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Date: Fri, 20 Apr 2012 11:23:57 +0400
From: Pavel Emelyanov <>
To: "Eric W. Biederman" <>
CC: Eugene Teo <>, Marcus Meissner <>,
        OSS Security List <>,
        "" <>,
        Sukadev Bhattiprolu <>,
        Serge Hallyn <>
Subject: Re: CVE request: pid namespace leak in kernel 3.0 and 3.1

On 04/20/2012 11:20 AM, Eric W. Biederman wrote:
> Pavel Emelyanov <> 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.

I'm talking about the call to pid_ns_prepare_proc which does kern_mount
thus bringing the proc sb in memory and pinning the init's pid on it.

> 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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