Re: [BACKPORT 4.4.y 18/25] tcp/dccp: drop SYN packets if accept queue is full

[Greg KH]

On Fri, Mar 22, 2019 at 04:44:09PM +0100, Arnd Bergmann wrote:
> From: Eric Dumazet <edumazet@xxxxxxxxxx>
> 
> Per listen(fd, backlog) rules, there is really no point accepting a SYN,
> sending a SYNACK, and dropping the following ACK packet if accept queue
> is full, because application is not draining accept queue fast enough.
> 
> This behavior is fooling TCP clients that believe they established a
> flow, while there is nothing at server side. They might then send about
> 10 MSS (if using IW10) that will be dropped anyway while server is under
> stress.
> 
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
> Acked-by: Yuchung Cheng <ycheng@xxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> (cherry picked from commit 5ea8ea2cb7f1d0db15762c9b0bb9e7330425a071)

Also queued up for 4.9.y