linux-kernel - Re: [PATCH v9 03/12] ceph: handle idmapped mounts in create_request

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Date:   Fri, 4 Aug 2023 16:53:02 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
Cc:     xiubli@...hat.com, stgraber@...ntu.com,
        linux-fsdevel@...r.kernel.org, Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 03/12] ceph: handle idmapped mounts in
 create_request_message()

On Fri, Aug 04, 2023 at 10:48:49AM +0200, Alexander Mikhalitsyn wrote:
> From: Christian Brauner <brauner@...nel.org>
> 
> Inode operations that create a new filesystem object such as ->mknod,
> ->create, ->mkdir() and others don't take a {g,u}id argument explicitly.
> Instead the caller's fs{g,u}id is used for the {g,u}id of the new
> filesystem object.
> 
> In order to ensure that the correct {g,u}id is used map the caller's
> fs{g,u}id for creation requests. This doesn't require complex changes.
> It suffices to pass in the relevant idmapping recorded in the request
> message. If this request message was triggered from an inode operation
> that creates filesystem objects it will have passed down the relevant
> idmaping. If this is a request message that was triggered from an inode
> operation that doens't need to take idmappings into account the initial
> idmapping is passed down which is an identity mapping.
> 
> This change uses a new cephfs protocol extension CEPHFS_FEATURE_HAS_OWNER_UIDGID
> which adds two new fields (owner_{u,g}id) to the request head structure.
> So, we need to ensure that MDS supports it otherwise we need to fail
> any IO that comes through an idmapped mount because we can't process it
> in a proper way. MDS server without such an extension will use caller_{u,g}id
> fields to set a new inode owner UID/GID which is incorrect because caller_{u,g}id
> values are unmapped. At the same time we can't map these fields with an
> idmapping as it can break UID/GID-based permission checks logic on the
> MDS side. This problem was described with a lot of details at [1], [2].
> 
> [1] https://lore.kernel.org/lkml/CAEivzxfw1fHO2TFA4dx3u23ZKK6Q+EThfzuibrhA3RKM=ZOYLg@mail.gmail.com/
> [2] https://lore.kernel.org/all/20220104140414.155198-3-brauner@kernel.org/
> 
> Link: https://github.com/ceph/ceph/pull/52575
> Link: https://tracker.ceph.com/issues/62217
> Cc: Xiubo Li <xiubli@...hat.com>
> Cc: Jeff Layton <jlayton@...nel.org>
> Cc: Ilya Dryomov <idryomov@...il.com>
> Cc: ceph-devel@...r.kernel.org
> Co-Developed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> Signed-off-by: Christian Brauner <brauner@...nel.org>
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> ---

I like the new extension,
Acked-by: Christian Brauner <brauner@...nel.org>