[NET]: Fix race in generic address resolution.

neigh_update sends skb from neigh->arp_queue while neigh_timer_handler
has increased skbs refcount and calls solicit with the
skb. neigh_timer_handler should not increase skbs refcount but make a
copy of the skb and do solicit with the copy.
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/neighbour.c

@@ -839,7 +839,7 @@ static void neigh_timer_handler(unsigned long arg)
 		struct sk_buff *skb = skb_peek(&neigh->arp_queue);
 		/* keep skb alive even if arp_queue overflows */
 		if (skb)
-			skb_get(skb);
+			skb = skb_copy(skb, GFP_ATOMIC);
 		write_unlock(&neigh->lock);
 		neigh->ops->solicit(neigh, skb);
 		atomic_inc(&neigh->probes);