[NETFILTER]: Fix deadlock with ip_queue and tcp local input path.

When we have ip_queue being used from LOCAL_IN, then we end up with a
situation where the verdicts coming back from userspace traverse the TCP
input path from syscall context. While this seems to work most of the
time, there's an ugly deadlock:

syscall context is interrupted by the timer interrupt. When the timer
interrupt leaves, the timer softirq get's scheduled and calls
tcp_delack_timer() and alike. They themselves do bh_lock_sock(sk),
which is already held from somewhere else -> boom.

I've now tested the suggested solution by Patrick McHardy and Herbert Xu to
simply use local_bh_{en,dis}able().

Signed-off-by: Harald Welte <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/netfilter/ip_queue.c

···
  * communicating with userspace via netlink.
  *
  * (C) 2000-2002 James Morris <[e-mail]>
+ * (C) 2003-2005 Netfilter Core Team <[e-mail]>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
···
  * 2005-01-10: Added /proc counter for dropped packets; fixed so
  *             packets aren't delivered to user space if they're going 
  *             to be dropped. 
+ * 2005-05-26: local_bh_{disable,enable} around nf_reinject (Harald Welte)
  *
  */
 #include <linux/module.h>
···
 static void
 ipq_issue_verdict(struct ipq_queue_entry *entry, int verdict)
 {
+	/* TCP input path (and probably other bits) assume to be called
+	 * from softirq context, not from syscall, like ipq_issue_verdict is
+	 * called.  TCP input path deadlocks with locks taken from timer
+	 * softirq, e.g.  We therefore emulate this by local_bh_disable() */
+
+	local_bh_disable();
 	nf_reinject(entry->skb, entry->info, verdict);
+	local_bh_enable();
+
 	kfree(entry);
 }