From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?UTF-8?Q?Am=C3=A9rico_Wang?= <xiyou.wangcong@gmail.com>
Subject: Re: [PATCH] AF_UNIX: Fix deadlock on connecting to shutdown socket
Date: Mon, 19 Oct 2009 17:06:08 +0800
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To: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
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On Mon, Oct 19, 2009 at 4:58 PM, Tomoki Sekiyama
<tomoki.sekiyama.qu@hitachi.com> wrote:
> Hi, thanks for testing!
>
> Am=C3=A9rico Wang wrote:
>> On Mon, Oct 19, 2009 at 2:02 PM, Tomoki Sekiyama
>> <tomoki.sekiyama.qu@hitachi.com> wrote:
>>> Hi,
>>> I found a deadlock bug in UNIX domain socket, which makes able to D=
oS
>>> attack against the local machine by non-root users.
>>>
>>> How to reproduce:
>>> 1. Make a listening AF_UNIX/SOCK_STREAM socket with an abstruct
>>> =C2=A0 =C2=A0namespace(*), and shutdown(2) it.
>>> =C2=A02. Repeat connect(2)ing to the listening socket from the othe=
r sockets
>>> =C2=A0 =C2=A0until the connection backlog is full-filled.
>>> =C2=A03. connect(2) takes the CPU forever. If every core is taken, =
the
>>> =C2=A0 =C2=A0system 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 $(grep processor -c /proc/cpuinfo)`;
>> do ./unix-socket-dos-exploit; echo "=3D=3D=3D=3D=3D$i=3D=3D=3D=3D";d=
one
> <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!