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

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Date:   Wed, 21 Feb 2018 11:50:25 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        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 11:47 AM, Luck, Tony <tony.luck@...el.com> wrote:
>
> 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.
>

It's not about slowing down.

It's about "user Xyz is messing with the system and reading efi vars
all the time" resulting in "user 'torvalds' is installing a kernel,
and actually wants to read efi vars, but can't".

if you don't make it per-user, you're just replacing one DoS attack
with another one!

               Linus