From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: passt-dev@passt.top
Subject: Re: [PATCH] tcp: Keep updating window and checking for socket data after FIN from guest
Date: Fri, 14 Feb 2025 10:01:07 +1100 [thread overview]
Message-ID: <Z655s2tRXkuiaC_H@zatzit> (raw)
In-Reply-To: <20250213221644.4086036-1-sbrivio@redhat.com>
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On Thu, Feb 13, 2025 at 11:16:44PM +0100, Stefano Brivio wrote:
> Once we get a FIN segment from the container/guest, we enter something
> resembling CLOSE_WAIT (from the perspective of the peer), but that
> doesn't mean that we should stop processing window updates from the
> guest and checking for socket data if the guest acknowledges
> something.
>
> If we don't do that, we can very easily run into a situation where we
> send a burst of data to the tap, get a zero window update, along with
> a FIN segment, because the flow is meant to be unidirectional, and now
> the connection will be stuck forever, because we'll ignore updates.
>
> Reproducer, server:
>
> $ pasta --config-net -t 9999 -- sh -c 'echo DONE | socat TCP-LISTEN:9997,shut-down STDIO'
>
> and client:
>
> $ ./test/rampstream send 50000 | socat -u STDIN TCP:$LOCAL_ADDR:9997
> 2025/02/13 09:14:45 socat[2997126] E write(5, 0x55f5dbf47000, 8192): Broken pipe
>
> while at it, update the message string for the third passive close
> state (which we see in this case): it's CLOSE_WAIT, not LAST_ACK.
>
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> ---
> tcp.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/tcp.c b/tcp.c
> index a1d6c53..16d01f6 100644
> --- a/tcp.c
> +++ b/tcp.c
> @@ -338,7 +338,7 @@ static const char *tcp_state_str[] __attribute((__unused__)) = {
> "SYN_RCVD", /* approximately maps to TAP_SYN_ACK_SENT */
>
> /* Passive close: */
> - "CLOSE_WAIT", "CLOSE_WAIT", "LAST_ACK", "LAST_ACK", "LAST_ACK",
> + "CLOSE_WAIT", "CLOSE_WAIT", "CLOSE_WAIT", "LAST_ACK", "LAST_ACK",
> /* Active close (+5): */
> "CLOSING", "FIN_WAIT_1", "FIN_WAIT_1", "FIN_WAIT_2", "TIME_WAIT",
> };
> @@ -1968,6 +1968,8 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af,
> /* Established connections not accepting data from tap */
> if (conn->events & TAP_FIN_RCVD) {
> tcp_update_seqack_from_tap(c, conn, ntohl(th->ack_seq));
> + tcp_tap_window_update(conn, ntohs(th->window));
> + tcp_data_from_sock(c, conn);
>
> if (conn->events & SOCK_FIN_RCVD &&
> conn->seq_ack_from_tap == conn->seq_to_tap)
--
David Gibson (he or they) | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you, not the other way
| around.
http://www.ozlabs.org/~dgibson
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prev parent reply other threads:[~2025-02-13 23:41 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-13 22:16 [PATCH] tcp: Keep updating window and checking for socket data after FIN from guest Stefano Brivio
2025-02-13 23:01 ` David Gibson [this message]
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