From 22889dbbd98a0e3390e9120074c39c6e5a3fea5e Mon Sep 17 00:00:00 2001
From: Dean Jenkins <Dean_Jenkins@mentor.com>
Date: Mon, 7 Aug 2017 09:50:14 +0100
Subject: [PATCH] asix: Add rx->ax_skb = NULL after usbnet_skb_return()
Git-commit: 22889dbbd98a0e3390e9120074c39c6e5a3fea5e
References: git-fixes
Patch-mainline: v4.13-rc5

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>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/net/usb/asix_common.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

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;
-- 
2.34.1