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SubjectRe: [PATCH v4] io_uring: add a sysctl to disable io_uring system-wide
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Jeff Moyer <jmoyer@redhat.com> writes:

> From: Matteo Rizzo <matteorizzo@google.com>
>
> 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, io_uring creation is
> disabled (io_uring_setup() will fail with -EPERM) for processes not in
> the kernel.io_uring_group group. When 2, calls to io_uring_setup() fail
> with -EPERM regardless of privilege.
>
> Signed-off-by: Matteo Rizzo <matteorizzo@google.com>
> [JEM: modified to add io_uring_group]
> Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
>
> ---
> v4:
>
> * Add a kernel.io_uring_group sysctl to hold a group id that is allowed
> to use io_uring. One thing worth pointing out is that, when a group
> is specified, only users in that group can create an io_uring. That
> means that if the root user is not in that group, root can not make
> use of io_uring.

Rejecting root if it's not in the group doesn't make much sense to
me. Of course, root can always just add itself to the group, so it is
not a security feature. But I'd expect 'sudo <smth>' to not start giving
EPERM based on user group settings. Can you make CAP_SYS_ADMIN
always allowed for option 1?

> I also wrote unit tests for liburing. I'll post that as well if there
> is consensus on this approach.

I'm fine with this approach as it allow me to easily reject non-root users.

--
Gabriel Krisman Bertazi

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