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

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Message-ID: <f885fddd-d511-0e31-cafe-b766144e6207@redhat.com>
Date:   Tue, 4 Jul 2023 09:10:22 +0800
From:   Xiubo Li <xiubli@...hat.com>
To:     Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@...onical.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 6/26/23 19:49, Aleksandr Mikhalitsyn wrote:
> On Mon, Jun 26, 2023 at 1:23 PM Aleksandr Mikhalitsyn
> <aleksandr.mikhalitsyn@...onical.com> wrote:
>> 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.)
> I've found your PR that looks related https://github.com/ceph/ceph/pull/48027

Yeah, after this we need to do some extra work in kclient and then it 
will be easy to check the caps I think.

Thanks

- Xiubo

>>> 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
>>>>>