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