netdev - Re: [PATCH V2] netfilter: h323: avoid potential attack

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Message-ID: <20160128142959.GB30994@breakpoint.cc>
Date:	Thu, 28 Jan 2016 15:29:59 +0100
From:	Florian Westphal <fw@...len.de>
To:	Zhouyi Zhou <zhouzhouyi@...il.com>
Cc:	eric.dumazet@...il.com, pablo@...filter.org, kaber@...sh.net,
	kadlec@...ckhole.kfki.hu, davem@...emloft.net,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.or,
	Zhouyi Zhou <yizhouzhou@....ac.cn>
Subject: Re: [PATCH V2] netfilter: h323: avoid potential attack

Zhouyi Zhou <zhouzhouyi@...il.com> wrote:
> Thanks Eric for your review and advice.
> 
> I think hackers chould build a malicious h323 packet to overflow
> the pointer p which will panic during the memcpy(addr, p, len)
> 
> For example, he may fabricate a very large taddr->ipAddress.ip;

Can you be more specific?

h323_buffer is backend storage for skb_header_pointer, i.e.
this will error out early when we ask for more data than is available in
packet.

I don't understand how this could overflow anything.
Even assuming 64k packet we'd still have enough room in h323_buffer
for an ipv6 address, no? (we skip the l3/l4 header when extracting
packet payload).