From ebdd46367ce1acba235013d97e362b8677b538d5 Mon Sep 17 00:00:00 2001
From: Stefano Brivio <sbrivio@redhat.com>
Date: Wed, 19 Mar 2025 17:57:45 +0100
Subject: [PATCH] tcp: Flush socket before checking for more data in active
close state
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Otherwise, if all the pending data is acknowledged:
- tcp_update_seqack_from_tap() updates the current tap-side ACK
sequence (conn->seq_ack_from_tap)
- next, we compare the sequence we sent (conn->seq_to_tap) to the
ACK sequence (conn->seq_ack_from_tap) in tcp_data_from_sock() to
understand if there's more data we can send.
If they match, we conclude that we haven't sent any of that data,
and keep re-sending it.
We need, instead, to flush the socket (drop acknowledged data) before
calling tcp_update_seqack_from_tap(), so that once we update
conn->seq_ack_from_tap, we can be sure that all data until there is
gone from the socket.
Link: https://bugs.passt.top/show_bug.cgi?id=114
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Fixes: 30f1e082c3c0 ("tcp: Keep updating window and checking for socket data after FIN from guest")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
---
tcp.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/tcp.c b/tcp.c
index 68af43d..fa1d885 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2049,6 +2049,7 @@ 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_sock_consume(conn, ntohl(th->ack_seq));
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);