[PATCH v2 net 4/7] virtio_net: Fix out of bounds access of sq

[Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>]

When XDP is disabled, curr_queue_pairs + smp_processor_id() can be
larger than max_queue_pairs.
There is no guarantee that we have enough XDP send queues dedicated for
each cpu when XDP is disabled, so do not count drops on sq in that case.

Fixes: 5b8f3c8d30a6 ("virtio_net: Add XDP related stats")
Signed-off-by: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/net/virtio_net.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0e1a369..669b65c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -491,20 +491,17 @@ static int virtnet_xdp_xmit(struct net_device *dev,
 	int ret, err;
 	int i;
 
-	sq = virtnet_xdp_sq(vi);
-
-	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) {
-		ret = -EINVAL;
-		drops = n;
-		goto out;
-	}
-
 	/* Only allow ndo_xdp_xmit if XDP is loaded on dev, as this
 	 * indicate XDP resources have been successfully allocated.
 	 */
 	xdp_prog = rcu_dereference(rq->xdp_prog);
-	if (!xdp_prog) {
-		ret = -ENXIO;
+	if (!xdp_prog)
+		return -ENXIO;
+
+	sq = virtnet_xdp_sq(vi);
+
+	if (unlikely(flags & ~XDP_XMIT_FLAGS_MASK)) {
+		ret = -EINVAL;
 		drops = n;
 		goto out;
 	}
-- 
1.8.3.1