netdev - Re: [PATCH v2] bpf: Add length check for SK_DIAG_BPF_STORAGE_REQ_MAP

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Date: Tue, 25 Jul 2023 13:24:38 +0800 (GMT+08:00)
From: "Lin Ma" <linma@....edu.cn>
To: "Leon Romanovsky" <leon@...nel.org>
Cc: kuba@...nel.org, davem@...emloft.net, edumazet@...gle.com, 
	pabeni@...hat.com, ast@...nel.org, martin.lau@...nel.org, yhs@...com, 
	void@...ifault.com, andrii@...nel.org, houtao1@...wei.com, 
	inwardvessel@...il.com, kuniyu@...zon.com, songliubraving@...com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	bpf@...r.kernel.org
Subject: Re: [PATCH v2] bpf: Add length check for
 SK_DIAG_BPF_STORAGE_REQ_MAP_FD parsing

Hello Leon,

> 
> Jakub, it seems like Lin adds this check to all nla_for_each_nested() loops.
> IMHO, the better change will be to change nla_for_each_nested() skip empty/not valid NLAs.
> 
> Thanks

I guess you just get these fixes misunderstood. I do not add the nla_len check
to  **all nla_for_each_nested** :(. I only add checks to those who do not access 
the attributes without verifying the length, which is buggy.

The others, either do a similar nla_len check already or just do nla_validate
somewhere else. That is to say, they **validate** the relevant attributes.

In short, nla_for_each_nested is just a loop macro that iterates the nlattrs,
like nla_for_each macro. It is weird for them to do nlattr validation as there
could have already been a call to nla_validate to ensure those attributes are
correct. That is, for those who do not, a simple nla_len check is the simplest
and most efficient choice.

Regards
Lin