rtc: allow validated RTC_PIE_ON for non-root

drivers/char/rtc.c allowed RTC_PIE_ON ioctls for non-root users, as long as
the current interval (set via RTC_IRQP_SET) is <= max_user_freq.  Allow
RTC_PIE_ON under the same conditions when /dev/rtc* is handled by the rtc
subsystem.
Signed-off-by: NBryan Kadzban <bryan@kdzbn.homelinux.net>
Acked-by: NAlessandro Zummo <alessandro.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-dev.c

@@ -233,7 +233,8 @@ static int rtc_dev_ioctl(struct inode *inode, struct file *file,
 		break;
 
 	case RTC_PIE_ON:
-		if (!capable(CAP_SYS_RESOURCE))
+		if (rtc->irq_freq > rtc->max_user_freq &&
+				!capable(CAP_SYS_RESOURCE))
 			return -EACCES;
 		break;
 	}