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/errno.h>
  14 #include <linux/string.h>
  15 #include <keys/system_keyring.h>
  16 #include <crypto/public_key.h>
  17 #include "module-internal.h"
  18
  19 enum pkey_id_type {
  20         PKEY_ID_PGP,            /* OpenPGP generated key ID */
  21         PKEY_ID_X509,           /* X.509 arbitrary subjectKeyIdentifier */
  22         PKEY_ID_PKCS7,          /* Signature in PKCS#7 message */
  23 };
  24
  25 /*
  26  * Module signature information block.
  27  *
  28  * The constituents of the signature section are, in order:
  29  *
  30  *      - Signer's name
  31  *      - Key identifier
  32  *      - Signature data
  33  *      - Information block
  34  */
  35 struct module_signature {
  36         u8      algo;           /* Public-key crypto algorithm [0] */
  37         u8      hash;           /* Digest algorithm [0] */
  38         u8      id_type;        /* Key identifier type [PKEY_ID_PKCS7] */
  39         u8      signer_len;     /* Length of signer's name [0] */
  40         u8      key_id_len;     /* Length of key identifier [0] */
  41         u8      __pad[3];
  42         __be32  sig_len;        /* Length of signature data */
  43 };
  44
  45 /*
  46  * Verify the signature on a module.
  47  */
  48 int mod_verify_sig(const void *mod, unsigned long *_modlen)
  49 {
  50         struct module_signature ms;
  51         size_t modlen = *_modlen, sig_len;
  52
  53         pr_devel("==>%s(,%zu)\n", __func__, modlen);
  54
  55         if (modlen <= sizeof(ms))
  56                 return -EBADMSG;
  57
  58         memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
  59         modlen -= sizeof(ms);
  60
  61         sig_len = be32_to_cpu(ms.sig_len);
  62         if (sig_len >= modlen)
  63                 return -EBADMSG;
  64         modlen -= sig_len;
  65         *_modlen = modlen;
  66
  67         if (ms.id_type != PKEY_ID_PKCS7) {
  68                 pr_err("Module is not signed with expected PKCS#7 message\n");
  69                 return -ENOPKG;
  70         }
  71
  72         if (ms.algo != 0 ||
  73             ms.hash != 0 ||
  74             ms.signer_len != 0 ||
  75             ms.key_id_len != 0 ||
  76             ms.__pad[0] != 0 ||
  77             ms.__pad[1] != 0 ||
  78             ms.__pad[2] != 0) {
  79                 pr_err("PKCS#7 signature info has unexpected non-zero params\n");
  80                 return -EBADMSG;
  81         }
  82
  83         return system_verify_data(mod, modlen, mod + modlen, sig_len,
  84                                   VERIFYING_MODULE_SIGNATURE);
  85 }