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authorJozsef Kadlecsik <kadlec@blackhole.kfki.hu>2012-08-31 13:55:53 +0400
committerPablo Neira Ayuso <pablo@netfilter.org>2012-09-10 00:13:30 +0400
commit64f509ce71b08d037998e93dd51180c19b2f464c (patch)
tree3ccafa55245faaa0580e86f705548bbfe6cf3108 /net
parent0626af3139572610b56376580d11eb65d45d9dd7 (diff)
downloadlinux-64f509ce71b08d037998e93dd51180c19b2f464c.tar.xz
netfilter: Mark SYN/ACK packets as invalid from original direction
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@blackhole.kfki.hu> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'net')
-rw-r--r--net/netfilter/nf_conntrack_proto_tcp.c19
1 files changed, 8 insertions, 11 deletions
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index a5ac11ebef33..aba98f942979 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 },