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

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Date:	Mon, 19 Oct 2009 17:06:08 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	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

On Mon, Oct 19, 2009 at 4:58 PM, Tomoki Sekiyama
<tomoki.sekiyama.qu@...achi.com> wrote:
> 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).

Hmm, you are right.

My system hangs for 10 or more seconds after I did what you said.
Confirmed.

Thanks!
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