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