passt, tap: Process data on the socket before HUP/ERR events

In the case where the client writes a packet and then closes the
socket, because we receive EPOLLIN|EPOLLRDHUP together we have a
choice of whether to close the socket immediately, or read the packet
and then close the socket.  Choose the latter.

This should improve fuzzing coverage and arguably is a better choice
even for regular use since dropping packets on close is bad.

See-also: https://archives.passt.top/passt-dev/20221117171805.3746f53a@elisabeth/
Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/tap.c b/tap.c
index 2cfd82b..2e603ed 100644
--- a/tap.c
+++ b/tap.c
@@ -1106,13 +1106,13 @@ void tap_handler(struct ctx *c, int fd, uint32_t events,
 		return;
 	}
 
-	if (events & (EPOLLRDHUP | EPOLLHUP | EPOLLERR))
-		goto reinit;
-
 	if ((c->mode == MODE_PASST && tap_handler_passt(c, now)) ||
 	    (c->mode == MODE_PASTA && tap_handler_pasta(c, now)))
 		goto reinit;
 
+	if (events & (EPOLLRDHUP | EPOLLHUP | EPOLLERR))
+		goto reinit;
+
 	return;
 reinit:
 	if (c->one_off) {