From 75e4364f67d9cb996f9a6ff982ad9b3700648591 Mon Sep 17 00:00:00 2001
From: damuzi000 <damuzi000@gmail.com>
Date: Fri, 17 Jan 2014 23:47:59 +0800
Subject: [PATCH] net: stmmac: fix NULL pointer dereference in
 stmmac_get_tx_hwtstamp

When timestamping is enabled, stmmac_tx_clean will call
stmmac_get_tx_hwtstamp to get tx TS.
But the skb can be NULL because the last of its tx_skbuff is NULL
if this packet frame is filled in more than one descriptors.

To fix the issue, change the code:
- Store TX skb to the tx_skbuff[] of frame's last segment.
- Check skb is not NULL in stmmac_get_tx_hwtstamp.

Signed-off-by: Bruce Liu <damuzi000@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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