udp_tap_handler() currently skips outbound packets if they have a payload length of zero. This is not correct, since in a datagram protocol zero length packets still have meaning. Adjust this to correctly forward the zero-length packets by using a msghdr with msg_iovlen == 0. Bugzilla: https://bugs.passt.top/show_bug.cgi?id=19 Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au> --- udp.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/udp.c b/udp.c index c4ebecc..caa852a 100644 --- a/udp.c +++ b/udp.c @@ -1075,19 +1075,19 @@ int udp_tap_handler(struct ctx *c, int af, const void *addr, uh_send = packet_get(p, i, 0, sizeof(*uh), &len); if (!uh_send) return p->count; + + mm[i].msg_hdr.msg_name = sa; + mm[i].msg_hdr.msg_namelen = sl; + count++; + if (!len) continue; m[i].iov_base = (char *)(uh_send + 1); m[i].iov_len = len; - mm[i].msg_hdr.msg_name = sa; - mm[i].msg_hdr.msg_namelen = sl; - mm[i].msg_hdr.msg_iov = m + i; mm[i].msg_hdr.msg_iovlen = 1; - - count++; } count = sendmmsg(s, mm, count, MSG_NOSIGNAL); -- 2.37.3