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

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Message-ID: <CAMuE1bFk=LFTWfu8RFJeSoPtjO8ieJDdEHhHpKYr4QxqB-7BBg@mail.gmail.com>
Date: Wed, 16 Apr 2025 09:33:59 +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 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?
> >>>>> 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
> >>>>
> >>
>