Re: 2.6.12 netfilter: local packets marked as invalid

[Patrick McHardy <kaber@trash.net>]

Daniel Drake wrote:
> When retrying the telnet test, this appears in the logs:
> 
> Jul  8 14:53:04 dsd inv IN=lo OUT=
> MAC=00:00:00:00:00:00:00:00:00:00:00:00:08:00 SRC=127.0.0.1 DST=127.0.0.1
> LEN=40 TOS=0x10 PREC=0x00 TTL=64 ID=15 DF PROTO=TCP SPT=80 DPT=58950 WINDOW=0
> RES=0x00 ACK RST URGP=0
> 
> Does this mean that the kernel thinks its own ACK RST packet is invalid?

I think I know what happens. In 2.6.12 we started dropping the conntrack
reference when a packet leaves IP, so packets on loopback are tracked
twice (LOCAL_OUT/PRE_ROUTING). TCP connection tracking destroys a
conntrack entry when the only reply is an RST. So when the packet is
tracked for the second time in PRE_ROUTING, the conntrack entry can't
be found anymore and the packet is considered invalid.

You could confirm this theory by logging invalid packets in LOCAL_OUT
and in PRE_ROUTING - only PRE_ROUTING should trigger. I'm going to
think about a solution meanwhile.

Regards
Patrick