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

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Message-ID: <b4d675a4-b7ad-4ecf-8d19-6bf08b452472@linux.dev>
Date: Wed, 29 Oct 2025 18:55:59 +0000
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Tim Hostetler <thostet@...gle.com>
Cc: Kuniyuki Iwashima <kuniyu@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 richardcochran@...il.com, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, junjie.cao@...el.com, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, pabeni@...hat.com,
 syzbot+c8c0e7ccabd456541612@...kaller.appspotmail.com,
 syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] ptp: guard ptp_clock_gettime() if neither gettimex64 nor

On 29/10/2025 16:37, Tim Hostetler wrote:
> On Tue, Oct 28, 2025 at 4:57 PM Vadim Fedorenko
> <vadim.fedorenko@...ux.dev> wrote:
>>
>> On 28.10.2025 23:54, Kuniyuki Iwashima wrote:
>>> On Tue, Oct 28, 2025 at 4:45 PM Vadim Fedorenko
>>> <vadim.fedorenko@...ux.dev> 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@...il.com>
>>>>>> 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.