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Date:	Thu, 3 Jan 2013 14:20:29 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Paris <eparis@...hat.com>
Subject: Re: schedule_timeout: wrong timeout value fffffffffffffff0

On Wed, 2 Jan 2013 10:27:27 -0500
Dave Jones <davej@...hat.com> wrote:

> This happened to a box I left running fuzz tests over the holidays.
> 
> 
> schedule_timeout: wrong timeout value fffffffffffffff0
> Pid: 6606, comm: trinity-child1 Not tainted 3.8.0-rc1+ #43
> Call Trace:
>  [<ffffffff81698415>] schedule_timeout+0x305/0x340
>  [<ffffffff8169ae82>] ? preempt_schedule+0x42/0x60
>  [<ffffffff8169cb65>] ? _raw_spin_unlock_irqrestore+0x75/0x80
>  [<ffffffff810dc461>] audit_log_start+0x311/0x470
>  [<ffffffff8106c62c>] ? __rcu_read_unlock+0x5c/0xa0
>  [<ffffffff81086120>] ? try_to_wake_up+0x320/0x320
>  [<ffffffff810e0d0b>] audit_log_exit+0x4b/0xfb0
>  [<ffffffff81156e1b>] ? vm_mmap_pgoff+0x8b/0xb0
>  [<ffffffff810b2342>] ? get_lock_stats+0x22/0x70
>  [<ffffffff810b27ae>] ? put_lock_stats.isra.23+0xe/0x40
>  [<ffffffff810b2ecb>] ? lock_release_holdtime.part.24+0xcb/0x130
>  [<ffffffff81075f93>] ? up_write+0x23/0x40
>  [<ffffffff81156e1b>] ? vm_mmap_pgoff+0x8b/0xb0
>  [<ffffffff816a4afc>] ? sysret_signal+0x5/0x47
>  [<ffffffff810e3d3f>] __audit_syscall_exit+0x25f/0x2c0
>  [<ffffffff816a4bad>] sysret_audit+0x17/0x21
> 

ooh, I can fix that.  Please review.

From: Andrew Morton <akpm@...ux-foundation.org>
Subject: kernel/audit.c: avoid negative sleep durations

audit_log_start() performs the same jiffies comparison in two places.  If
sufficient time has elapsed between the two comparisons, the second one
produces a negative sleep duration:

schedule_timeout: wrong timeout value fffffffffffffff0
Pid: 6606, comm: trinity-child1 Not tainted 3.8.0-rc1+ #43
Call Trace:
 [<ffffffff81698415>] schedule_timeout+0x305/0x340
 [<ffffffff8169ae82>] ? preempt_schedule+0x42/0x60
 [<ffffffff8169cb65>] ? _raw_spin_unlock_irqrestore+0x75/0x80
 [<ffffffff810dc461>] audit_log_start+0x311/0x470
 [<ffffffff8106c62c>] ? __rcu_read_unlock+0x5c/0xa0
 [<ffffffff81086120>] ? try_to_wake_up+0x320/0x320
 [<ffffffff810e0d0b>] audit_log_exit+0x4b/0xfb0
 [<ffffffff81156e1b>] ? vm_mmap_pgoff+0x8b/0xb0
 [<ffffffff810b2342>] ? get_lock_stats+0x22/0x70
 [<ffffffff810b27ae>] ? put_lock_stats.isra.23+0xe/0x40
 [<ffffffff810b2ecb>] ? lock_release_holdtime.part.24+0xcb/0x130
 [<ffffffff81075f93>] ? up_write+0x23/0x40
 [<ffffffff81156e1b>] ? vm_mmap_pgoff+0x8b/0xb0
 [<ffffffff816a4afc>] ? sysret_signal+0x5/0x47
 [<ffffffff810e3d3f>] __audit_syscall_exit+0x25f/0x2c0
 [<ffffffff816a4bad>] sysret_audit+0x17/0x21

Fix it by performing the comparison a single time.

Reported-by: Dave Jones <davej@...hat.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Eric Paris <eparis@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 kernel/audit.c |   36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff -puN kernel/audit.c~a kernel/audit.c
--- a/kernel/audit.c~a
+++ a/kernel/audit.c
@@ -1101,6 +1101,23 @@ static inline void audit_get_stamp(struc
 	}
 }
 
+/*
+ * Wait for auditd to drain the queue a little
+ */
+static void wait_for_auditd(unsigned long sleep_time)
+{
+	DECLARE_WAITQUEUE(wait, current);
+	set_current_state(TASK_INTERRUPTIBLE);
+	add_wait_queue(&audit_backlog_wait, &wait);
+
+	if (audit_backlog_limit &&
+	    skb_queue_len(&audit_skb_queue) > audit_backlog_limit)
+		schedule_timeout(sleep_time);
+
+	__set_current_state(TASK_RUNNING);
+	remove_wait_queue(&audit_backlog_wait, &wait);
+}
+
 /* Obtain an audit buffer.  This routine does locking to obtain the
  * audit buffer, but then no locking is required for calls to
  * audit_log_*format.  If the tsk is a task that is currently in a
@@ -1146,20 +1163,13 @@ struct audit_buffer *audit_log_start(str
 
 	while (audit_backlog_limit
 	       && skb_queue_len(&audit_skb_queue) > audit_backlog_limit + reserve) {
-		if (gfp_mask & __GFP_WAIT && audit_backlog_wait_time
-		    && time_before(jiffies, timeout_start + audit_backlog_wait_time)) {
-
-			/* Wait for auditd to drain the queue a little */
-			DECLARE_WAITQUEUE(wait, current);
-			set_current_state(TASK_INTERRUPTIBLE);
-			add_wait_queue(&audit_backlog_wait, &wait);
-
-			if (audit_backlog_limit &&
-			    skb_queue_len(&audit_skb_queue) > audit_backlog_limit)
-				schedule_timeout(timeout_start + audit_backlog_wait_time - jiffies);
+		if (gfp_mask & __GFP_WAIT && audit_backlog_wait_time) {
+			unsigned long sleep_time;
 
-			__set_current_state(TASK_RUNNING);
-			remove_wait_queue(&audit_backlog_wait, &wait);
+			sleep_time = timeout_start + audit_backlog_wait_time -
+					jiffies;
+			if ((long)sleep_time > 0)
+				wait_for_auditd(sleep_time);
 			continue;
 		}
 		if (audit_rate_check() && printk_ratelimit())
_

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