linux-kernel - Re: [PATCH 1/2] fs/efivarfs: restrict inode permissions

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Date:   Wed, 21 Feb 2018 11:47:32 -0800
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Joe Konno <joe.konno@...ux.intel.com>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matthew Garrett <matthew.garrett@...ula.com>,
        Jeremy Kerr <jk@...abs.org>,
        Matthew Garrett <mjg59@...gle.com>,
        Peter Jones <pjones@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        James Bottomley <james.bottomley@...senpartnership.com>
Subject: Re: [PATCH 1/2] fs/efivarfs: restrict inode permissions

On Wed, Feb 21, 2018 at 10:21:04AM -0800, Andi Kleen wrote:
> > But it should be fairly easy to just add a 'struct ratelimit_state' to
> > 'struct user_struct', and then you can easily just use
> > 
> >    '&file->f_cred->user->ratelimit'
> > 
> > and you're done. Make sure the initial root user has it unlimited, and
> > limit it to something reasonable for all other user allocations.
> 
> How about uid name spaces? Someone untrusted in a container could 
> create a lot of uids and switch between them.
> 
> A global rate limit seems better. While in theory it allows DoS
> it's probably not worse than a lot of others we have with
> other resources, and it's relatively harmless.

The EFI calls are all about checking system configuration. A thing
that only a handful of users do on a very occasional basis. I don't
see much harm if my "efibootmgr -v" call is slowed down a bit (or even
a lot) because you are using a bunch of the available ratelimit reading
the efivars.

Per-user seems over engineered to solve this problem.

-Tony