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

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Date: Tue, 1 Aug 2023 11:11:17 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Lin Ma <linma@....edu.cn>, davem@...emloft.net, edumazet@...gle.com,
	pabeni@...hat.com, fw@...len.de, yang.lee@...ux.alibaba.com,
	jgg@...pe.ca, markzhang@...dia.com, phaddad@...dia.com,
	yuancan@...wei.com, ohartoov@...dia.com, chenzhongjin@...wei.com,
	aharonl@...dia.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net v1 1/2] netlink: let len field used to parse
 type-not-care nested attrs

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