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

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Message-ID: <CAEivzxeQGkemxVwJ148b_+OmntUAWkdL==yMiTMN+GPyaLkFPg@mail.gmail.com>
Date:   Mon, 26 Jun 2023 13:23:16 +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 Mon, Jun 26, 2023 at 4:12 AM Xiubo Li <xiubli@...hat.com> wrote:
>
>
> On 6/24/23 15:11, Aleksandr Mikhalitsyn wrote:
> > 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?

Hi Xiubo,

>
> There is another way:
>
> For each client it will have a dedicated client auth caps, something like:
>
> client.foo
>    key: *key*
>    caps: [mds] allow r, allow rw path=/bar
>    caps: [mon] allow r
>    caps: [osd] allow rw tag cephfs data=cephfs_a

Do we have any infrastructure to get this caps list on the client side
right now?
(I've taken a quick look through the code and can't find anything
related to this.)

>
> When mounting this client with idmap enabled, then we can just check the
> above [mds] caps, if there has any UID/GID based permissions set, then
> fail the mounting.

understood

>
> That means this kind client couldn't be mounted with idmap enabled.
>
> Also we need to make sure that once there is a mount with idmap enabled,
> the corresponding client caps couldn't be append the UID/GID based
> permissions. This need a patch in ceph anyway IMO.

So, yeah we will need to effectively block cephx permission changes if
there is a client mounted with
an active idmapped mount. Sounds as something that require massive
changes on the server side.

At the same time this will just block users from using idmapped mounts
along with UID/GID restrictions.

If you want me to change server-side anyways, isn't it better just to
extend cephfs protocol to properly
handle UID/GIDs with idmapped mounts? (It was originally proposed by Christian.)
What we need to do here is to add a separate UID/GID fields for ceph
requests those are creating a new inodes
(like mknod, symlink, etc).

Kind regards,
Alex

>
> Thanks
>
> - Xiubo
>
>
>
>
>
> >
> > Thanks,
> > Alex
> >
> >> Thanks
> >>
> >> - Xiubo
> >>
>