linux-kernel - [094/107] drivers/misc/lkdtm.c: fix race when crashpoint is hit multiple times before checking count

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Date:	Thu, 07 Jul 2011 17:17:06 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Josh Hunt <johunt@...mai.com>, Ankita Garg <ankita@...ibm.com>
Subject: [094/107] drivers/misc/lkdtm.c: fix race when crashpoint is hit multiple times before checking count

2.6.39-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Josh Hunt <johunt@...mai.com>

commit aa2c96d6f329e66cc59352b0f12e8f04e6a9593b upstream.

We observed the crash point count going negative in cases where the
crash point is hit multiple times before the check of "count == 0" is
done.  Because of this we never call lkdtm_do_action().  This patch just
adds a spinlock to protect count.

Reported-by: Tapan Dhimant <tdhimant@...mai.com>
Signed-off-by: Josh Hunt <johunt@...mai.com>
Acked-by: Ankita Garg <ankita@...ibm.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/misc/lkdtm.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/misc/lkdtm.c
+++ b/drivers/misc/lkdtm.c
@@ -120,6 +120,7 @@ static int recur_count = REC_NUM_DEFAULT
 static enum cname cpoint = CN_INVALID;
 static enum ctype cptype = CT_NONE;
 static int count = DEFAULT_COUNT;
+static DEFINE_SPINLOCK(count_lock);
 
 module_param(recur_count, int, 0644);
 MODULE_PARM_DESC(recur_count, " Recursion level for the stack overflow test, "\
@@ -230,11 +231,14 @@ static const char *cp_name_to_str(enum c
 static int lkdtm_parse_commandline(void)
 {
 	int i;
+	unsigned long flags;
 
 	if (cpoint_count < 1 || recur_count < 1)
 		return -EINVAL;
 
+	spin_lock_irqsave(&count_lock, flags);
 	count = cpoint_count;
+	spin_unlock_irqrestore(&count_lock, flags);
 
 	/* No special parameters */
 	if (!cpoint_type && !cpoint_name)
@@ -349,6 +353,9 @@ static void lkdtm_do_action(enum ctype w
 
 static void lkdtm_handler(void)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&count_lock, flags);
 	count--;
 	printk(KERN_INFO "lkdtm: Crash point %s of type %s hit, trigger in %d rounds\n",
 			cp_name_to_str(cpoint), cp_type_to_str(cptype), count);
@@ -357,6 +364,7 @@ static void lkdtm_handler(void)
 		lkdtm_do_action(cptype);
 		count = cpoint_count;
 	}
+	spin_unlock_irqrestore(&count_lock, flags);
 }
 
 static int lkdtm_register_cpoint(enum cname which)


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