virtio_net: check return value of skb_to_sgvec in one more location

BugLink: http://bugs.launchpad.net/bugs/1765010

Kernels that do not have f6b10209 ("virtio-net: switch to use
build_skb() for small buffer") will have an extra call to skb_to_sgvec
that is not handled by e2fcad58 ("virtio_net: check return value of
skb_to_sgvec always"). Since the former does not appear to be stable
material, just fix the call up directly.

Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

drivers/net/virtio_net.c

@@ -560,7 +560,12 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
 	hdr = skb_vnet_hdr(skb);
 	sg_init_table(rq->sg, 2);
 	sg_set_buf(rq->sg, hdr, vi->hdr_len);
-	skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
+
+	err = skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
+	if (unlikely(err < 0)) {
+		dev_kfree_skb(skb);
+		return err;
+	}
 
 	err = virtqueue_add_inbuf(rq->vq, rq->sg, 2, skb, gfp);
 	if (err < 0)