From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:58546 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751894AbdBXIj4 (ORCPT ); Fri, 24 Feb 2017 03:39:56 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jiri Kosina , Pablo Neira Ayuso Subject: [PATCH 4.9 28/32] netfilter: nf_ct_helper: warn when not applying default helper assignment Date: Fri, 24 Feb 2017 09:38:12 +0100 Message-Id: <20170224083750.678019405@linuxfoundation.org> In-Reply-To: <20170224083746.364657938@linuxfoundation.org> References: <20170224083746.364657938@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiri Kosina commit dfe75ff8ca74f54b0fa5a326a1aa9afa485ed802 upstream. Commit 3bb398d925 ("netfilter: nf_ct_helper: disable automatic helper assignment") is causing behavior regressions in firewalls, as traffic handled by conntrack helpers is now by default not passed through even though it was before due to missing CT targets (which were not necessary before this commit). The default had to be switched off due to security reasons [1] [2] and therefore should stay the way it is, but let's be friendly to firewall admins and issue a warning the first time we're in situation where packet would be likely passed through with the old default but we're likely going to drop it on the floor now. Rewrite the code a little bit as suggested by Linus, so that we avoid spaghettiing the code even more -- namely the whole decision making process regarding helper selection (either automatic or not) is being separated, so that the whole logic can be simplified and code (condition) duplication reduced. [1] https://cansecwest.com/csw12/conntrack-attack.pdf [2] https://home.regit.org/netfilter-en/secure-use-of-helpers/ Signed-off-by: Jiri Kosina Signed-off-by: Pablo Neira Ayuso Signed-off-by: Greg Kroah-Hartman --- net/netfilter/nf_conntrack_helper.c | 39 ++++++++++++++++++++++++------------ 1 file changed, 26 insertions(+), 13 deletions(-) --- a/net/netfilter/nf_conntrack_helper.c +++ b/net/netfilter/nf_conntrack_helper.c @@ -188,6 +188,26 @@ nf_ct_helper_ext_add(struct nf_conn *ct, } EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add); +static struct nf_conntrack_helper * +nf_ct_lookup_helper(struct nf_conn *ct, struct net *net) +{ + if (!net->ct.sysctl_auto_assign_helper) { + if (net->ct.auto_assign_helper_warned) + return NULL; + if (!__nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple)) + return NULL; + pr_info("nf_conntrack: default automatic helper assignment " + "has been turned off for security reasons and CT-based " + " firewall rule not found. Use the iptables CT target " + "to attach helpers instead.\n"); + net->ct.auto_assign_helper_warned = 1; + return NULL; + } + + return __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple); +} + + int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl, gfp_t flags) { @@ -213,21 +233,14 @@ int __nf_ct_try_assign_helper(struct nf_ } help = nfct_help(ct); - if (net->ct.sysctl_auto_assign_helper && helper == NULL) { - helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple); - if (unlikely(!net->ct.auto_assign_helper_warned && helper)) { - pr_info("nf_conntrack: automatic helper " - "assignment is deprecated and it will " - "be removed soon. Use the iptables CT target " - "to attach helpers instead.\n"); - net->ct.auto_assign_helper_warned = true; - } - } if (helper == NULL) { - if (help) - RCU_INIT_POINTER(help->helper, NULL); - return 0; + helper = nf_ct_lookup_helper(ct, net); + if (helper == NULL) { + if (help) + RCU_INIT_POINTER(help->helper, NULL); + return 0; + } } if (help == NULL) {