Re: [PATCH] ptp: guard ptp_clock_gettime() if neither gettimex64 nor

[Vadim Fedorenko]

On 29/10/2025 16:37, Tim Hostetler wrote:
> On Tue, Oct 28, 2025 at 4:57 PM Vadim Fedorenko
> <vadim.fedorenko@xxxxxxxxx> wrote:
> > On 28.10.2025 23:54, Kuniyuki Iwashima wrote:
> > > On Tue, Oct 28, 2025 at 4:45 PM Vadim Fedorenko
> > > <vadim.fedorenko@xxxxxxxxx> wrote:
> > > > On 28.10.2025 23:13, Jakub Kicinski wrote:
> > > > > On Tue, 28 Oct 2025 15:51:50 +0000 Kuniyuki Iwashima wrote:
> > > > > > From: Richard Cochran <richardcochran@xxxxxxxxx>
> > > > > > Date: Tue, 28 Oct 2025 07:09:41 -0700
> > > > > > > On Tue, Oct 28, 2025 at 05:51:43PM +0800, Junjie Cao wrote:
> > > > > > > > Syzbot reports a NULL function pointer call on arm64 when
> > > > > > > > ptp_clock_gettime() falls back to ->gettime64() and the driver provides
> > > > > > > > neither ->gettimex64() nor ->gettime64(). This leads to a crash in the
> > > > > > > > posix clock gettime path.
> > > > > > >
> > > > > > > Drivers must provide a gettime method.
> > > > > > >
> > > > > > > If they do not, then that is a bug in the driver.
> > > > > >
> > > > > > AFAICT, only GVE does not have gettime() and settime(), and
> > > > > > Tim (CCed) was preparing a fix and mostly ready to post it.
> > > > >
> > > > > cc: Vadim who promised me a PTP driver test :) Let's make sure we
> > > > > tickle gettime/setting in that test..
> > > >
> > > > Heh, call gettime/settime is easy. But in case of absence of these callbacks
> > > > the kernel will crash - not sure we can gather good signal in such case?
> > >
> > > At least we could catch it on NIPA.
> > >
> > > but I suggested Tim adding WARN_ON_ONCE(!info->gettime64 &&
> > > !info-> getimex64) in ptp_clock_register() so that a developer can
> > > notice that even while loading a buggy module.
> >
> > Yeah, that looks like a solution
>
> Yes, I was actually going to post the fix to gve today (I'll still do
> that as ptp_clock_gettime() is not the only function to assume a
> gettime64 or gettimex64 implementation) and shortly after posting
> Kuniyuki's suggested fix to ptp_clock_register() as such:
>
> diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
> index ef020599b771..f2d9cf4a455e 100644
> --- a/drivers/ptp/ptp_clock.c
> +++ b/drivers/ptp/ptp_clock.c
> @@ -325,6 +325,9 @@ struct ptp_clock *ptp_clock_register(struct
> ptp_clock_info *info,
>          if (info->n_alarm > PTP_MAX_ALARMS)
>                  return ERR_PTR(-EINVAL);
>
> +       if (WARN_ON_ONCE(!info->gettimex64 && !info->gettime64))
> +               return ERR_PTR(-EINVAL);
> +
>          /* Initialize a clock structure. */
>          ptp = kzalloc(sizeof(struct ptp_clock), GFP_KERNEL);
>          if (!ptp) {
> --
>
> I also have a similar patch for checking for settime64's function pointer.
>
> But I have no objections to Junjie posting a v2 in this manner instead
> of waiting for me.

WARN_ON_ONCE is better in terms of reducing the amount of review work.
Driver developers will be automatically notified about improper
implementation while Junjie's patch will simply hide the problem.