Messages in this thread | | | From | Eric Dumazet <> | Date | Mon, 25 Oct 2021 09:13:32 -0700 | Subject | Re: [net-next v1] tcp: don't free a FIN sk_buff in tcp_remove_empty_skb() |
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On Sun, Oct 24, 2021 at 4:59 PM Jon Maxwell <jmaxwell37@gmail.com> wrote: > > v1: Implement a more general statement as recommended by Eric Dumazet. The > sequence number will be advanced, so this check will fix the FIN case and > other cases. > > A customer reported sockets stuck in the CLOSING state. A Vmcore revealed that > the write_queue was not empty as determined by tcp_write_queue_empty() but the > sk_buff containing the FIN flag had been freed and the socket was zombied in > that state. Corresponding pcaps show no FIN from the Linux kernel on the wire. > > Some instrumentation was added to the kernel and it was found that there is a > timing window where tcp_sendmsg() can run after tcp_send_fin(). > > tcp_sendmsg() will hit an error, for example: > > 1269 ▹ if (sk->sk_err || (sk->sk_shutdown & SEND_SHUTDOWN))↩ > 1270 ▹ ▹ goto do_error;↩ > > tcp_remove_empty_skb() will then free the FIN sk_buff as "skb->len == 0". The > TCP socket is now wedged in the FIN-WAIT-1 state because the FIN is never sent. > > If the other side sends a FIN packet the socket will transition to CLOSING and > remain that way until the system is rebooted. > > Fix this by checking for the FIN flag in the sk_buff and don't free it if that > is the case. Testing confirmed that fixed the issue. > > Fixes: fdfc5c8594c2 ("tcp: remove empty skb from write queue in error cases") > Signed-off-by: Jon Maxwell <jmaxwell37@gmail.com> > Reported-by: Monir Zouaoui <Monir.Zouaoui@mail.schwarz> > Reported-by: Simon Stier <simon.stier@mail.schwarz>
Thanks for this fix ! Reviewed-by: Eric Dumazet <edumazet@google.com>
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