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

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Date:   Wed, 9 Aug 2023 08:09:45 -0700
From:   Andres Freund <andres@...razel.de>
To:     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,
        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,
        krisman@...e.de
Subject: Re: [PATCH v3 1/1] io_uring: add a sysctl to disable io_uring
 system-wide

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.

Greetings,

Andres Freund