RTC: Prevents a division by zero in kernel code.

This patch prevents a user space program from calling the RTC_IRQP_SET
ioctl with a negative value of frequency. Also, if this call is make
with a zero value of frequency, there would be a division by zero in the
kernel code.

[jstultz: Also initialize irq_freq to 1 to catch other divbyzero issues]

CC: Alessandro Zummo <a.zummo@towertech.it>
CC: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Marcelo Roberto Jimenez <mroberto@cpti.cetuc.puc-rio.br>
Signed-off-by: John Stultz <john.stultz@linaro.org>

2 files changed, 4 insertions, 0 deletions

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 9583cbcc6b79..c404b61386bf 100644
--- a/drivers/rtc/class.c
+++ b/drivers/rtc/class.c
@@ -143,6 +143,7 @@ struct rtc_device *rtc_device_register(const char *name, struct device *dev,
         rtc->id = id;
         rtc->ops = ops;
         rtc->owner = owner;
+        rtc->irq_freq = 1;
         rtc->max_user_freq = 64;
         rtc->dev.parent = dev;
         rtc->dev.class = rtc_class;
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
index 925006d33109..a0c01967244d 100644
--- a/drivers/rtc/interface.c
+++ b/drivers/rtc/interface.c
@@ -464,6 +464,9 @@ int rtc_irq_set_freq(struct rtc_device *rtc, struct rtc_task *task, int freq)
         int err = 0;
         unsigned long flags;
 
+        if (freq <= 0)
+                return -EINVAL;
+
         spin_lock_irqsave(&rtc->irq_task_lock, flags);
         if (rtc->irq_task != NULL && task == NULL)
                 err = -EBUSY;