From d7cde286daad20dd171247ea47fc5ff4868591f0 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Fri, 26 Sep 2014 11:35:42 +0200 Subject: [PATCH] netfilter: conntrack: disable generic tracking for known protocols commit db29a9508a9246e77087c5531e45b2c88ec6988b upstream. Given following iptables ruleset: -P FORWARD DROP -A FORWARD -m sctp --dport 9 -j ACCEPT -A FORWARD -p tcp --dport 80 -j ACCEPT -A FORWARD -p tcp -m conntrack -m state ESTABLISHED,RELATED -j ACCEPT One would assume that this allows SCTP on port 9 and TCP on port 80. Unfortunately, if the SCTP conntrack module is not loaded, this allows *all* SCTP communication, to pass though, i.e. -p sctp -j ACCEPT, which we think is a security issue. This is because on the first SCTP packet on port 9, we create a dummy "generic l4" conntrack entry without any port information (since conntrack doesn't know how to extract this information). All subsequent packets that are unknown will then be in established state since they will fallback to proto_generic and will match the 'generic' entry. Our originally proposed version [1] completely disabled generic protocol tracking, but Jozsef suggests to not track protocols for which a more suitable helper is available, hence we now mitigate the issue for in tree known ct protocol helpers only, so that at least NAT and direction information will still be preserved for others. [1] http://www.spinics.net/lists/netfilter-devel/msg33430.html Joint work with Daniel Borkmann. Signed-off-by: Florian Westphal Signed-off-by: Daniel Borkmann Acked-by: Jozsef Kadlecsik Signed-off-by: Pablo Neira Ayuso [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- Reading git-format-patch failed