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

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 <redacted>
---
  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 670cc15..204eedf 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;
  	}