linux-kernel - Re: [PATCH 1/1] Add a new sysctl to disable io

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Date:   Wed, 28 Jun 2023 11:59:25 -0400
From:   Jeff Moyer <jmoyer@...hat.com>
To:     Gabriel Krisman Bertazi <krisman@...e.de>
Cc:     Matteo Rizzo <matteorizzo@...gle.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, io-uring@...r.kernel.org,
        jordyzomer@...gle.com, evn@...gle.com, poprdi@...gle.com,
        corbet@....net, axboe@...nel.dk, asml.silence@...il.com,
        akpm@...ux-foundation.org, keescook@...omium.org,
        rostedt@...dmis.org, dave.hansen@...ux.intel.com,
        ribalda@...omium.org, chenhuacai@...nel.org, steve@....org,
        gpiccoli@...lia.com, ldufour@...ux.ibm.com
Subject: Re: [PATCH 1/1] Add a new sysctl to disable io_uring system-wide

Gabriel Krisman Bertazi <krisman@...e.de> writes:

> Matteo Rizzo <matteorizzo@...gle.com> writes:
>
>> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
>> index d85d90f5d000..3c53a238332a 100644
>> --- a/Documentation/admin-guide/sysctl/kernel.rst
>> +++ b/Documentation/admin-guide/sysctl/kernel.rst
>> @@ -450,6 +450,20 @@ this allows system administrators to override the
>>  ``IA64_THREAD_UAC_NOPRINT`` ``prctl`` and avoid logs being flooded.
>>  
>>  
>> +io_uring_disabled
>> +=========================
>> +
>> +Prevents all processes from creating new io_uring instances. Enabling this
>> +shrinks the kernel's attack surface.
>> +
>> += =============================================================
>> +0 All processes can create io_uring instances as normal. This is the default
>> +  setting.
>> +1 io_uring is disabled. io_uring_setup always fails with -EPERM. Existing
>> +  io_uring instances can still be used.
>> += =============================================================
>
> I had an internal request for something like this recently.  If we go
> this route, we could use a intermediary option that limits io_uring
> to root processes only.

This is all regrettable, but this option makes the most sense to me.
Testing for CAP_SYS_ADMIN or CAP_SYS_RAW_IO would work for that third
option, I think.

-Jeff