[NETFILTER]: arp_tables: fix table locking in arpt_do_table

table->private might change because of ruleset changes, don't use it
without holding the lock.
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/netfilter/arp_tables.c

@@ -236,7 +236,7 @@ unsigned int arpt_do_table(struct sk_buff **pskb,
 	struct arpt_entry *e, *back;
 	const char *indev, *outdev;
 	void *table_base;
-	struct xt_table_info *private = table->private;
+	struct xt_table_info *private;
 
 	/* ARP header, plus 2 device addresses, plus 2 IP addresses.  */
 	if (!pskb_may_pull((*pskb), (sizeof(struct arphdr) +
@@ -248,6 +248,7 @@ unsigned int arpt_do_table(struct sk_buff **pskb,
 	outdev = out ? out->name : nulldevname;
 
 	read_lock_bh(&table->lock);
+	private = table->private;
 	table_base = (void *)private->entries[smp_processor_id()];
 	e = get_entry(table_base, private->hook_entry[hook]);
 	back = get_entry(table_base, private->underflow[hook]);