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netfilter: Validate the sequence number of dataless ACK packets as well 

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@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Jozsef Kadlecsik 2012-08-31 09:55:54 +00:00 committed by Pablo Neira Ayuso
parent 64f509ce71
commit 4a70bbfaef
1 changed files with 2 additions and 8 deletions
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10
net/netfilter/nf_conntrack_proto_tcp.c
View File

@ -630,15 +630,9 @@ 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;