linux-kernel - [017/102] rtc: limit frequency

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Date:	Wed, 03 Aug 2011 15:00:37 -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,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ben Greear <greearb@...delatech.com>
Subject: [017/102] rtc: limit frequency

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

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

From: Thomas Gleixner <tglx@...utronix.de>

commit 431e2bcc371016824f419baa745f82388258f3ee upstream.

Due to the hrtimer self rearming mode a user can DoS the machine simply
because it's starved by hrtimer events.

The RTC hrtimer is self rearming.  We really need to limit the frequency
to something sensible.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Ben Greear <greearb@...delatech.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/rtc/interface.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -708,7 +708,7 @@ int rtc_irq_set_freq(struct rtc_device *
 	int err = 0;
 	unsigned long flags;
 
-	if (freq <= 0)
+	if (freq <= 0 || freq > 5000)
 		return -EINVAL;
 retry:
 	spin_lock_irqsave(&rtc->irq_task_lock, flags);


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