drivers/rtc/interface.c: fix alarm rollover when day or month is out-of-range

Commit f44f7f96 ("RTC: Initialize kernel state from RTC") introduced a
potential infinite loop.  If an alarm time contains a wildcard month and
an invalid day (> 31), or a wildcard year and an invalid month (>= 12),
the loop searching for the next matching date will never terminate.  Treat
the invalid values as wildcards.

Fixes <http://bugs.debian.org/646429>, <http://bugs.debian.org/653331>
Reported-by: leo weppelman <leoweppelman@googlemail.com>
Reported-by: "P. van Gaans" <mailme667@yahoo.co.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Marcelo Roberto Jimenez <mroberto@cpti.cetuc.puc-rio.br>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/interface.c

@@ -228,11 +228,11 @@ int __rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
 		alarm->time.tm_hour = now.tm_hour;
 
 	/* For simplicity, only support date rollover for now */
-	if (alarm->time.tm_mday == -1) {
+	if (alarm->time.tm_mday < 1 || alarm->time.tm_mday > 31) {
 		alarm->time.tm_mday = now.tm_mday;
 		missing = day;
 	}
-	if (alarm->time.tm_mon == -1) {
+	if ((unsigned)alarm->time.tm_mon >= 12) {
 		alarm->time.tm_mon = now.tm_mon;
 		if (missing == none)
 			missing = month;