Re: [PATCH v1] ptp: ocp: fix NULL deref in _signal_summary_show

[Sagi Maimon]

On Mon, Apr 14, 2025 at 4:01 PM Vadim Fedorenko
<vadim.fedorenko@xxxxxxxxx> wrote:
>
> On 14/04/2025 12:38, Sagi Maimon wrote:
> > On Mon, Apr 14, 2025 at 2:09 PM Vadim Fedorenko
> > <vadim.fedorenko@xxxxxxxxx> wrote:
> >>
> >> On 14/04/2025 11:56, Sagi Maimon wrote:
> >>> On Mon, Apr 14, 2025 at 12:37 PM Vadim Fedorenko
> >>> <vadim.fedorenko@xxxxxxxxx> 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@xxxxxxxxx>
> >>>>> ---
> >>>>>     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?
> >>> 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
> >>
>