linux-kernel - Re: [patch 8/9] unprivileged mounts: propagation: inherit owner from parent

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Message-ID: <20080115142115.GC4453@sergelap.austin.ibm.com>
Date:	Tue, 15 Jan 2008 08:21:15 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	serue@...ibm.com, akpm@...ux-foundation.org, hch@...radead.org,
	viro@....linux.org.uk, ebiederm@...ssion.com, kzak@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, util-linux-ng@...r.kernel.org
Subject: Re: [patch 8/9] unprivileged mounts: propagation: inherit owner
	from parent

Quoting Miklos Szeredi (miklos@...redi.hu):
> > Quoting Miklos Szeredi (miklos@...redi.hu):
> > > From: Miklos Szeredi <mszeredi@...e.cz>
> > > 
> > > On mount propagation, let the owner of the clone be inherited from the
> > > parent into which it has been propagated.  Also if the parent has the
> > > "nosuid" flag, set this flag for the child as well.
> > 
> > What about nodev?
> 
> Hmm, I think the nosuid thing is meant to prevent suid mounts being
> introduced into a "suidless" namespace.  This doesn't apply to dev
> mounts, which are quite safe in a suidless environment, as long as the
> user is not able to create devices.  But that should be taken care of
> by capability tests.
> 
> I'll update the description.

Hmm,

Part of me wants to say the safest thing for now would be to refuse
mounts propagation from non-user mounts to user mounts.

I assume you're thinking about a fully user-mounted chroot, where
the user woudl still want to be able to stick in a cdrom and have
it automounted under /mnt/cdrom, propagated from the root mounts ns?

But then are there no devices which the user could create on a floppy
while inserted into his own laptop, owned by his own uid, then insert
into this machine, and use the device under the auto-mounted /dev/floppy
to gain inappropriate access?

-serge
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