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

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

[Zhouyi Zhou]

Thanks Eric for replying
> -----Original Messages-----
> From: "Eric Dumazet" <eric.dumazet@gmail.com>
> Sent Time: Thursday, January 28, 2016
> To: "Zhouyi Zhou" <zhouzhouyi@gmail.com>
> Cc: pablo@netfilter.org, kaber@trash.net, kadlec@blackhole.kfki.hu, davem@davemloft.net, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.or, "Zhouyi Zhou" <yizhouzhou@ict.ac.cn>
> Subject: Re: [PATCH V2] netfilter: h323: avoid potential attack
> 
> On Thu, 2016-01-28 at 16:59 +0800, Zhouyi Zhou 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;
> > 
> > Signed-off-by: Zhouyi Zhou <yizhouzhou@ict.ac.cn>
> > ---
> 
> Except you did not address my feedback about potentially reading not
> initialized memory.
> 
> if the frame length was 1000 bytes, then surely accessing memory at
> offset 8000 will either read garbage, or read data from a prior frame
> and leak secrets.
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? 
> 
> 
> 
Cheers 
Zhouyi

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

[Eric Dumazet]

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.

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

[Eric Dumazet]

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()

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

[One Thousand Gnomes]

On Thu, 28 Jan 2016 06:00:50 -0800
Eric Dumazet <eric.dumazet@gmail.com> 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 ?

We have a smattering of panics in this code in bugzilla going back years.

https://bugzilla.kernel.org/show_bug.cgi?id=12473

etc

Alan

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

[Zhouyi Zhou]

Thanks for your advices.
I will take your advice if I could have the opportunity
to write the final code.

As matter of factor, I trigger this bug when I tried to 
migrate H323 code to other operating systems.

This could trigger a panic because get_h2x5_addr functions
is the first time we ever try to ask for potentially
out of range data because of H323 style decodings 
(the value taddr->ipAddress.ip is decoded in the midway between
calling skb_header_pointer and calling get_h2x5_addr)



> -----Original Messages-----
> From: "Florian Westphal" <fw@strlen.de>
> Sent Time: Thursday, January 28, 2016
> To: "Zhouyi Zhou" <zhouzhouyi@gmail.com>
> Cc: eric.dumazet@gmail.com, pablo@netfilter.org, kaber@trash.net, kadlec@blackhole.kfki.hu, davem@davemloft.net, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.or, "Zhouyi Zhou" <yizhouzhou@ict.ac.cn>
> Subject: Re: [PATCH V2] netfilter: h323: avoid potential attack
> 
> Zhouyi Zhou <zhouzhouyi@gmail.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).
>