netdev - Re: [PATCH net-next 6/6] ethtool: specify which header flags are supported per command

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Message-ID: <d5824faed8a748dc2f73dab16f914377cf972bc4.camel@sipsolutions.net>
Date:   Mon, 05 Oct 2020 21:28:16 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kernel-team@...com,
        jiri@...nulli.us, andrew@...n.ch, mkubecek@...e.cz
Subject: Re: [PATCH net-next 6/6] ethtool: specify which header flags are
 supported per command

On Mon, 2020-10-05 at 12:25 -0700, Jakub Kicinski wrote:
> On Mon, 05 Oct 2020 20:58:57 +0200 Johannes Berg wrote:
> > On Mon, 2020-10-05 at 08:57 -0700, Jakub Kicinski wrote:
> > > @@ -47,19 +61,16 @@ int ethnl_parse_header_dev_get(struct ethnl_req_info *req_info,
> > >  		NL_SET_ERR_MSG(extack, "request header missing");
> > >  		return -EINVAL;
> > >  	}
> > > +	/* Use most permissive header policy here, ops should specify their
> > > +	 * actual header policy via NLA_POLICY_NESTED(), and the real
> > > +	 * validation will happen in genetlink code.
> > > +	 */
> > >  	ret = nla_parse_nested(tb, ETHTOOL_A_HEADER_MAX, header,
> > > -			       ethnl_header_policy, extack);
> > > +			       ethnl_header_policy_stats, extack);  
> > 
> > Would it make sense to just remove the validation here? It's already
> > done, so it just costs extra cycles and can't really fail, and if there
> > are more diverse policies in the future this might also very quickly get
> > out of hand?
> 
> I was slightly worried I missed a command and need last line of defence,

Ah. I was just about to suggest to put it into the family policy/maxattr
but that won't work of course since this is nested.

But actually what you _could_ put there is a dummy policy (non-NULL
pointer) with a maxattr of 0, and then all attrs will be completely
rejected for a command where the policy was missed.

Not if you missed the NLA_POLICY_NESTED() link, though.

johannes