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

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Message-ID: <1453990063.7627.34.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 28 Jan 2016 06:07:43 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Zhouyi Zhou <yizhouzhou@....ac.cn>
Cc:	Zhouyi Zhou <zhouzhouyi@...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.org
Subject: Re: Re: [PATCH V2] netfilter: h323: avoid potential attack

On Thu, 2016-01-28 at 06:00 -0800, Eric Dumazet wrote:
> On Thu, 2016-01-28 at 21:14 +0800, Zhouyi Zhou wrote:
> 
> > My patch is intend to prevent kernel panic, to prevent reading garbage
> > or read data from a prior frame and leak secrets, the prototypes of the 
> > get_h2x5_addr functions and the functions that call get_h2x5_addr should
> > be changed, should we do this? 
> 
> In term of security, panics are better than allowing attacker to read
> data from other people, like a password.
> 
> BTW, are you able to trigger any panic ?
> 
> I am not familiar with this code, it is not obvious.
> 
> If a fix is needed, better doing it right.
> 


BTW, this module is protected by a lock (nf_h323_lock)

So adding a variable like 'h323_buffer_valid_bytes' that would contain
the number of valid bytes would not require to change prototypes.

This variable would be written when skb_header_pointer() is used in
get_tpkt_data() / get_udp_data()