Re: [PATCH net] net: ethtool: pse-pd: Fix possible null-deref

[Jakub Kicinski <kuba@kernel.org>]

On Tue, 9 Jul 2024 16:43:05 +0200 Kory Maincent wrote:
> > Normal ethtool flow is to first fill in the data with a ->get() then
> > modify what user wants to change.
> > 
> > Either we need:
> >  - an explanation in the commit message how this keeps old config; or
> >  - a ->get() to keep the previous values; or
> >  - just reject setting one value but not the other in
> >    ethnl_set_pse_validate() (assuming it never worked, anyway).  
> 
> In fact it is the contrary we can't set both value at the same time because a
> PSE port can't be a PoE and a PoDL power interface at the same time.

In that case maybe we should have an inverse condition in validate, too?
Something like:

	if ((pse_has_podl(phydev->psec) &&
	     GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_PODL_PSE_ADMIN_CONTROL)) ||
	    (pse_has_c33(phydev->psec) &&
	     GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_C33_PSE_ADMIN_CONTROL)))
		return -EINVAL;

GENL_REQ_ATTR_CHECK will set the extack for us.