Re: [PATCH] net: macb: fix NULL dereference due to no pcs_config method

[Nicolas Ferre]

On 05/11/2020 at 16:48, Russell King - ARM Linux admin wrote:
> On Thu, Nov 05, 2020 at 04:22:18PM +0100, Nicolas Ferre wrote:
> > On 05/11/2020 at 15:37, Parshuram Thombare wrote:
> > > This patch fixes NULL pointer dereference due to NULL pcs_config
> > > in pcs_ops.
> > >
> > > Fixes: e4e143e26ce8 ("net: macb: add support for high speed interface")
> >
> > What is this tag? In linux-next? As patch is not yet in Linus' tree, you
> > cannot refer to it like this.
> >
> > > Reported-by: Nicolas Ferre <Nicolas.Ferre@xxxxxxxxxxxxx>
> > > Link: https://lkml.org/lkml/2020/11/4/482
> >
> > You might need to change this to a "lore" link:
> > https://lore.kernel.org/netdev/2db854c7-9ffb-328a-f346-f68982723d29@xxxxxxxxxxxxx/
> >
> > > Signed-off-by: Parshuram Thombare <pthombar@xxxxxxxxxxx>
> >
> > This fix looks a bit weird to me. What about proposing a patch to Russell
> > like the chunk that you already identified in function
> > phylink_major_config()?
>
> No thanks. macb is currently the only case where a stub implementation
> for pcs_config() is required, which only occurs because the only
> appropriate protocol supported there is SGMII and not 1000base-X as
> well.

Got it.

> > > ---
> > >    drivers/net/ethernet/cadence/macb_main.c | 17 +++++++++++++++--
> > >    1 file changed, 15 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> > > index b7bc160..130a5af 100644
> > > --- a/drivers/net/ethernet/cadence/macb_main.c
> > > +++ b/drivers/net/ethernet/cadence/macb_main.c
> > > @@ -633,6 +633,15 @@ static void macb_pcs_an_restart(struct phylink_pcs *pcs)
> > >           /* Not supported */
> > >    }
> > >
> > > +static int macb_pcs_config(struct phylink_pcs *pcs,
> > > +                          unsigned int mode,
> > > +                          phy_interface_t interface,
> > > +                          const unsigned long *advertising,
> > > +                          bool permit_pause_to_mac)
> > > +{
> > > +       return 0;
> > > +}
> >
> > Russell, is the requirement for this void function intended?
>
> In response to v3 of the patch on 21st October, I said, and I quote:
>
>    I think all that needs to happen is a pcs_ops for the non-10GBASE-R
>    mode which moves macb_mac_pcs_get_state() and macb_mac_an_restart()
>    to it, and implements a stub pcs_config(). So it should be simple
>    to do.
>
> Obviously, my advice was not followed, I didn't spot the lack of it
> in v4 (sorry), and the result is the NULL pointer oops.

Fair enough. So Parshuram I'll add my ack tag when you re-send your 
patch with little issues fixed.

Thanks for your help Russell.

Best regards,
  Nicolas
--
Nicolas Ferre