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

[Vadim Fedorenko]

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.

> > > 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