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

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Date:   Wed, 9 Aug 2023 10:45:36 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Andres Freund <andres@...razel.de>, Jeff Moyer <jmoyer@...hat.com>
Cc:     Matteo Rizzo <matteorizzo@...gle.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, io-uring@...r.kernel.org,
        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, krisman@...e.de
Subject: Re: [PATCH v3 1/1] io_uring: add a sysctl to disable io_uring
 system-wide

On 8/9/23 9:09 AM, Andres Freund wrote:
> 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.

I'm going to drop the original patch until we work out a scheme that
everybody is happy with, and that is flexible enough.

-- 
Jens Axboe