linux-kernel - Re: [PATCH] rtc: fix use of uninit struct in rtc_read_alarm

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Message-ID: <2025040814444859857143@mail.local>
Date: Tue, 8 Apr 2025 16:44:48 +0200
From: Alexandre Belloni <alexandre.belloni@...tlin.com>
To: Bharadwaj Raju <bharadwaj.raju777@...il.com>
Cc: linux-rtc@...r.kernel.org, shuah@...nel.org,
	linux-kernel@...r.kernel.org, linux-kernel-mentees@...ts.linux.dev
Subject: Re: [PATCH] rtc: fix use of uninit struct in rtc_read_alarm_internal

Hello,

On 29/03/2025 19:59:46+0530, Bharadwaj Raju wrote:
> On Tue, Mar 18, 2025 at 3:21 AM Alexandre Belloni
> <alexandre.belloni@...tlin.com> 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@...il.com>
> > > ---
> > >  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?

I've sent my patch now.

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com