Subject: Re: [PATCH net v1 1/2] netlink: let len field used to parse type-not-care nested attrs

From: Leon Romanovsky <[email-masked]>
Date: Tue, 1 Aug 2023 11:11:17 +0300

On Mon, Jul 31, 2023 at 12:03:26PM -0700, Jakub Kicinski wrote:
> On Mon, 31 Jul 2023 20:12:47 +0800 Lin Ma wrote:
> > In short, the very direct idea to fix such lengh-check-forgotten bug is
> > add nla_len() checks like
> > 
> >   if (nla_len(nla) < SOME_LEN)
> >     return -EINVAL;
> > 
> > However, this is tedious and just like Leon said: add another layer of
> > cabal knowledge. The better solution should leverage the nla_policy and
> > discard nlattr whose length is invalid when doing parsing. That is, we
> > should defined a nested_policy for the X above like
> 
> Hard no. Putting array index into attr type is an advanced case and the
> parsing code has to be able to deal with low level netlink details.

Jakub,

IMHO, you are lowering too much the separation line between simple vs.
advanced use cases. 

I had no idea that my use-case of passing nested netlink array is counted
as advanced usage.

Thanks