linux-kernel - Re: [PATCH v3 1/1] io_uring: add a sysctl to disable io

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Date:   Wed, 09 Aug 2023 14:38:14 -0400
From:   Gabriel Krisman Bertazi <krisman@...e.de>
To:     Andres Freund <andres@...razel.de>
Cc:     Jeff Moyer <jmoyer@...hat.com>,
        Matteo Rizzo <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
Subject: Re: [PATCH v3 1/1] io_uring: add a sysctl to disable io_uring
 system-wide

Andres Freund <andres@...razel.de> writes:

> Hi,
>
> Sorry for the delayed response, EINBOXOVERFLOW.
>
> On 2023-07-26 16:02:26 -0400, Jeff Moyer wrote:
>> Andres Freund <andres@...razel.de> writes:
>> 
>> > Hi,
>> >
>> > On 2023-06-30 15:10:03 +0000, Matteo Rizzo wrote:
>> >> 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, all calls to
>> >> io_uring_setup fail with -EPERM unless the calling process has
>> >> CAP_SYS_ADMIN. When 2, calls to io_uring_setup fail with -EPERM
>> >> regardless of privilege.
>> >
>> > Hm, is there a chance that instead of requiring CAP_SYS_ADMIN, a certain group
>> > could be required (similar to hugetlb_shm_group)? Requiring CAP_SYS_ADMIN
>> > could have the unintended consequence of io_uring requiring tasks being run
>> > with more privileges than needed... Or some other more granular way of
>> > granting the right to use io_uring?
>> 
>> That's fine with me, so long as there is still an option to completely
>> disable io_uring.
>
> Makes sense.
>
>
>> > ISTM that it'd be nice if e.g. a systemd service specification could allow
>> > some services to use io_uring, without allowing it for everyone, or requiring
>> > to run services effectively as root.
>> 
>> Do you have a proposal for how that would work?
>
> I think group based permissions would allow for it, even if perhaps not in the
> most beautiful manner. Systemd can configure additional groups for a service
> with SupplementaryGroups, so adding a "io_uring" group or such should
> work.

This is more complex/requires more configuration than just blocking
root/non-root. Also, might not be practical for non-systemd systems, I
suspect. Can we keep the other options in the sysctl io_uring_disabled
as well:

0 -> all allowed (default)
1 -> group based permission
2 -> root only
3 -> all blocked

-- 
Gabriel Krisman Bertazi