[ 22/89] netfilter: Validate the sequence number of dataless ACK packets aswell

From: Ben Hutchings
Date: Mon Dec 03 2012 - 09:38:10 EST


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

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

From: Jozsef Kadlecsik <kadlec@xxxxxxxxxxxxxxxxx>

commit 4a70bbfaef0361d27272629d1a250a937edcafe4 upstream.

We spare nothing by not validating the sequence number of dataless
ACK packets and enabling it makes harder off-path attacks.

See: "Reflection scan: an Off-Path Attack on TCP" by Jan Wrobel,
http://arxiv.org/abs/1201.2074

Signed-off-by: Jozsef Kadlecsik <kadlec@xxxxxxxxxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
net/netfilter/nf_conntrack_proto_tcp.c | 10 ++--------
1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 1eb458c..a9d5f50 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -625,15 +625,9 @@ static bool tcp_in_window(const struct nf_conn *ct,
ack = sack = receiver->td_end;
}

- if (seq == end
- && (!tcph->rst
- || (seq == 0 && state->state == TCP_CONNTRACK_SYN_SENT)))
+ if (tcph->rst && seq == 0 && state->state == TCP_CONNTRACK_SYN_SENT)
/*
- * Packets contains no data: we assume it is valid
- * and check the ack value only.
- * However RST segments are always validated by their
- * SEQ number, except when seq == 0 (reset sent answering
- * SYN.
+ * RST sent answering SYN.
*/
seq = end = sender->td_end;



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