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/* Validate the trust chain of 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 <linux/key.h>
#include <keys/asymmetric-type.h>
#include <crypto/public_key.h>
#include "pkcs7_parser.h"
/**
* Check the trust on one PKCS#7 SignedInfo block.
*/
static int pkcs7_validate_trust_one(struct pkcs7_message *pkcs7,
struct pkcs7_signed_info *sinfo,
struct key *trust_keyring)
{
struct public_key_signature *sig = sinfo->sig;
struct x509_certificate *x509, *last = NULL, *p;
struct key *key;
int ret;
kenter(",%u,", sinfo->index);
if (sinfo->unsupported_crypto) {
kleave(" = -ENOPKG [cached]");
return -ENOPKG;
}
for (x509 = sinfo->signer; x509; x509 = x509->signer) {
if (x509->seen) {
if (x509->verified)
goto verified;
kleave(" = -ENOKEY [cached]");
return -ENOKEY;
}
x509->seen = true;
/* Look to see if this certificate is present in the trusted
* keys.
*/
key = find_asymmetric_key(trust_keyring,
x509->id, x509->skid, false);
if (!IS_ERR(key)) {
/* One of the X.509 certificates in the PKCS#7 message
* is apparently the same as one we already trust.
* Verify that the trusted variant can also validate
* the signature on the descendant.
*/
pr_devel("sinfo %u: Cert %u as key %x\n",
sinfo->index, x509->index, key_serial(key));
goto matched;
}
if (key == ERR_PTR(-ENOMEM))
return -ENOMEM;
/* Self-signed certificates form roots of their own, and if we
* don't know them, then we can't accept them.
*/
if (x509->signer == x509) {
kleave(" = -ENOKEY [unknown self-signed]");
return -ENOKEY;
}
might_sleep();
last = x509;
sig = last->sig;
}
/* No match - see if the root certificate has a signer amongst the
* trusted keys.
*/
if (last && (last->sig->auth_ids[0] || last->sig->auth_ids[1])) {
key = find_asymmetric_key(trust_keyring,
last->sig->auth_ids[0],
last->sig->auth_ids[1],
false);
if (!IS_ERR(key)) {
x509 = last;
pr_devel("sinfo %u: Root cert %u signer is key %x\n",
sinfo->index, x509->index, key_serial(key));
goto matched;
}
if (PTR_ERR(key) != -ENOKEY)
return PTR_ERR(key);
}
/* As a last resort, see if we have a trusted public key that matches
* the signed info directly.
*/
key = find_asymmetric_key(trust_keyring,
sinfo->sig->auth_ids[0], NULL, false);
if (!IS_ERR(key)) {
pr_devel("sinfo %u: Direct signer is key %x\n",
sinfo->index, key_serial(key));
x509 = NULL;
goto matched;
}
if (PTR_ERR(key) != -ENOKEY)
return PTR_ERR(key);
kleave(" = -ENOKEY [no backref]");
return -ENOKEY;
matched:
ret = verify_signature(key, sig);
key_put(key);
if (ret < 0) {
if (ret == -ENOMEM)
return ret;
kleave(" = -EKEYREJECTED [verify %d]", ret);
return -EKEYREJECTED;
}
verified:
if (x509) {
x509->verified = true;
for (p = sinfo->signer; p != x509; p = p->signer)
p->verified = true;
}
kleave(" = 0");
return 0;
}
/**
* pkcs7_validate_trust - Validate PKCS#7 trust chain
* @pkcs7: The PKCS#7 certificate to validate
* @trust_keyring: Signing certificates to use as starting points
*
* Validate that the certificate chain inside the PKCS#7 message intersects
* keys we already know and trust.
*
* Returns, in order of descending priority:
*
* (*) -EKEYREJECTED if a signature failed to match for which we have a valid
* key, or:
*
* (*) 0 if at least one signature chain intersects with the keys in the trust
* keyring, or:
*
* (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
* chain.
*
* (*) -ENOKEY if we couldn't find a match for any of the signature chains in
* the message.
*
* May also return -ENOMEM.
*/
int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
struct key *trust_keyring)
{
struct pkcs7_signed_info *sinfo;
struct x509_certificate *p;
int cached_ret = -ENOKEY;
int ret;
for (p = pkcs7->certs; p; p = p->next)
p->seen = false;
for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
ret = pkcs7_validate_trust_one(pkcs7, sinfo, trust_keyring);
switch (ret) {
case -ENOKEY:
continue;
case -ENOPKG:
if (cached_ret == -ENOKEY)
cached_ret = -ENOPKG;
continue;
case 0:
cached_ret = 0;
continue;
default:
return ret;
}
}
return cached_ret;
}
EXPORT_SYMBOL_GPL(pkcs7_validate_trust);
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