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    Subject[PATCH AUTOSEL for 3.18 059/102] rtc: interface: Validate alarm-time before handling rollover
    Date
    From: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>

    [ Upstream commit da96aea0ed177105cb13ee83b328f6c61e061d3f ]

    In function __rtc_read_alarm() its possible for an alarm time-stamp to
    be invalid even after replacing missing components with current
    time-stamp. The condition 'alarm->time.tm_year < 70' will trigger this
    case and will cause the call to 'rtc_tm_to_time64(&alarm->time)'
    return a negative value for variable t_alm.

    While handling alarm rollover this negative t_alm (assumed to seconds
    offset from '1970-01-01 00:00:00') is converted back to rtc_time via
    rtc_time64_to_tm() which results in this error log with seemingly
    garbage values:

    "rtc rtc0: invalid alarm value: -2-1--1041528741
    2005511117:71582844:32"

    This error was generated when the rtc driver (rtc-opal in this case)
    returned an alarm time-stamp of '00-00-00 00:00:00' to indicate that
    the alarm is disabled. Though I have submitted a separate fix for the
    rtc-opal driver, this issue may potentially impact other
    existing/future rtc drivers.

    To fix this issue the patch validates the alarm time-stamp just after
    filling up the missing datetime components and if rtc_valid_tm() still
    reports it to be invalid then bails out of the function without
    handling the rollover.

    Reported-by: Steve Best <sbest@redhat.com>
    Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
    Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    drivers/rtc/interface.c | 9 ++++++++-
    1 file changed, 8 insertions(+), 1 deletion(-)

    diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
    index 5b2717f5dafa..d4153892c120 100644
    --- a/drivers/rtc/interface.c
    +++ b/drivers/rtc/interface.c
    @@ -249,6 +249,13 @@ int __rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
    missing = year;
    }

    + /* Can't proceed if alarm is still invalid after replacing
    + * missing fields.
    + */
    + err = rtc_valid_tm(&alarm->time);
    + if (err)
    + goto done;
    +
    /* with luck, no rollover is needed */
    rtc_tm_to_time(&now, &t_now);
    rtc_tm_to_time(&alarm->time, &t_alm);
    @@ -300,9 +307,9 @@ int __rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
    dev_warn(&rtc->dev, "alarm rollover not handled\n");
    }

    -done:
    err = rtc_valid_tm(&alarm->time);

    +done:
    if (err) {
    dev_warn(&rtc->dev, "invalid alarm value: %d-%d-%d %d:%d:%d\n",
    alarm->time.tm_year + 1900, alarm->time.tm_mon + 1,
    --
    2.14.1
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