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

[Sagi Maimon]

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?
> > 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
>