cleanup(void)
 272 {
 273         crypto_free_shash(shash);
 274 }
 275
 276 module_init(digsig_init);
 277 module_exit(digsig_cleanup);
 278
 279 MODULE_LICENSE("GPL");