Patch "netfilter: nf_ct_helper: warn when not applying default helper assignment" has been added to the 4.9-stable tree

Patch "netfilter: nf_ct_helper: warn when not applying default helper assignment" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    netfilter: nf_ct_helper: warn when not applying default helper assignment

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     netfilter-nf_ct_helper-warn-when-not-applying-default-helper-assignment.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From dfe75ff8ca74f54b0fa5a326a1aa9afa485ed802 Mon Sep 17 00:00:00 2001
From: Jiri Kosina <jkosina@suse.cz>
Date: Wed, 1 Feb 2017 21:01:54 +0100
Subject: netfilter: nf_ct_helper: warn when not applying default helper assignment

From: Jiri Kosina <jkosina@suse.cz>

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 <jkosina@suse.cz>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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) {


Patches currently in stable-queue which might be from jkosina@suse.cz are

queue-4.9/netfilter-nf_ct_helper-warn-when-not-applying-default-helper-assignment.patch