kernel/module_signing.c

   1 /* Module signature checker
   2  *
   3  * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #include <linux/kernel.h>
  13 #include <linux/err.h>
  14 #include <crypto/public_key.h>
  15 #include <crypto/hash.h>
  16 #include <keys/asymmetric-type.h>
  17 #include "module-internal.h"
  18
  19 /*
  20  * Module signature information block.
  21  *
  22  * The constituents of the signature section are, in order:
  23  *
  24  *      - Signer's name
  25  *      - Key identifier
  26  *      - Signature data
  27  *      - Information block
  28  */
  29 struct module_signature {
  30         enum pkey_algo          algo : 8;       /* Public-key crypto algorithm */
  31         enum pkey_hash_algo     hash : 8;       /* Digest algorithm */
  32         enum pkey_id_type       id_type : 8;    /* Key identifier type */
  33         u8                      signer_len;     /* Length of signer's name */
  34         u8                      key_id_len;     /* Length of key identifier */
  35         u8                      __pad[3];
  36         __be32                  sig_len;        /* Length of signature data */
  37 };
  38
  39 /*
  40  * Digest the module contents.
  41  */
  42 static struct public_key_signature *mod_make_digest(enum pkey_hash_algo hash,
  43                                                     const void *mod,
  44                                                     unsigned long modlen)
  45 {
  46         struct public_key_signature *pks;
  47         struct crypto_shash *tfm;
  48         struct shash_desc *desc;
  49         size_t digest_size, desc_size;
  50         int ret;
  51
  52         pr_devel("==>%s()\n", __func__);
  53
  54         /* Allocate the hashing algorithm we're going to need and find out how
  55          * big the hash operational data will be.
  56          */
  57         tfm = crypto_alloc_shash(pkey_hash_algo[hash], 0, 0);
  58         if (IS_ERR(tfm))
  59                 return (PTR_ERR(tfm) == -ENOENT) ? ERR_PTR(-ENOPKG) : ERR_CAST(tfm);
  60
  61         desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
  62         digest_size = crypto_shash_digestsize(tfm);
  63
  64         /* We allocate the hash operational data storage on the end of our
  65          * context data and the digest output buffer on the end of that.
  66          */
  67         ret = -ENOMEM;
  68         pks = kzalloc(digest_size + sizeof(*pks) + desc_size, GFP_KERNEL);
  69         if (!pks)
  70                 goto error_no_pks;
  71
  72         pks->pkey_hash_algo     = hash;
  73         pks->digest             = (u8 *)pks + sizeof(*pks) + desc_size;
  74         pks->digest_size        = digest_size;
  75
  76         desc = (void *)pks + sizeof(*pks);
  77         desc->tfm   = tfm;
  78         desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
  79
  80         ret = crypto_shash_init(desc);
  81         if (ret < 0)
  82                 goto error;
  83
  84         ret = crypto_shash_finup(desc, mod, modlen, pks->digest);
  85         if (ret < 0)
  86                 goto error;
  87
  88         crypto_free_shash(tfm);
  89         pr_devel("<==%s() = ok\n", __func__);
  90         return pks;
  91
  92 error:
  93         kfree(pks);
  94 error_no_pks:
  95         crypto_free_shash(tfm);
  96         pr_devel("<==%s() = %d\n", __func__, ret);
  97         return ERR_PTR(ret);
  98 }
  99
 100 /*
 101  * Extract an MPI array from the signature data.  This represents the actual
 102  * signature.  Each raw MPI is prefaced by a BE 2-byte value indicating the
 103  * size of the MPI in bytes.
 104  *
 105  * RSA signatures only have one MPI, so currently we only read one.
 106  */
 107 static int mod_extract_mpi_array(struct public_key_signature *pks,
 108                                  const void *data, size_t len)
 109 {
 110         size_t nbytes;
 111         MPI mpi;
 112
 113         if (len < 3)
 114                 return -EBADMSG;
 115         nbytes = ((const u8 *)data)[0] << 8 | ((const u8 *)data)[1];
 116         data += 2;
 117         len -= 2;
 118         if (len != nbytes)
 119                 return -EBADMSG;
 120
 121         mpi = mpi_read_raw_data(data, nbytes);
 122         if (!mpi)
 123                 return -ENOMEM;
 124         pks->mpi[0] = mpi;
 125         pks->nr_mpi = 1;
 126         return 0;
 127 }
 128
 129 /*
 130  * Request an asymmetric key.
 131  */
 132 static struct key *request_asymmetric_key(const char *signer, size_t signer_len,
 133                                           const u8 *key_id, size_t key_id_len)
 134 {
 135         key_ref_t key;
 136         size_t i;
 137         char *id, *q;
 138
 139         pr_devel("==>%s(,%zu,,%zu)\n", __func__, signer_len, key_id_len);
 140
 141         /* Construct an identifier. */
 142         id = kmalloc(signer_len + 2 + key_id_len * 2 + 1, GFP_KERNEL);
 143         if (!id)
 144                 return ERR_PTR(-ENOKEY);
 145
 146         memcpy(id, signer, signer_len);
 147
 148         q = id + signer_len;
 149         *q++ = ':';
 150         *q++ = ' ';
 151         for (i = 0; i < key_id_len; i++) {
 152                 *q++ = hex_asc[*key_id >> 4];
 153                 *q++ = hex_asc[*key_id++ & 0x0f];
 154         }
 155
 156         *q = 0;
 157
 158         pr_debug("Look up: \"%s\"\n", id);
 159
 160         key = keyring_search(make_key_ref(modsign_keyring, 1),
 161                              &key_type_asymmetric, id);
 162         if (IS_ERR(key))
 163                 pr_warn("Request for unknown module key '%s' err %ld\n",
 164                         id, PTR_ERR(key));
 165         kfree(id);
 166
 167         if (IS_ERR(key)) {
 168                 switch (PTR_ERR(key)) {
 169                         /* Hide some search errors */
 170                 case -EACCES:
 171                 case -ENOTDIR:
 172                 case -EAGAIN:
 173                         return ERR_PTR(-ENOKEY);
 174                 default:
 175                         return ERR_CAST(key);
 176                 }
 177         }
 178
 179         pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key_ref_to_ptr(key)));
 180         return key_ref_to_ptr(key);
 181 }
 182
 183 /*
 184  * Verify the signature on a module.
 185  */
 186 int mod_verify_sig(const void *mod, unsigned long *_modlen)
 187 {
 188         struct public_key_signature *pks;
 189         struct module_signature ms;
 190         struct key *key;
 191         const void *sig;
 192         size_t modlen = *_modlen, sig_len;
 193         int ret;
 194
 195         pr_devel("==>%s(,%zu)\n", __func__, modlen);
 196
 197         if (modlen <= sizeof(ms))
 198                 return -EBADMSG;
 199
 200         memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
 201         modlen -= sizeof(ms);
 202
 203         sig_len = be32_to_cpu(ms.sig_len);
 204         if (sig_len >= modlen)
 205                 return -EBADMSG;
 206         modlen -= sig_len;
 207         if ((size_t)ms.signer_len + ms.key_id_len >= modlen)
 208                 return -EBADMSG;
 209         modlen -= (size_t)ms.signer_len + ms.key_id_len;
 210
 211         *_modlen = modlen;
 212         sig = mod + modlen;
 213
 214         /* For the moment, only support RSA and X.509 identifiers */
 215         if (ms.algo != PKEY_ALGO_RSA ||
 216             ms.id_type != PKEY_ID_X509)
 217                 return -ENOPKG;
 218
 219         if (ms.hash >= PKEY_HASH__LAST ||
 220             !pkey_hash_algo[ms.hash])
 221                 return -ENOPKG;
 222
 223         key = request_asymmetric_key(sig, ms.signer_len,
 224                                      sig + ms.signer_len, ms.key_id_len);
 225         if (IS_ERR(key))
 226                 return PTR_ERR(key);
 227
 228         pks = mod_make_digest(ms.hash, mod, modlen);
 229         if (IS_ERR(pks)) {
 230                 ret = PTR_ERR(pks);
 231                 goto error_put_key;
 232         }
 233
 234         ret = mod_extract_mpi_array(pks, sig + ms.signer_len + ms.key_id_len,
 235                                     sig_len);
 236         if (ret < 0)
 237                 goto error_free_pks;
 238
 239         ret = verify_signature(key, pks);
 240         pr_devel("verify_signature() = %d\n", ret);
 241
 242 error_free_pks:
 243         mpi_free(pks->rsa.s);
 244         kfree(pks);
 245 error_put_key:
 246         key_put(key);
 247         pr_devel("<==%s() = %d\n", __func__, ret);
 248         return ret;
 249 }