linux-kernel - Re: [REVIEW][PATCH] vfs: Lock in place mounts from more privileged users

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Date:	Wed, 24 Jul 2013 08:46:45 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linux Containers <containers@...ts.linux-foundation.org>,
	"Serge E. Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [REVIEW][PATCH] vfs: Lock in place mounts from more privileged users

On Tue, Jul 23, 2013 at 11:50 PM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
> Andy Lutomirski <luto@...capital.net> writes:
>> On Tue, Jul 23, 2013 at 11:30 AM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>>
>>> When creating a less privileged mount namespace or propogating mounts
>>> from a more privileged to a less privileged mount namespace lock the
>>> submounts so they may not be unmounted individually in the child mount
>>> namespace revealing what is under them.
>>
>> I would propose a different rule: if vfsmount b is mounted on vfsmount
>> a, then to unmount b, you must be ns_capable(CAP_SYS_MOUNT) on either
>> a's namespace or b's namespace.  The idea is that you should be able
>> to see under a mount if you own the parent (because it's yours) or if
>> you own the child (because you, or someone no more privileged than
>> you, put it there).  This may result in a simpler patch and should do
>> much the same thing.
>
> It definitely won't result in a simpler patch as the information you are
> basing the decision on is not available.
>

Ah, I see -- mnt_ns gets changed when the namespace is duplicated.

Acked-by: Andy Lutomirski <luto@...capital.net>

--Andy
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