netdev - Re: [PATCH] net: check the length of the data before dereferencing it

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Message-ID: <CABa6K_HfWckb=sv7oQatv2ZJm3EKJE0mutQQ-OiddXiR6E7eHg@mail.gmail.com>
Date:	Mon, 2 Apr 2012 11:45:05 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, kaber@...sh.net, pablo@...filter.org,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] net: check the length of the data before dereferencing it

On Mon, Apr 2, 2012 at 11:29 AM, David Miller <davem@...emloft.net> wrote:
>
> Tag Eric, you're it.
>
> You ACK'd this patch, so you get to show how this is actually able
> to cause some kind of problem.
>
> I assert that this is adding a useless test, that doesn't fix any kind
> of possible crash or misbehavior.  If length == 1 at the default:, the
> code will absolutely do the right thing.
>
> Prove me wrong.

Thinking about a malformed tcp segment, which has no data but silly
options, and whose last byte is neither TCPOPT_EOL or TCPOPT_NOP, we
will try to dereference one byte over the boundary when parsing the
options. I know we have skb_shared_info at the end and it won't cause
any crash, but should we rely on this fact?

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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