linux-kernel - Re: [PATCH v5 00/14] ceph: support idmapped mounts

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Message-ID: <CAEivzxeF51ZEKhQ-0M35nooZ7_cZgk1-q75-YbkeWpZ9RuHG4A@mail.gmail.com>
Date:   Sat, 24 Jun 2023 09:11:24 +0200
From:   Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     Gregory Farnum <gfarnum@...hat.com>,
        Christian Brauner <brauner@...nel.org>, stgraber@...ntu.com,
        linux-fsdevel@...r.kernel.org, Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 00/14] ceph: support idmapped mounts

On Sat, Jun 24, 2023 at 3:37 AM Xiubo Li <xiubli@...hat.com> wrote:
>
> [...]
>
>  > > >
>  > > > I thought about this too and came to the same conclusion, that
> UID/GID
>  > > > based
>  > > > restriction can be applied dynamically, so detecting it on mount-time
>  > > > helps not so much.
>  > > >
>  > > For this you please raise one PR to ceph first to support this, and in
>  > > the PR we can discuss more for the MDS auth caps. And after the PR
>  > > getting merged then in this patch series you need to check the
>  > > corresponding option or flag to determine whether could the idmap
>  > > mounting succeed.
>  >
>  > I'm sorry but I don't understand what we want to support here. Do we
> want to
>  > add some new ceph request that allows to check if UID/GID-based
>  > permissions are applied for
>  > a particular ceph client user?
>
> IMO we should prevent user to set UID/GID-based permisions caps from
> ceph side.
>
> As I know currently there is no way to prevent users to set MDS auth
> caps, IMO in ceph side at least we need one flag or option to disable
> this once users want this fs cluster sever for idmap mounts use case.

How this should be visible from the user side? We introducing a new
kernel client mount option,
like "nomdscaps", then pass flag to the MDS and MDS should check that
MDS auth permissions
are not applied (on the mount time) and prevent them from being
applied later while session is active. Like that?

At the same time I'm thinking about protocol extension that adds 2
additional fields for UID/GID. This will allow to correctly
handle everything. I wanted to avoid any changes to the protocol or
server-side things. But if we want to change MDS side,
maybe it's better then to go this way?

Thanks,
Alex

>
> Thanks
>
> - Xiubo
>