Re: [patch 1/2] [RFC] Simple tamper-proof device filesystem.

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Pavel Emelyanov (xemul@openvz.org):
> Oren Laadan wrote:
> > 
> > Serge E. Hallyn wrote:
> >> Quoting Pavel Emelyanov (xemul@openvz.org):
> >>> Oren Laadan wrote:
> >>>> Serge E. Hallyn wrote:
> >>>>> Quoting Oren Laadan (orenl@cs.columbia.edu):
> >>>>>> 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 ?
> >>>>> Miklos' user mount patches enforced that if !capable(CAP_MKNOD),
> >>>>> then mnt->mnt_flags |= MNT_NODEV.  So that's no problem.
> >>>> Yes, that works to disallow all device files from a mounted file system.
> >>>>
> >>>> But it's a black and white thing: either they are all banned or allowed;
> >>>> you can't have some devices allowed and others not, depending on type
> >>>> A scenario where this may be useful is, for instance, if we some apps in
> >>>> the container to execute withing a pre-made chroot (sub)tree within that
> >>>> container.
> >>>>
> >>>>> But that's been pulled out of -mm! ?  Crap.
> >>>>>
> >>>>>> 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.
> >>>>> By that you mean more along the lines of Pavel's patch than my whitelist
> >>>>> LSM, or you actually mean Tetsuo's filesystem (i assume you don't mean that
> >>>>> by 'vfs layer' :), or something different entirely?
> >>>> :)
> >>>>
> >>>> By 'vfs' I mean at open() time, and not at mount(), or mknod() time.
> >>>> Either yours or Pavel's; I tend to prefer not to use LSM as it may
> >>>> collide with future security modules.
> >>> Oren, AFAIS you've seen my patches for device access controller, right?
> > 
> > If you mean this one:
> > http://openvz.org/pipermail/devel/2007-September/007647.html
> > then ack :)
> 
> Great! Thanks.
> 
> >>> Maybe we can revisit the issue then and try to come to agreement on what
> >>> kind of model and implementation we all want?
> >> That would be great, Pavel.  I do prefer your solution over my LSM, so
> >> if we can get an elegant block device control right in the vfs code that
> >> would be my preference.
> > 
> > I concur.
> > 
> > So it seems to me that we are all in favor of the model where open()
> > of a device will consult a black/white-list. Also, we are all in favor
> > of a non-LSM implementation, Pavel's code being a good example.
> 
> Thank you, Oren and Serge! I will revisit this issue then, but
> I have a vacation the next week and, after this, we have a New
> Year and Christmas holidays in Russia. So I will be able to go
> on with it only after the 7th January :( Hope this is OK for you.
> 
> Besides, Andrew told that he would pay little attention to new
> features till the 2.6.24 release, so I'm afraid we won't have this 
> even in -mm in the nearest months :(
> 
> Thanks,
> Pavel

Cool, let me know any way I can help when you get started.

thanks,
-serge