rtc: cmos: zero-init wkalrm when reading from CMOS

cmos_read_alarm() may leave certain fields of a struct rtc_wkalrm
untouched; therefore, these fields contain garbage if not properly
initialized, leading to inconsistent values when converting into
time64_t. This patch to zero initialize the struct before calling
cmos_read_alarm().

Note that this patch is not intended to produce a correct time64_t, it
is only to produce a consistent value. In the case of suspend/resume, a
correct time64_t is not necessary; a consistent value is sufficient to
correctly perform an equality test for t_current_expires and
t_saved_expires. Logic to deduce a correct time64_t is expensive and
hence should be avoided.

Signed-off-by: Victor Ding <victording@google.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200814191654.v2.1.Iaf7638a2f2a87ff68d85fcb8dec615e41340c97f@changeid

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index bcc96ab7793fd3e30c9945f1fddcc5242c367891..c633319cdb91319d8af218ec4eda30503e59ec4e 100644 (file)
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -1006,6 +1006,7 @@ static int cmos_suspend(struct device *dev)
                        enable_irq_wake(cmos->irq);
        }
 
+       memset(&cmos->saved_wkalrm, 0, sizeof(struct rtc_wkalrm));
        cmos_read_alarm(dev, &cmos->saved_wkalrm);
 
        dev_dbg(dev, "suspend%s, ctrl %02x\n",
@@ -1054,6 +1055,7 @@ static void cmos_check_wkalrm(struct device *dev)
                return;
        }
 
+       memset(&current_alarm, 0, sizeof(struct rtc_wkalrm));
        cmos_read_alarm(dev, &current_alarm);
        t_current_expires = rtc_tm_to_time64(&current_alarm.time);
        t_saved_expires = rtc_tm_to_time64(&cmos->saved_wkalrm.time);