netdev - Re: [PATCH RESEND net] ptp: Ensure info->enable callback is always set

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Message-ID: <779708b6-d61c-4688-92cc-6afb987334d6@t-8ch.de>
Date: Thu, 23 Jan 2025 14:19:46 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
Cc: Richard Cochran <richardcochran@...il.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, John Stultz <john.stultz@...aro.org>, 
	Arnd Bergmann <arnd@...db.de>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH RESEND net] ptp: Ensure info->enable callback is always
 set

On 2025-01-23 10:38:37+0100, Michal Swiatkowski wrote:
> On Thu, Jan 23, 2025 at 08:22:40AM +0100, Thomas Weißschuh wrote:
> > The ioctl and sysfs handlers unconditionally call the ->enable callback.
> > Not all drivers implement that callback, leading to NULL dereferences.
> > Example of affected drivers: ptp_s390.c, ptp_vclock.c and ptp_mock.c.
> > 
> > Instead use a dummy callback if no better was specified by the driver.
> > 
> > Fixes: d94ba80ebbea ("ptp: Added a brand new class driver for ptp clocks.")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> > ---
> >  drivers/ptp/ptp_clock.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
> > index b932425ddc6a3789504164a69d1b8eba47da462c..35a5994bf64f6373c08269d63aaeac3f4ab31ff0 100644
> > --- a/drivers/ptp/ptp_clock.c
> > +++ b/drivers/ptp/ptp_clock.c
> > @@ -217,6 +217,11 @@ static int ptp_getcycles64(struct ptp_clock_info *info, struct timespec64 *ts)
> >  		return info->gettime64(info, ts);
> >  }
> >  
> > +static int ptp_enable(struct ptp_clock_info *ptp, struct ptp_clock_request *request, int on)
> > +{
> > +	return -EOPNOTSUPP;
> > +}
> > +
> >  static void ptp_aux_kworker(struct kthread_work *work)
> >  {
> >  	struct ptp_clock *ptp = container_of(work, struct ptp_clock,
> > @@ -294,6 +299,9 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
> >  			ptp->info->getcrosscycles = ptp->info->getcrosststamp;
> >  	}
> >  
> > +	if (!ptp->info->enable)
> > +		ptp->info->enable = ptp_enable;
> > +
> >  	if (ptp->info->do_aux_work) {
> >  		kthread_init_delayed_work(&ptp->aux_work, ptp_aux_kworker);
> >  		ptp->kworker = kthread_run_worker(0, "ptp%d", ptp->index);
> > 
> > ---
> > base-commit: c4b9570cfb63501638db720f3bee9f6dfd044b82
> > change-id: 20250122-ptp-enable-831339c62428
> > 
> > Best regards,
> > -- 
> > Thomas Weißschuh <linux@...ssschuh.net>
> 
> Reviewed-by: Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>
> 
> What about other ops, did you check it too? Looks like it isn't needed,
> but it sometimes hard to follow.

I couldn't find any missing, but I'm not familiar with the subsystem and
didn't check too hard.

Note:

A follow-up fix would be to actually guard the users of ->enable and
error out. For sysfs the attributes could be hidden completely.
That would be a nicer user interface but more code change which are not
so easily backportable.


Thomas