netdev - [net PATCH 2/4] virtio_net: fix XDP code path in receive

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Date:   Tue, 20 Feb 2018 14:32:10 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: [net PATCH 2/4] virtio_net: fix XDP code path in receive_small()

When configuring virtio_net to use the code path 'receive_small()',
in-order to get correct XDP_REDIRECT support, I discovered TCP packets
would get silently dropped when loading an XDP program action XDP_PASS.

The bug seems to be that receive_small() when XDP is loaded check that
hdr->hdr.flags is zero, which seems wrong as hdr.flags contains the
flags VIRTIO_NET_HDR_F_* :
 #define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 /* Use csum_start, csum_offset */
 #define VIRTIO_NET_HDR_F_DATA_VALID 2 /* Csum is valid */

TCP got dropped as it had the VIRTIO_NET_HDR_F_DATA_VALID flag set.

The flags that are relevant here are the VIRTIO_NET_HDR_GSO_* flags
stored in hdr->hdr.gso_type. Thus, the fix is just check that none of
the gso_type flags have been set.

Fixes: bb91accf2733 ("virtio-net: XDP support for small buffers")
Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 drivers/net/virtio_net.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0ca91942a884..10c8fc46b588 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -558,7 +558,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
 		void *orig_data;
 		u32 act;
 
-		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
+		if (unlikely(hdr->hdr.gso_type))
 			goto err_xdp;
 
 		if (unlikely(xdp_headroom < virtnet_get_headroom(vi))) {