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linux-next/crypto/asymmetric_keys/pkcs7_trust.c
David Howells 4155942000 PKCS#7: Better handling of unsupported crypto
Provide better handling of unsupported crypto when verifying a PKCS#7 message.
If we can't bridge the gap between a pair of X.509 certs or between a signed
info block and an X.509 cert because it involves some crypto we don't support,
that's not necessarily the end of the world as there may be other ways points
at which we can intersect with a ring of trusted keys.

Instead, only produce ENOPKG immediately if all the signed info blocks in a
PKCS#7 message require unsupported crypto to bridge to the first X.509 cert.
Otherwise, we defer the generation of ENOPKG until we get ENOKEY during trust
validation.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
2014-09-16 17:36:15 +01:00

174 lines
4.3 KiB
C

/* 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 "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;
bool trusted;
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) {
trusted = x509->trusted;
goto verified;
}
kleave(" = -ENOKEY [cached]");
return -ENOKEY;
}
x509->seen = true;
/* Look to see if this certificate is present in the trusted
* keys.
*/
key = x509_request_asymmetric_key(trust_keyring, x509->id);
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.
*/
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->next == 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->issuer || !last->authority) {
kleave(" = -ENOKEY [no backref]");
return -ENOKEY;
}
key = x509_request_asymmetric_key(trust_keyring, last->authority);
if (IS_ERR(key))
return PTR_ERR(key) == -ENOMEM ? -ENOMEM : -ENOKEY;
x509 = last;
matched:
ret = verify_signature(key, sig);
trusted = test_bit(KEY_FLAG_TRUSTED, &key->flags);
key_put(key);
if (ret < 0) {
if (ret == -ENOMEM)
return ret;
kleave(" = -EKEYREJECTED [verify %d]", ret);
return -EKEYREJECTED;
}
verified:
x509->verified = true;
for (p = sinfo->signer; p != x509; p = p->signer) {
p->verified = true;
p->trusted = trusted;
}
sinfo->trusted = trusted;
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
* @_trusted: Set to true if trustworth, false otherwise
*
* 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,
bool *_trusted)
{
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:
*_trusted |= sinfo->trusted;
cached_ret = 0;
continue;
default:
return ret;
}
}
return cached_ret;
}
EXPORT_SYMBOL_GPL(pkcs7_validate_trust);