Re: [PATCH v4 4/8] tcp: Fix closing logic for half-closed connections

On 2025-09-09 14:16, Stefano Brivio wrote:

First off, don't close connections half-closed by the guest before our own FIN is acknowledged by the guest itself.

That is, after we receive a FIN from the guest (TAP_FIN_RCVD), if we don't have any data left to send from the socket (SOCK_FIN_RCVD, or EPOLLHUP), we send a FIN segment to the guest (TAP_FIN_SENT), but we need to actually have it acknowledged (and have no pending retransmissions) before we can close the connection: check for TAP_FIN_ACKED, first.

Then, if we set TAP_FIN_SENT, and we receive an ACK segment from the guest, set TAP_FIN_ACKED. This was entirely missing for the TAP_FIN_RCVD case, and as we fix the problem described above, this becomes relevant as well.

Signed-off-by: Stefano Brivio Reviewed-by: David Gibson

Reviewed-by: Jon Maloy

--- tcp.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/tcp.c b/tcp.c index 12d42e0..b83510b 100644 --- a/tcp.c +++ b/tcp.c @@ -2116,9 +2116,14 @@ int tcp_tap_handler(const struct ctx *c, uint8_t pif, sa_family_t af, tcp_tap_window_update(c, 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) - conn_event(c, conn, CLOSED); + if (conn->seq_ack_from_tap == conn->seq_to_tap) { + if (th->ack && conn->events & TAP_FIN_SENT) + conn_event(c, conn, TAP_FIN_ACKED); + + if (conn->events & SOCK_FIN_RCVD && + conn->events & TAP_FIN_ACKED) + conn_event(c, conn, CLOSED); + }

return 1; } @@ -2398,7 +2403,7 @@ void tcp_sock_handler(const struct ctx *c, union epoll_ref ref, return; }

- if ((conn->events & TAP_FIN_SENT) && (events & EPOLLHUP)) { + if ((conn->events & TAP_FIN_ACKED) && (events & EPOLLHUP)) { conn_event(c, conn, CLOSED); return; }