From: Jesper Dangaard Brouer <brouer@redhat.com>
Date: Tue, 20 Feb 2018 13:32:10 +0000 (+0100)
Subject: virtio_net: fix XDP code path in receive_small()
X-Git-Tag: v4.16-rc3~8^2~16^2~2
X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=95dbe9e7b3720efa5cf83d21f44f6d953f7cf4a2;p=linux.git

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@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

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))) {