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

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Date:   Wed, 21 Feb 2018 19:58:53 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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>,
        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

> 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!

How are you envisioning this rate-limiting to be implemented? Are
you going to fail an EFI call if the rate is too high?  I'm thinking that
we just add a delay to each call so that we can't exceed the limit.
That means your kernel install will complete, just slower than it
would without the delays.

I think I want a small random delay anyway to prevent users from
causing an SMI at the precise moment of their choosing.

-Tony