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Message-ID: <m162cudg49.fsf@fess.ebiederm.org>
Date: Fri, 20 Apr 2012 00:20:06 -0700
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Pavel Emelyanov <xemul@...allels.com>
Cc: Eugene Teo <eugeneteo@...nel.sg>, Marcus Meissner <meissner@...e.de>, OSS Security List <oss-security@...ts.openwall.com>, "security\@kernel.org" <security@...nel.org>, Sukadev Bhattiprolu <sukadev@...ibm.com>, Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: CVE request: pid namespace leak in kernel 3.0 and 3.1
Pavel Emelyanov <xemul@...allels.com> writes:
> On 04/20/2012 07:10 AM, Eugene Teo wrote:
>>> So we know what is holding the pid namespace reference.
>>>
>>> Additional thoughts.
>>>
>>> Does echo 3 > /proc/sys/vm/drop_caches clear up the issue?
>>
>> No.
>>
>>> Is there a corresponding task_struct leak?
>>
>> Yes.
>>
>>> I don't have much of a clue or much concern as this seems fixed in later kernels but I am happy to suggest things to look for to help narrow this down.
>>
>> I'm helping to provide more information.
>
> Is there also a vfsmount struct leak as well? The pidns creating implies
> kern-mount-ing of a proc and it should be released when child reaper of
> the namespace dies.
In this case the user is vsftp which is an entertaining user.
Roughly for every connection vsftp does:
- accepts the connection
- forks a server process
- unshares the network ipc and pid namespaces for additional isolation
- drops privilegs?
- serves up the file.
Since vsftp does not want any of the features of namespaces it does not
setup mounts or any of that. vsftp simply wants a way to reduce the
the chance that a bug in the implemenation of vsftp will all the server
to be compromised.
To that extent I believe the reproduce program was very representative
of what vsftp is doing.
Eric
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