From mboxrd@z Thu Jan 1 00:00:00 1970 From: pablo@netfilter.org Subject: [PATCH 2/4] netfilter: Mark SYN/ACK packets as invalid from original direction Date: Thu, 13 Sep 2012 12:54:06 +0200 Message-ID: <1347533648-3451-3-git-send-email-pablo@netfilter.org> References: <1347533648-3451-1-git-send-email-pablo@netfilter.org> Cc: davem@davemloft.net, netdev@vger.kernel.org To: netfilter-devel@vger.kernel.org Return-path: In-Reply-To: <1347533648-3451-1-git-send-email-pablo@netfilter.org> Sender: netdev-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org From: Jozsef Kadlecsik Clients should not send such packets. By accepting them, we open up a hole by wich ephemeral ports can be discovered in an off-path attack. See: "Reflection scan: an Off-Path Attack on TCP" by Jan Wrobel, http://arxiv.org/abs/1201.2074 Signed-off-by: Jozsef Kadlecsik Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_proto_tcp.c | 19 ++++++++----------- 1 file changed, 8 insertions(+), 11 deletions(-) diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index a5ac11e..aba98f9 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -158,21 +158,18 @@ static const u8 tcp_conntracks[2][6][TCP_CONNTRACK_MAX] = { * sCL -> sSS */ /* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */ -/*synack*/ { sIV, sIV, sIG, sIG, sIG, sIG, sIG, sIG, sIG, sSR }, +/*synack*/ { sIV, sIV, sSR, sIV, sIV, sIV, sIV, sIV, sIV, sSR }, /* * sNO -> sIV Too late and no reason to do anything * sSS -> sIV Client can't send SYN and then SYN/ACK * sS2 -> sSR SYN/ACK sent to SYN2 in simultaneous open - * sSR -> sIG - * sES -> sIG Error: SYNs in window outside the SYN_SENT state - * are errors. Receiver will reply with RST - * and close the connection. - * Or we are not in sync and hold a dead connection. - * sFW -> sIG - * sCW -> sIG - * sLA -> sIG - * sTW -> sIG - * sCL -> sIG + * sSR -> sSR Late retransmitted SYN/ACK in simultaneous open + * sES -> sIV Invalid SYN/ACK packets sent by the client + * sFW -> sIV + * sCW -> sIV + * sLA -> sIV + * sTW -> sIV + * sCL -> sIV */ /* sNO, sSS, sSR, sES, sFW, sCW, sLA, sTW, sCL, sS2 */ /*fin*/ { sIV, sIV, sFW, sFW, sLA, sLA, sLA, sTW, sCL, sIV }, -- 1.7.10.4