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/* Verify the signature on a PKCS#7 message.
*
* Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#define pr_fmt(fmt) "PKCS7: "fmt
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/asn1.h>
#include <crypto/hash.h>
#include "public_key.h"
#include "pkcs7_parser.h"
/*
* Digest the relevant parts of the PKCS#7 data
*/
static int pkcs7_digest(struct pkcs7_message *pkcs7,
struct pkcs7_signed_info *sinfo)
{
struct crypto_shash *tfm;
struct shash_desc *desc;
size_t digest_size, desc_size;
void *digest;
int ret;
kenter(",%u,%u", sinfo->index, sinfo->sig.pkey_hash_algo);
if (sinfo->sig.pkey_hash_algo >= PKEY_HASH__LAST ||
!hash_algo_name[sinfo->sig.pkey_hash_algo])
return -ENOPKG;
/* Allocate the hashing algorithm we're going to need and find out how
* big the hash operational data will be.
*/
tfm = crypto_alloc_shash(hash_algo_name[sinfo->sig.pkey_hash_algo],
0, 0);
if (IS_ERR(tfm))
return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);
desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
sinfo->sig.digest_size = digest_size = crypto_shash_digestsize(tfm);
ret = -ENOMEM;
digest = kzalloc(digest_size + desc_size, GFP_KERNEL);
if (!digest)
goto error_no_desc;
desc = digest + digest_size;
desc->tfm = tfm;
desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
/* Digest the message [RFC2315 9.3] */
ret = crypto_shash_init(desc);
if (ret < 0)
goto error;
ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len, digest);
if (ret < 0)
goto error;
pr_devel("MsgDigest = [%*ph]\n", 8, digest);
/* However, if there are authenticated attributes, there must be a
* message digest attribute amongst them which corresponds to the
* digest we just calculated.
*/
if (sinfo->msgdigest) {
u8 tag;
if (sinfo->msgdigest_len != sinfo->sig.digest_size) {
pr_debug("Sig %u: Invalid digest size (%u)\n",
sinfo->index, sinfo->msgdigest_len);
ret = -EBADMSG;
goto error;
}
if (memcmp(digest, sinfo->msgdigest, sinfo->msgdigest_len) != 0) {
pr_debug("Sig %u: Message digest doesn't match\n",
sinfo->index);
ret = -EKEYREJECTED;
goto error;
}
/* We then calculate anew, using the authenticated attributes
* as the contents of the digest instead. Note that we need to
* convert the attributes from a CONT.0 into a SET before we
* hash it.
*/
memset(digest, 0, sinfo->sig.digest_size);
ret = crypto_shash_init(desc);
if (ret < 0)
goto error;
tag = ASN1_CONS_BIT | ASN1_SET;
ret = crypto_shash_update(desc, &tag, 1);
if (ret < 0)
goto error;
ret = crypto_shash_finup(desc, sinfo->authattrs,
sinfo->authattrs_len, digest);
if (ret < 0)
goto error;
pr_devel("AADigest = [%*ph]\n", 8, digest);
}
sinfo->sig.digest = digest;
digest = NULL;
error:
kfree(digest);
error_no_desc:
crypto_free_shash(tfm);
kleave(" = %d", ret);
return ret;
}
/*
* Find the key (X.509 certificate) to use to verify a PKCS#7 message. PKCS#7
* uses the issuer's name and the issuing certificate serial number for
* matching purposes. These must match the certificate issuer's name (not
* subject's name) and the certificate serial number [RFC 2315 6.7].
*/
static int pkcs7_find_key(struct pkcs7_message *pkcs7,
struct pkcs7_signed_info *sinfo)
{
struct x509_certificate *x509;
unsigned certix = 1;
kenter("%u,%u,%u",
sinfo->index, sinfo->raw_serial_size, sinfo->raw_issuer_size);
for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
/* I'm _assuming_ that the generator of the PKCS#7 message will
* encode the fields from the X.509 cert in the same way in the
* PKCS#7 message - but I can't be 100% sure of that. It's
* possible this will need element-by-element comparison.
*/
if (x509->raw_serial_size != sinfo->raw_serial_size ||
memcmp(x509->raw_serial, sinfo->raw_serial,
sinfo->raw_serial_size) != 0)
continue;
pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
sinfo->index, certix);
if (x509->raw_issuer_size != sinfo->raw_issuer_size ||
memcmp(x509->raw_issuer, sinfo->raw_issuer,
sinfo->raw_issuer_size) != 0) {
pr_warn("Sig %u: X.509 subject and PKCS#7 issuer don't match\n",
sinfo->index);
continue;
}
if (x509->pub->pkey_algo != sinfo->sig.pkey_algo) {
pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
sinfo->index);
continue;
}
sinfo->signer = x509;
return 0;
}
pr_warn("Sig %u: Issuing X.509 cert not found (#%*ph)\n",
sinfo->index, sinfo->raw_serial_size, sinfo->raw_serial);
return -ENOKEY;
}
/*
* Verify one signed information block from a PKCS#7 message.
*/
static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
struct pkcs7_signed_info *sinfo)
{
int ret;
kenter(",%u", sinfo->index);
/* First of all, digest the data in the PKCS#7 message and the
* signed information block
*/
ret = pkcs7_digest(pkcs7, sinfo);
if (ret < 0)
return ret;
/* Find the key for the signature */
ret = pkcs7_find_key(pkcs7, sinfo);
if (ret < 0)
return ret;
pr_devel("Using X.509[%u] for sig %u\n",
sinfo->signer->index, sinfo->index);
/* Verify the PKCS#7 binary against the key */
ret = public_key_verify_signature(sinfo->signer->pub, &sinfo->sig);
if (ret < 0)
return ret;
pr_devel("Verified signature %u\n", sinfo->index);
return 0;
}
/**
* pkcs7_verify - Verify a PKCS#7 message
* @pkcs7: The PKCS#7 message to be verified
*/
int pkcs7_verify(struct pkcs7_message *pkcs7)
{
struct pkcs7_signed_info *sinfo;
struct x509_certificate *x509;
int ret, n;
kenter("");
for (n = 0, x509 = pkcs7->certs; x509; x509 = x509->next, n++) {
ret = x509_get_sig_params(x509);
if (ret < 0)
return ret;
pr_debug("X.509[%u] %s\n", n, x509->authority);
}
for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
ret = pkcs7_verify_one(pkcs7, sinfo);
if (ret < 0) {
kleave(" = %d", ret);
return ret;
}
}
kleave(" = 0");
return 0;
}
EXPORT_SYMBOL_GPL(pkcs7_verify);
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