linux-kernel - Re: [Devel] Re: [patch 05/10] add "permit user mounts in new namespace" clone flag

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Date:	Wed, 18 Apr 2007 12:41:07 -0700
From:	Ram Pai <linuxram@...ibm.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	serue@...ibm.com, devel@...nvz.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, viro@....linux.org.uk,
	linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [Devel] Re: [patch 05/10] add "permit user mounts in new
	namespace" clone flag

On Wed, 2007-04-18 at 21:14 +0200, Miklos Szeredi wrote:
> > As I said earlier, I see a case where two mounts that are peers of each
> > other can become un-identical if we dont propagate the "allowusermnt".
> > 
> > As a practical example.
> > 
> > /tmp and /mnt are peers of each other.
> > /tmp has its "allowusermnt" flag set, which has not been propagated
> > to /mnt.
> > 
> > now a normal-user mounts an ext2 file system under /tmp at /tmp/1
> > 
> > unfortunately the mount wont appear under /mnt/1 
> 
> Argh, that is not true.  That's what I've been trying to explain to
> you all along.

I now realize you did, but I failed to catch it. sorry :-(

> 
> The propagation will be done _regardless_ of the flag.  The flag is
> only checked for the parent of the _requested_ mount.  If it is
> allowed there, the mount, including any propagations are allowed.  If
> it's denied, then obviously it's denied everywhere.
> 
> > and in case if you allow the mount to appear under /mnt/1, you will
> > break unpriviledge mounts semantics which promises: a normal user will
> > not be able to mount at a location that does not allow user-mounts.
> 
> No, it does not promise that.  The flag just promises, that the user
> cannot _request_ a mount on the parent mount.

ok. if the ability for a normal user to mount something *indirectly*
under a mount that has its 'allowusermnt flag' unset, 
is acceptable under the definition of 'allowusermnt', i guess my only
choice is to accept it. :-)

RP

> 
> Miklos

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