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Diffstat (limited to 'tcp.c')
-rw-r--r--tcp.c29
1 files changed, 24 insertions, 5 deletions
diff --git a/tcp.c b/tcp.c
index cb93ba3..64bf786 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1782,7 +1782,23 @@ static void tcp_clamp_window(const struct ctx *c, struct tcp_tap_conn *conn,
wnd <<= conn->ws_from_tap;
wnd = MIN(MAX_WINDOW, wnd);
- if (conn->flags & WND_CLAMPED) {
+ /* TODO: With (at least) Linux kernel versions 6.1 to 6.5, if we end up
+ * with a zero-sized window on a TCP socket, dropping data (once
+ * acknowledged by the guest) with recv() and MSG_TRUNC doesn't appear
+ * to be enough to make the kernel advertise a non-zero window to the
+ * sender. Forcing a TCP_WINDOW_CLAMP setting, even with the existing
+ * value, fixes this.
+ *
+ * The STALLED flag on a connection is a sufficient indication that we
+ * might have a zero-sized window on the socket, because it's set if we
+ * exhausted the tap-side window, or if everything we receive from a
+ * socket is already in flight to the guest.
+ *
+ * So, if STALLED is set, and we received a window value from the tap,
+ * force a TCP_WINDOW_CLAMP setsockopt(). This should be investigated
+ * further and fixed in the kernel instead, if confirmed.
+ */
+ if (!(conn->flags & STALLED) && conn->flags & WND_CLAMPED) {
if (prev_scaled == wnd)
return;
@@ -2405,12 +2421,12 @@ static int tcp_data_from_tap(struct ctx *c, struct tcp_tap_conn *conn,
i = keep - 1;
}
- tcp_clamp_window(c, conn, max_ack_seq_wnd);
-
/* On socket flush failure, pretend there was no ACK, try again later */
if (ack && !tcp_sock_consume(conn, max_ack_seq))
tcp_update_seqack_from_tap(c, conn, max_ack_seq);
+ tcp_clamp_window(c, conn, max_ack_seq_wnd);
+
if (retr) {
trace("TCP: fast re-transmit, ACK: %u, previous sequence: %u",
max_ack_seq, conn->seq_to_tap);
@@ -2568,8 +2584,6 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr,
if (th->ack && !(conn->events & ESTABLISHED))
tcp_update_seqack_from_tap(c, conn, ntohl(th->ack_seq));
- conn_flag(c, conn, ~STALLED);
-
/* Establishing connection from socket */
if (conn->events & SOCK_ACCEPTED) {
if (th->syn && th->ack && !th->fin) {
@@ -2624,6 +2638,11 @@ int tcp_tap_handler(struct ctx *c, int af, const void *saddr, const void *daddr,
if (count == -1)
goto reset;
+ /* Note: STALLED matters for tcp_clamp_window(): unset it only after
+ * processing data (and window) from the tap side
+ */
+ conn_flag(c, conn, ~STALLED);
+
if (conn->seq_ack_to_tap != conn->seq_from_tap)
ack_due = 1;