Re: [PATCH] rtc: fix use of uninit struct in rtc_read_alarm_internal

[Bharadwaj Raju]

On Tue, Mar 18, 2025 at 3:21 AM Alexandre Belloni
<alexandre.belloni@xxxxxxxxxxx> wrote:
>
> On 18/03/2025 00:03:43+0530, Bharadwaj Raju wrote:
> > The trace call invokes rtc_tm_to_time64 on a
> > potentially uninitialized alarm->time. Move the
> > trace call to the path where we do successfully
> > initialize and read that struct.
> >
> > This fixes a KMSAN warning.
> >
> > Fixes: 29a1f599c0cc ("rtc: Add tracepoints for RTC system")
> >
> > Signed-off-by: Bharadwaj Raju <bharadwaj.raju777@xxxxxxxxx>
> > ---
> >  drivers/rtc/interface.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c
> > index aaf76406cd7d..82ba33bf478b 100644
> > --- a/drivers/rtc/interface.c
> > +++ b/drivers/rtc/interface.c
> > @@ -201,11 +201,12 @@ static int rtc_read_alarm_internal(struct rtc_device *rtc,
> >               alarm->time.tm_yday = -1;
> >               alarm->time.tm_isdst = -1;
> >               err = rtc->ops->read_alarm(rtc->dev.parent, alarm);
> > +             if (!err)
> > +                     trace_rtc_read_alarm(rtc_tm_to_time64(&alarm->time), err);
> >       }
> >
> >       mutex_unlock(&rtc->ops_lock);
> >
> > -     trace_rtc_read_alarm(rtc_tm_to_time64(&alarm->time), err);
>
> This removes the tracepoint when there is an error, rendering it les
> useful.
>
> Also, as discussed about a year ago, alarm-time being uninitialized is
> not actually an issue as mktime64 can handle whatever is the input so
> this will never cause any problem so this isn't really a fix.
>
> I suggest the following:

Thanks for reviewing. Would you like me to make a second version of
the patch with this suggestion?