diff options
| author | Jesper Dangaard Brouer <brouer@redhat.com> | 2015-05-07 14:54:16 +0200 |
|---|---|---|
| committer | Pablo Neira Ayuso <pablo@netfilter.org> | 2015-05-15 20:50:56 +0200 |
| commit | b3cad287d13b5f6695c6b4aab72969cd64bf0171 (patch) | |
| tree | 35cb16bad9e76c3cf30e01e71b4ea5031de0a564 /include | |
| parent | 595ca5880b37d4aa3c292d75531577175d36b225 (diff) | |
conntrack: RFC5961 challenge ACK confuse conntrack LAST-ACK transition
In compliance with RFC5961, the network stack send challenge ACK in
response to spurious SYN packets, since commit 0c228e833c88 ("tcp:
Restore RFC5961-compliant behavior for SYN packets").
This pose a problem for netfilter conntrack in state LAST_ACK, because
this challenge ACK is (falsely) seen as ACKing last FIN, causing a
false state transition (into TIME_WAIT).
The challenge ACK is hard to distinguish from real last ACK. Thus,
solution introduce a flag that tracks the potential for seeing a
challenge ACK, in case a SYN packet is let through and current state
is LAST_ACK.
When conntrack transition LAST_ACK to TIME_WAIT happens, this flag is
used for determining if we are expecting a challenge ACK.
Scapy based reproducer script avail here:
https://github.com/netoptimizer/network-testing/blob/master/scapy/tcp_hacks_3WHS_LAST_ACK.py
Fixes: 0c228e833c88 ("tcp: Restore RFC5961-compliant behavior for SYN packets")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/uapi/linux/netfilter/nf_conntrack_tcp.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/include/uapi/linux/netfilter/nf_conntrack_tcp.h b/include/uapi/linux/netfilter/nf_conntrack_tcp.h index 9993a421201c..ef9f80f0f529 100644 --- a/include/uapi/linux/netfilter/nf_conntrack_tcp.h +++ b/include/uapi/linux/netfilter/nf_conntrack_tcp.h @@ -42,6 +42,9 @@ enum tcp_conntrack { /* The field td_maxack has been set */ #define IP_CT_TCP_FLAG_MAXACK_SET 0x20 +/* Marks possibility for expected RFC5961 challenge ACK */ +#define IP_CT_EXP_CHALLENGE_ACK 0x40 + struct nf_ct_tcp_flags { __u8 flags; __u8 mask; |