I hate to bring this again, but what if the admin in the container
mounts an external file system (eg. nfs, usb, loop mount from a file,
or via fuse), and that file system already has a device that we would
like to ban inside that container ?

Since anyway we will have to keep a white- (or black-) list of devices
that are permitted in a container, and that list may change even change
per container -- why not enforce the access control at the VFS layer ?
It's safer in the long run.

Oren.

Serge E. Hallyn wrote:

Quoting Tetsuo Handa (penguin-kernel@i-love.sakura.ne.jp):

quoted

Hello.

Serge E. Hallyn wrote:

quoted

CAP_MKNOD will be removed from its capability

I think it is not enough because the root can rename/unlink device files
(mv /dev/sda1 /dev/tmp; mv /dev/sda2 /dev/sda1; mv /dev/tmp /dev/sda2).

Sure but that doesn't bother us :)

The admin in the container has his own /dev directory and can do what he
likes with the devices he's allowed to have.  He just shouldn't have
access to others.  If he wants to rename /dev/sda1 to /dev/sda5 that's
his choice.

quoted

quoted

To use your approach, i guess we would have to use selinux (or tomoyo)
to enforce that devices may only be created under /dev?

Everyone can use this filesystem alone.

Sure but it is worthless alone.

No?

What will keep the container admin from doing 'mknod /root/hda1 b 3 1'?

quoted

But use with MAC (or whatever access control mechanisms that prevent
attackers from unmounting/overlaying this filesystem) is recomennded.

-serge
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