[PATCH v2 1/2] tcp_vu: vu_pad() expects l2 length

[Laurent Vivier <lvivier@redhat.com>]

tcp_vu_hdrlen() returns a length that includes VNET_HLEN (the virtio
net header), but vu_pad() expects the Layer-2 frame length, which
should not include the virtio header. Passing the inflated length
means short frames aren't padded to the minimum 60-byte Ethernet
frame size (ETH_ZLEN).

Subtract VNET_HLEN from hdrlen when computing the l2 length passed
to vu_pad() in both tcp_vu_send_flag() and tcp_vu_data_from_sock().

Fixes: 0cb8f9003654 ("tcp, udp: Pad batched frames for vhost-user modes to 60 bytes (802.3 minimum)")
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 tcp_vu.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/tcp_vu.c b/tcp_vu.c
index 3847a4e92087..2c9ddba0c9a4 100644
--- a/tcp_vu.c
+++ b/tcp_vu.c
@@ -71,8 +71,8 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags)
 {
 	struct vu_dev *vdev = c->vdev;
 	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
-	size_t optlen, hdrlen;
 	struct vu_virtq_element flags_elem[2];
+	size_t optlen, hdrlen, l2len;
 	struct ipv6hdr *ip6h = NULL;
 	struct iphdr *ip4h = NULL;
 	struct iovec flags_iov[2];
@@ -137,7 +137,8 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags)
 	tcp_fill_headers(c, conn, eh, ip4h, ip6h, th, &payload,
 			 NULL, seq, !*c->pcap);
 
-	vu_pad(&flags_elem[0].in_sg[0], hdrlen + optlen);
+	l2len = optlen + hdrlen - VNET_HLEN;
+	vu_pad(&flags_elem[0].in_sg[0], l2len);
 
 	if (*c->pcap)
 		pcap_iov(&flags_elem[0].in_sg[0], 1, VNET_HLEN);
@@ -446,6 +447,7 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn)
 		int buf_cnt = head[i + 1] - head[i];
 		ssize_t dlen = iov_size(iov, buf_cnt) - hdrlen;
 		bool push = i == head_cnt - 1;
+		size_t l2len;
 
 		vu_set_vnethdr(vdev, iov->iov_base, buf_cnt);
 
@@ -457,7 +459,8 @@ int tcp_vu_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn)
 		tcp_vu_prepare(c, conn, iov, buf_cnt, &check, !*c->pcap, push);
 
 		/* Pad first/single buffer only, it's at least ETH_ZLEN long */
-		vu_pad(iov, dlen + hdrlen);
+		l2len = dlen + hdrlen - VNET_HLEN;
+		vu_pad(iov, l2len);
 
 		if (*c->pcap)
 			pcap_iov(iov, buf_cnt, VNET_HLEN);
-- 
2.53.0