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 <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Chris Wright <[email protected]>
--- 1/net/ipv4/netfilter/ip_queue.c 2005-05-27 09:44:32.000000000 +0200
+++ 2/net/ipv4/netfilter/ip_queue.c 2005-05-27 09:47:13.000000000 +0200
@@ -3,6 +3,7 @@
* communicating with userspace via netlink.
*
* (C) 2000-2002 James Morris <[email protected]>
+ * (C) 2003-2005 Netfilter Core Team <[email protected]>
*
* 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
@@ -14,6 +15,7 @@
* Zander).
* 2000-08-01: Added Nick Williams' MAC support.
* 2002-06-25: Code cleanup.
+ * 2005-05-26: local_bh_{disable,enable} around nf_reinject (Harald Welte)
*
*/
#include <linux/module.h>
@@ -66,7 +68,15 @@
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);
}
-
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