From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932747AbcAHSdk (ORCPT ); Fri, 8 Jan 2016 13:33:40 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45849 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932721AbcAHSdh (ORCPT ); Fri, 8 Jan 2016 13:33:37 -0500 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 Subject: [RFC PATCH 02/15] X.509: Don't treat self-signed keys specially From: David Howells To: zohar@linux.vnet.ibm.com Cc: dhowells@redhat.com, linux-security-module@vger.kernel.org, keyrings@vger.kernel.org, petkan@mip-labs.com, linux-kernel@vger.kernel.org Date: Fri, 08 Jan 2016 18:33:35 +0000 Message-ID: <20160108183335.25960.5138.stgit@warthog.procyon.org.uk> In-Reply-To: <20160108183319.25960.49807.stgit@warthog.procyon.org.uk> References: <20160108183319.25960.49807.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Trust for a self-signed certificate can normally only be determined by whether we obtained it from a trusted location (ie. it was built into the kernel at compile time), so there's not really any point in checking it - we could verify that the signature is valid, but it doesn't really tell us anything if the signature checks out. However, there's a bug in the code determining whether a certificate is self-signed or not - if they have neither AKID nor SKID then we just assume that the cert is self-signed, which may not be true. Given this, remove the code that treats self-signed certs specially when it comes to evaluating trustability and attempt to evaluate them as ordinary signed certificates. We then expect self-signed certificates to fail the trustability check and be marked as untrustworthy in x509_key_preparse(). Note that there is the possibility of the trustability check on a self-signed cert then succeeding. This is most likely to happen when a duplicate of the certificate is already on the trust keyring - in which case it shouldn't be a problem. Signed-off-by: David Howells cc: David Woodhouse cc: Mimi Zohar --- crypto/asymmetric_keys/x509_public_key.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c index 2a44b3752471..25455567ac06 100644 --- a/crypto/asymmetric_keys/x509_public_key.c +++ b/crypto/asymmetric_keys/x509_public_key.c @@ -255,6 +255,9 @@ static int x509_validate_trust(struct x509_certificate *cert, struct key *key; int ret = 1; + if (!cert->akid_id && !cert->akid_skid) + return 1; + if (!trust_keyring) return -EOPNOTSUPP; @@ -312,17 +315,21 @@ static int x509_key_preparse(struct key_preparsed_payload *prep) cert->pub->algo = pkey_algo[cert->pub->pkey_algo]; cert->pub->id_type = PKEY_ID_X509; - /* Check the signature on the key if it appears to be self-signed */ - if ((!cert->akid_skid && !cert->akid_id) || - asymmetric_key_id_same(cert->skid, cert->akid_skid) || - asymmetric_key_id_same(cert->id, cert->akid_id)) { - ret = x509_check_signature(cert->pub, cert); /* self-signed */ - if (ret < 0) - goto error_free_cert; - } else if (!prep->trusted) { + /* See if we can derive the trustability of this certificate. + * + * When it comes to self-signed certificates, we cannot evaluate + * trustedness except by the fact that we obtained it from a trusted + * location. So we just rely on x509_validate_trust() failing in this + * case. + * + * Note that there's a possibility of a self-signed cert matching a + * cert that we have (most likely a duplicate that we already trust) - + * in which case it will be marked trusted. + */ + if (!prep->trusted) { ret = x509_validate_trust(cert, get_system_trusted_keyring()); if (!ret) - prep->trusted = 1; + prep->trusted = true; } /* Propose a description */