asix: Add rx->ax_skb = NULL after usbnet_skb_return()

In asix_rx_fixup_internal() there is a risk that rx->ax_skb gets
reused after passing the Ethernet frame into the network stack via
usbnet_skb_return().

The risks include:

a) asynchronously freeing rx->ax_skb after passing the netdev buffer
   to the NAPI layer which might corrupt the backlog queue.

b) erroneously reusing rx->ax_skb such as calling skb_put_data() multiple
   times which causes writing off the end of the netdev buffer.

Therefore add a defensive rx->ax_skb = NULL after usbnet_skb_return()
so that it is not possible to free rx->ax_skb or to apply
skb_put_data() too many times.

Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
index 7847436c441e..6983b6bd8cf9 100644
--- a/drivers/net/usb/asix_common.c
+++ b/drivers/net/usb/asix_common.c
@@ -168,8 +168,10 @@ int asix_rx_fixup_internal(struct usbnet *dev, struct sk_buff *skb,
                 if (rx->ax_skb) {
                         skb_put_data(rx->ax_skb, skb->data + offset,
                                      copy_length);
-                        if (!rx->remaining)
+                        if (!rx->remaining) {
                                 usbnet_skb_return(dev, rx->ax_skb);
+                                rx->ax_skb = NULL;
+                        }
                 }
 
                 offset += (copy_length + 1) & 0xfffe;