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Date: Tue, 25 Jul 2023 08:54:34 +0300
From: Leon Romanovsky <leon@kernel.org>
To: Lin Ma <linma@zju.edu.cn>
Cc: kuba@kernel.org, davem@davemloft.net, edumazet@google.com,
	pabeni@redhat.com, ast@kernel.org, martin.lau@kernel.org,
	yhs@fb.com, void@manifault.com, andrii@kernel.org,
	houtao1@huawei.com, inwardvessel@gmail.com, kuniyu@amazon.com,
	songliubraving@fb.com, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH v2] bpf: Add length check for
 SK_DIAG_BPF_STORAGE_REQ_MAP_FD parsing
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 <20230725044409.GF11388@unreal>
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In-Reply-To: <15dc24fc.e7c38.1898b81ac08.Coremail.linma@zju.edu.cn>

On Tue, Jul 25, 2023 at 01:24:38PM +0800, Lin Ma wrote:
> 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.

My concern is related to maintainability in long run. Your check adds
another layer of cabal knowledge which will be copied/pasted in other
places.

Thanks

> 
> Regards
> Lin