linux-kernel - Re: [PATCH v4] io_uring: add a sysctl to disable io

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Message-ID: <87cyzm504h.fsf@suse.de>
Date:   Wed, 16 Aug 2023 14:10:38 -0400
From:   Gabriel Krisman Bertazi <krisman@...e.de>
To:     Jeff Moyer <jmoyer@...hat.com>
Cc:     matteorizzo@...gle.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, io-uring@...r.kernel.org,
        axboe@...nel.dk, asml.silence@...il.com, corbet@....net,
        akpm@...ux-foundation.org, keescook@...omium.org,
        ribalda@...omium.org, rostedt@...dmis.org, jannh@...gle.com,
        chenhuacai@...nel.org, gpiccoli@...lia.com, ldufour@...ux.ibm.com,
        evn@...gle.com, poprdi@...gle.com, jordyzomer@...gle.com,
        andres@...razel.de
Subject: Re: [PATCH v4] io_uring: add a sysctl to disable io_uring system-wide

Jeff Moyer <jmoyer@...hat.com> writes:

> From: Matteo Rizzo <matteorizzo@...gle.com>
>
> Introduce a new sysctl (io_uring_disabled) which can be either 0, 1, or
> 2. When 0 (the default), all processes are allowed to create io_uring
> instances, which is the current behavior.  When 1, io_uring creation is
> disabled (io_uring_setup() will fail with -EPERM) for processes not in
> the kernel.io_uring_group group.  When 2, calls to io_uring_setup() fail
> with -EPERM regardless of privilege.
>
> Signed-off-by: Matteo Rizzo <matteorizzo@...gle.com>
> [JEM: modified to add io_uring_group]
> Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
>
> ---
> v4:
>
> * Add a kernel.io_uring_group sysctl to hold a group id that is allowed
>   to use io_uring.  One thing worth pointing out is that, when a group
>   is specified, only users in that group can create an io_uring.  That
>   means that if the root user is not in that group, root can not make
>   use of io_uring.

Rejecting root if it's not in the group doesn't make much sense to
me. Of course, root can always just add itself to the group, so it is
not a security feature. But I'd expect 'sudo <smth>' to not start giving
EPERM based on user group settings.  Can you make CAP_SYS_ADMIN
always allowed for option 1?

>   I also wrote unit tests for liburing.  I'll post that as well if there
>   is consensus on this approach.

I'm fine with this approach as it allow me to easily reject non-root users.

-- 
Gabriel Krisman Bertazi