netdev - Re: [PATCH v1] ptp: ocp: fix NULL deref in _signal_summary

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Message-ID: <CAMuE1bFLB24ELFOSG=v+0hxJ+a+KGNWc8=Z3=kbXOs03PtLFOA@mail.gmail.com>
Date: Wed, 16 Apr 2025 16:59:33 +0300
From: Sagi Maimon <maimon.sagi@...il.com>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: jonathan.lemon@...il.com, richardcochran@...il.com, andrew+netdev@...n.ch, 
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v1] ptp: ocp: fix NULL deref in _signal_summary_show

On Wed, Apr 16, 2025 at 1:35 PM Vadim Fedorenko
<vadim.fedorenko@...ux.dev> wrote:
>
> On 16/04/2025 07:33, Sagi Maimon wrote:
> > On Mon, Apr 14, 2025 at 4:55 PM Vadim Fedorenko
> > <vadim.fedorenko@...ux.dev> wrote:
> >>
> >> On 14/04/2025 14:43, Sagi Maimon wrote:
> >>> On Mon, Apr 14, 2025 at 4:01 PM Vadim Fedorenko
> >>> <vadim.fedorenko@...ux.dev> wrote:
> >>>>
> >>>> On 14/04/2025 12:38, Sagi Maimon wrote:
> >>>>> On Mon, Apr 14, 2025 at 2:09 PM Vadim Fedorenko
> >>>>> <vadim.fedorenko@...ux.dev> wrote:
> >>>>>>
> >>>>>> On 14/04/2025 11:56, Sagi Maimon wrote:
> >>>>>>> On Mon, Apr 14, 2025 at 12:37 PM Vadim Fedorenko
> >>>>>>> <vadim.fedorenko@...ux.dev> wrote:
> >>>>>>>>
> >>>>>>>> On 14/04/2025 09:54, Sagi Maimon wrote:
> >>>>>>>>> Sysfs signal show operations can invoke _signal_summary_show before
> >>>>>>>>> signal_out array elements are initialized, causing a NULL pointer
> >>>>>>>>> dereference. Add NULL checks for signal_out elements to prevent kernel
> >>>>>>>>> crashes.
> >>>>>>>>>
> >>>>>>>>> Fixes: b325af3cfab9 ("ptp: ocp: Add signal generators and update sysfs nodes")
> >>>>>>>>> Signed-off-by: Sagi Maimon <maimon.sagi@...il.com>
> >>>>>>>>> ---
> >>>>>>>>>       drivers/ptp/ptp_ocp.c | 3 +++
> >>>>>>>>>       1 file changed, 3 insertions(+)
> >>>>>>>>>
> >>>>>>>>> diff --git a/drivers/ptp/ptp_ocp.c b/drivers/ptp/ptp_ocp.c
> >>>>>>>>> index 7945c6be1f7c..4c7893539cec 100644
> >>>>>>>>> --- a/drivers/ptp/ptp_ocp.c
> >>>>>>>>> +++ b/drivers/ptp/ptp_ocp.c
> >>>>>>>>> @@ -3963,6 +3963,9 @@ _signal_summary_show(struct seq_file *s, struct ptp_ocp *bp, int nr)
> >>>>>>>>>           bool on;
> >>>>>>>>>           u32 val;
> >>>>>>>>>
> >>>>>>>>> +     if (!bp->signal_out[nr])
> >>>>>>>>> +             return;
> >>>>>>>>> +
> >>>>>>>>>           on = signal->running;
> >>>>>>>>>           sprintf(label, "GEN%d", nr + 1);
> >>>>>>>>>           seq_printf(s, "%7s: %s, period:%llu duty:%d%% phase:%llu pol:%d",
> >>>>>>>>
> >>>>>>>> That's not correct, the dereference of bp->signal_out[nr] happens before
> >>>>>>>> the check. But I just wonder how can that even happen?
> >>>>>>>>
> >>>>>>> The scenario (our case): on ptp_ocp_adva_board_init we
> >>>>>>> initiate only signals 0 and 1 so 2 and 3 are NULL.
> >>>>>>> Later ptp_ocp_summary_show runs on all 4 signals and calls _signal_summary_show
> >>>>>>> when calling signal 2 or 3  the dereference occurs.
> >>>>>>> can you please explain: " the dereference of bp->signal_out[nr] happens before
> >>>>>>> the check", where exactly? do you mean in those lines:
> >>>>>>> struct signal_reg __iomem *reg = bp->signal_out[nr]->mem;
> >>>>>>        ^^^
> >>>>>> yes, this is the line which dereferences the pointer.
> >>>>>>
> >>>>>> but in case you have only 2 pins to configure, why the driver exposes 4
> >>>>>> SMAs? You can simply adjust the attributes (adva_timecard_attrs).
> >>>>>>
> >>>>> I can (and will) expose only 2 sma in adva_timecard_attrs, but still
> >>>>> ptp_ocp_summary_show runs
> >>>>> on all 4 signals and not only on the on that exposed, is it not a bug?
> >>>>
> >>>> Yeah, it's a bug, but different one, and we have to fix it other way.
> >>>>
> >>> Do you want to instruct me how to fix it , or will you fix it?
> >>
> >> well, the original device structure was not designed to have the amount
> >> of SMAs less than 4. We have to introduce another field to store actual
> >> amount of SMAs to work with, and adjust the code to check the value. The
> >> best solution would be to keep maximum amount of 4 SMAs in the structure
> >> but create a helper which will init new field and will have
> >> BUILD_BUG_ON() to prevent having more SMAs than fixed size array for
> >> them. That will solve your problem, but I will need to check it on the
> >> HW we run.
> >>
> > just to be clear you will write the fix and test it on your HW, so you
> > don't want me to write the fix?
>
> Well, it would be great if you can write the code which will make SMA
> functions flexible to the amount of pin the HW has. All our HW has fixed
> amount of 4 pins that's why the driver was coded with constants. Now
> your hardware has slightly different amount of pins, so it needs
> adjustments to the driver to work properly. I just want to be sure that
> any adjustments will not break my HW - that's what I meant saying I'll
> test it.
>
Just to be clear (correct me please if I am wrong):
I will write the code, then create a patch and upstream to the vanilla
you will test my change on your HW and only then approve the patch
> >>>>>>> struct ptp_ocp_signal *signal = &bp->signal[nr];
> >>>>>>>> I believe the proper fix is to move ptp_ocp_attr_group_add() closer to
> >>>>>>>> the end of ptp_ocp_adva_board_init() like it's done for other boards.
> >>>>>>>>
> >>>>>>>> --
> >>>>>>>> pw-bot: cr
> >>>>>>
> >>>>
> >>
>