linux-kernel - [ 21/89] netfilter: Mark SYN/ACK packets as invalid from original direction

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Message-Id: <20121203143150.250471629@decadent.org.uk>
Date:	Mon, 03 Dec 2012 14:32:07 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	Pablo Neira Ayuso <pablo@...filter.org>
Subject: [ 21/89] netfilter: Mark SYN/ACK packets as invalid  from original direction

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>

commit 64f509ce71b08d037998e93dd51180c19b2f464c upstream.

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 <kadlec@...ckhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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 37bf943..1eb458c 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -159,21 +159,18 @@ 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 },


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