module_signing.c

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    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         u8      algo;           /* Public-key crypto algorithm [enum pkey_algo] */
   31         u8      hash;           /* Digest algorithm [enum pkey_hash_algo] */
   32         u8      id_type;        /* Key identifier type [enum pkey_id_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 }

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FreeBSD/Linux Kernel Cross Reference sys/kernel/module_signing.c

FreeBSD/Linux Kernel Cross Reference
sys/kernel/module_signing.c