[PATCH 4.16 41/48] virtio-net: correctly check num_buf during err path

[Greg Kroah-Hartman]

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Wang <jasowang@xxxxxxxxxx>

[ Upstream commit 850e088d5bbb333342fd4def08d0a4035f2b7126 ]

If we successfully linearize the packet, num_buf will be set to zero
which may confuse error handling path which assumes num_buf is at
least 1 and this can lead the code tries to pop the descriptor of next
buffer. Fixing this by checking num_buf against 1 before decreasing.

Fixes: 4941d472bf95 ("virtio-net: do not reset during XDP set")
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/virtio_net.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -874,7 +874,7 @@ err_xdp:
 	rcu_read_unlock();
 err_skb:
 	put_page(page);
-	while (--num_buf) {
+	while (num_buf-- > 1) {
 		buf = virtqueue_get_buf(rq->vq, &len);
 		if (unlikely(!buf)) {
 			pr_debug("%s: rx error: %d buffers missing\n",