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Date:   Wed, 21 Feb 2018 10:21:04 -0800
From:   Andi Kleen <ak@linux.intel.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        "Luck, Tony" <tony.luck@intel.com>,
        Joe Konno <joe.konno@linux.intel.com>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Matthew Garrett <matthew.garrett@nebula.com>,
        Jeremy Kerr <jk@ozlabs.org>,
        Matthew Garrett <mjg59@google.com>,
        Peter Jones <pjones@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        James Bottomley <james.bottomley@hansenpartnership.com>
Subject: Re: [PATCH 1/2] fs/efivarfs: restrict inode permissions
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> 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.

-Andi