tcp_vu, udp_vu: Account for virtio net header in minimum frame size

In the vhost-user paths, the buffers provided by the virtio queue
include the virtio net header (VNET_HLEN) prepended to the Ethernet
frame. The minimum size checks using ETH_ZLEN must therefore account
for this additional header length, otherwise we underestimate the
minimum buffer size needed.

Use ETH_ZLEN + VNET_HLEN instead of bare ETH_ZLEN in vu_collect()
calls and the corresponding ASSERT() checks.

In tcp_vu_prepare(), revert the ASSERT to just check for hdrlen,
because at that point iov[0].iov_len has been trimmed to the actual
received data size plus headers.

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>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 5 insertions, 5 deletions

diff --git a/tcp_vu.c b/tcp_vu.c
index 2c9ddba..94169c2 100644
--- a/tcp_vu.c
+++ b/tcp_vu.c
@@ -90,12 +90,12 @@ int tcp_vu_send_flag(const struct ctx *c, struct tcp_tap_conn *conn, int flags)
 	vu_set_element(&flags_elem[0], NULL, &flags_iov[0]);
 
 	elem_cnt = vu_collect(vdev, vq, &flags_elem[0], 1,
-			      MAX(hdrlen + sizeof(*opts), ETH_ZLEN), NULL);
+			      MAX(hdrlen + sizeof(*opts), ETH_ZLEN + VNET_HLEN), NULL);
 	if (elem_cnt != 1)
 		return -1;
 
 	ASSERT(flags_elem[0].in_sg[0].iov_len >=
-	       MAX(hdrlen + sizeof(*opts), ETH_ZLEN));
+	       MAX(hdrlen + sizeof(*opts), ETH_ZLEN + VNET_HLEN));
 
 	vu_set_vnethdr(vdev, flags_elem[0].in_sg[0].iov_base, 1);
 
@@ -209,7 +209,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq,
 
 		cnt = vu_collect(vdev, vq, &elem[elem_cnt],
 				 VIRTQUEUE_MAX_SIZE - elem_cnt,
-				 MAX(MIN(mss, fillsize) + hdrlen, ETH_ZLEN),
+				 MAX(MIN(mss, fillsize) + hdrlen, ETH_ZLEN + VNET_HLEN),
 				 &frame_size);
 		if (cnt == 0)
 			break;
@@ -303,7 +303,7 @@ static void tcp_vu_prepare(const struct ctx *c, struct tcp_tap_conn *conn,
 	/* we guess the first iovec provided by the guest can embed
 	 * all the headers needed by L2 frame, including any padding
 	 */
-	ASSERT(iov[0].iov_len >= MAX(hdrlen, ETH_ZLEN));
+	ASSERT(iov[0].iov_len >= hdrlen);
 
 	eh = vu_eth(base);
 
diff --git a/udp_vu.c b/udp_vu.c
index 4f1eac4..d190fef 100644
--- a/udp_vu.c
+++ b/udp_vu.c
@@ -97,7 +97,7 @@ static int udp_vu_sock_recv(const struct ctx *c, struct vu_virtq *vq, int s,
 		return -1;
 
 	/* reserve space for the headers */
-	ASSERT(iov_vu[0].iov_len >= MAX(hdrlen, ETH_ZLEN));
+	ASSERT(iov_vu[0].iov_len >= MAX(hdrlen, ETH_ZLEN + VNET_HLEN));
 	iov_vu[0].iov_base = (char *)iov_vu[0].iov_base + hdrlen;
 	iov_vu[0].iov_len -= hdrlen;