Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <0a42c5d0-0479-e60e-ac84-be3b915c62d9@redhat.com>
Date:   Tue, 4 Jul 2023 09:08:46 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.11.0
From:   Xiubo Li <xiubli@redhat.com>
Subject: Re: [PATCH v5 00/14] ceph: support idmapped mounts
To:     Aleksandr Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Cc:     Gregory Farnum <gfarnum@redhat.com>,
        Christian Brauner <brauner@kernel.org>, stgraber@ubuntu.com,
        linux-fsdevel@vger.kernel.org, Ilya Dryomov <idryomov@gmail.com>,
        Jeff Layton <jlayton@kernel.org>, ceph-devel@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20230608154256.562906-1-aleksandr.mikhalitsyn@canonical.com>
 <f3864ed6-8c97-8a7a-f268-dab29eb2fb21@redhat.com>
 <CAEivzxcRsHveuW3nrPnSBK6_2-eT4XPvza3kN2oogvnbVXBKvQ@mail.gmail.com>
 <20230609-alufolie-gezaubert-f18ef17cda12@brauner>
 <CAEivzxc_LW6mTKjk46WivrisnnmVQs0UnRrh6p0KxhqyXrErBQ@mail.gmail.com>
 <ac1c6817-9838-fcf3-edc8-224ff85691e0@redhat.com>
 <CAJ4mKGby71qfb3gd696XH3AazeR0Qc_VGYupMznRH3Piky+VGA@mail.gmail.com>
 <977d8133-a55f-0667-dc12-aa6fd7d8c3e4@redhat.com>
 <CAEivzxcr99sERxZX17rZ5jW9YSzAWYvAjOOhBH+FqRoso2=yng@mail.gmail.com>
 <626175e2-ee91-0f1a-9e5d-e506aea366fa@redhat.com>
 <64241ff0-9af3-6817-478f-c24a0b9de9b3@redhat.com>
 <CAEivzxeF51ZEKhQ-0M35nooZ7_cZgk1-q75-YbkeWpZ9RuHG4A@mail.gmail.com>
 <4c4f73d8-8238-6ab8-ae50-d83c1441ac05@redhat.com>
 <CAEivzxeQGkemxVwJ148b_+OmntUAWkdL==yMiTMN+GPyaLkFPg@mail.gmail.com>
Content-Language: en-US
In-Reply-To: <CAEivzxeQGkemxVwJ148b_+OmntUAWkdL==yMiTMN+GPyaLkFPg@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

Sorry, not sure, why my last reply wasn't sent out.

Do it again.


On 6/26/23 19:23, Aleksandr Mikhalitsyn wrote:
> On Mon, Jun 26, 2023 at 4:12 AM Xiubo Li<xiubli@redhat.com>  wrote:
>> On 6/24/23 15:11, Aleksandr Mikhalitsyn wrote:
>>> On Sat, Jun 24, 2023 at 3:37 AM Xiubo Li<xiubli@redhat.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 am afraid there is no.

But just after the following ceph PR gets merged it will be easy to do this:

https://github.com/ceph/ceph/pull/48027

This is still under testing.

>> 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.

Maybe no need much, it should be simple IMO. But I am not 100% sure.

> 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).

BTW, could you explain it more ? How could this resolve the issue we are 
discussing here ?

Thanks

- Xiubo


>
> Kind regards,
> Alex
>
>> Thanks
>>
>> - Xiubo
>>
>>
>>
>>
>>
>>> Thanks,
>>> Alex
>>>
>>>> Thanks
>>>>
>>>> - Xiubo
>>>>