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Linux/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 <linux/verification.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 verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
 84                                       NULL, VERIFYING_MODULE_SIGNATURE,
 85                                       NULL, NULL);
 86 }
 87 

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