__rtc_read_alarm missing month/year field bug?

[Joe Lawrence]

Hello Alessandro and Alexandre,

I noticed an interesting cmos_rtc.rtc.aie_timer on a Stratus machine
running the 4.6 kernel, with an expiration time that puts the alarm way
out into next year.  This is easily reproducible on this machine by
setting a wakealarm sometime in the near future, then rebooting.

>From a fresh boot:

  % cat /proc/driver/rtc
  rtc_time        : 17:55:10
  rtc_date        : 2016-06-09
  alrm_time       : 14:04:37
  alrm_date       : 2017-06-09         << 2017 ?
  alarm_IRQ       : no
  alrm_pending    : no
  update IRQ enabled      : no
  periodic IRQ enabled    : no
  periodic IRQ frequency  : 1024
  max user IRQ frequency  : 64
  24hr            : yes
  periodic_IRQ    : no
  update_IRQ      : no
  HPET_emulated   : yes
  BCD             : yes
  DST_enable      : no
  periodic_freq   : 1024
  batt_status     : okay


I added some debugging code to the kernel, saw this on the next boot:

  __rtc_read_alarm: A - alarm->time.tm_year = -1, missing = 0
  __rtc_read_alarm: B - alarm->time.tm_year = 116, missing = 3
  __rtc_read_alarm: C - alarm->time.tm_year = 117


Corresponding to these parts of __rtc_read_alarm:

  int __rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
  ...
  	enum { none, day, month, year } missing = none;
  ...
  		err = rtc_read_alarm_internal(rtc, alarm);
  ...
  	/* Fill in the missing alarm fields using the timestamp; we
  	 * know there's at least one since alarm->time is invalid.
  	 */
  ...
  [A]
  	if (alarm->time.tm_year == -1) {
  		alarm->time.tm_year = now.tm_year;
  		if (missing == none)
  			missing = year;
  	}
  [B]
  ...
  	switch (missing) {
  ...
  	/* Year rollover ... easy except for leap years! */
  	case year:
  		dev_dbg(&rtc->dev, "alarm rollover: %s\n", "year");
  		do {
  			alarm->time.tm_year++;
  		} while (!is_leap_year(alarm->time.tm_year + 1900)
  			&& rtc_valid_tm(&alarm->time) != 0);
  [C]		break;


I noticed that the missing year and month cases increment their
respective time units inside a do ... while (condition) loop, pushing
the default 'filled-in' values to now + 1.

Should this 'roll-over' code check for a valid date before incrementing
the alarm time?  (See attached patch.)  I think this might also apply to
a missing month field as well.

(After the patch + reboot):

  % cat /proc/driver/rtc
  rtc_time        : 18:24:02
  rtc_date        : 2016-06-09
  alrm_time       : 14:04:37
  alrm_date       : 2016-06-09
  alarm_IRQ       : no
  alrm_pending    : no
  update IRQ enabled      : no
  periodic IRQ enabled    : no
  periodic IRQ frequency  : 1024
  max user IRQ frequency  : 64
  24hr            : yes
  periodic_IRQ    : no
  update_IRQ      : no
  HPET_emulated   : yes
  BCD             : yes
  DST_enable      : no
  periodic_freq   : 1024
  batt_status     : okay

-- >8 --