Hi Florian,
You wrote on Fri, Jul 12, 2019 at 12:29:05AM +0200:
> Jakub Jankowski reported following oddity:
>
> After 3 way handshake completes, timeout of new connection is set to
> max_retrans (300s) instead of established (5 days).
>
> shortened excerpt from pcap provided:
> 25.070622 IP (flags [DF], proto TCP (6), length 52)
> 10.8.5.4.1025 > 10.8.1.2.80: Flags [S], seq 11, win 64240, [wscale 8]
> 26.070462 IP (flags [DF], proto TCP (6), length 48)
> 10.8.1.2.80 > 10.8.5.4.1025: Flags [S.], seq 82, ack 12, win 65535, [wscale 3]
> 27.070449 IP (flags [DF], proto TCP (6), length 40)
> 10.8.5.4.1025 > 10.8.1.2.80: Flags [.], ack 83, win 512, length 0
>
> Turns out the last_win is of u16 type, but we store the scaled value:
> 512 << 8 (== 0x20000) becomes 0 window.
>
> The Fixes tag is not correct, as the bug has existed forever, but
> without that change all that this causes might cause is to mistake a
> window update (to-nonzero-from-zero) for a retransmit.
>
> Fixes: fbcd253d2448b8 ("netfilter: conntrack: lower timeout to RETRANS seconds if window is 0")
> Reported-by: Jakub Jankowski <shasta@xxxxxxxxxxx>
> Tested-by: Jakub Jankowski <shasta@xxxxxxxxxxx>
> Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
it seems the patch fixed a kernel bugzilla entry, too:
https://bugzilla.kernel.org/show_bug.cgi?id=202287
I had a feeling it could be related since the reporter bisected it
down to changes in the TCP window scaling defaults.
Cheers,
Thomas
