netdev - Re: [PATCH] AF_UNIX: Fix deadlock on connecting to shutdown socket

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Date:	Mon, 19 Oct 2009 17:58:05 +0900
From:	Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com>
To:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Cc:	alan@...rguk.ukuu.org.uk, davem@...emloft.net,
	satoshi.oshima.fk@...achi.com, hidehiro.kawai.ez@...achi.com,
	hideo.aoki.tk@...achi.com, masanori.yoshida.tv@...achi.com
Subject: Re: [PATCH] AF_UNIX: Fix deadlock on connecting to shutdown socket

Hi, thanks for testing!

Américo Wang wrote:
> On Mon, Oct 19, 2009 at 2:02 PM, Tomoki Sekiyama
> <tomoki.sekiyama.qu@...achi.com> wrote:
>> Hi,
>> I found a deadlock bug in UNIX domain socket, which makes able to DoS
>> attack against the local machine by non-root users.
>>
>> How to reproduce:
>> 1. Make a listening AF_UNIX/SOCK_STREAM socket with an abstruct
>>    namespace(*), and shutdown(2) it.
>>  2. Repeat connect(2)ing to the listening socket from the other sockets
>>    until the connection backlog is full-filled.
>>  3. connect(2) takes the CPU forever. If every core is taken, the
>>    system hangs.
>>
>> PoC code: (Run as many times as cores on SMP machines.)

Sorry for my ambiguous explanation ...

> Interesting...
> 
> I tried this with the following command:
> 
> % for i in `seq 1 $(grep processor -c /proc/cpuinfo)`;
> do ./unix-socket-dos-exploit; echo "=====$i====";done
<snip>
> My system doesn't hang at all.
> 
> Am I missing something?
>
> Thanks!

You should run the ./unix-socket-dos-exploit concurrently, like below:

for i in {1..4} ; do ./unix-socket-dos-exploit & done

# For safety reason, the PoC code stops in 15 seconds by alarm(15).

-- 
Tomoki Sekiyama
Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: tomoki.sekiyama.qu@...achi.com

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