Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Gabriel Krisman Bertazi <krisman@suse.de>
To:     Andres Freund <andres@anarazel.de>
Cc:     Jeff Moyer <jmoyer@redhat.com>,
        Matteo Rizzo <matteorizzo@google.com>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        io-uring@vger.kernel.org, axboe@kernel.dk, asml.silence@gmail.com,
        corbet@lwn.net, akpm@linux-foundation.org, keescook@chromium.org,
        ribalda@chromium.org, rostedt@goodmis.org, jannh@google.com,
        chenhuacai@kernel.org, gpiccoli@igalia.com, ldufour@linux.ibm.com,
        evn@google.com, poprdi@google.com, jordyzomer@google.com
Subject: Re: [PATCH v3 1/1] io_uring: add a sysctl to disable io_uring
 system-wide
In-Reply-To: <20230809150945.abp755qafjhxbmx6@awork3.anarazel.de> (Andres
        Freund's message of "Wed, 9 Aug 2023 08:09:45 -0700")
References: <20230630151003.3622786-1-matteorizzo@google.com>
        <20230630151003.3622786-2-matteorizzo@google.com>
        <20230726174549.cg4jgx2d33fom4rb@awork3.anarazel.de>
        <x49fs5awiel.fsf@segfault.boston.devel.redhat.com>
        <20230809150945.abp755qafjhxbmx6@awork3.anarazel.de>
Date:   Wed, 09 Aug 2023 14:38:14 -0400
Message-ID: <87o7jg6oyx.fsf@suse.de>
User-Agent: Gnus/5.13 (Gnus v5.13)
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Andres Freund <andres@anarazel.de> writes:

> Hi,
>
> Sorry for the delayed response, EINBOXOVERFLOW.
>
> On 2023-07-26 16:02:26 -0400, Jeff Moyer wrote:
>> Andres Freund <andres@anarazel.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