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Date:   Tue, 12 Jan 2021 23:00:42 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org
Cc:     John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Geoffrey Thomas <geofft@...reload.com>,
        Mrunal Patel <mpatel@...hat.com>,
        Josh Triplett <josh@...htriplett.org>,
        Andy Lutomirski <luto@...nel.org>,
        Theodore Tso <tytso@....edu>, Alban Crequy <alban@...volk.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Howells <dhowells@...hat.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        Stéphane Graber <stgraber@...ntu.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Lennart Poettering <lennart@...ttering.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, smbarber@...omium.org,
        Phil Estes <estesp@...il.com>, Serge Hallyn <serge@...lyn.com>,
        Kees Cook <keescook@...omium.org>,
        Todd Kjos <tkjos@...gle.com>, Paul Moore <paul@...l-moore.com>,
        Jonathan Corbet <corbet@....net>,
        containers@...ts.linux-foundation.org,
        linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: [PATCH v5 00/42] idmapped mounts

Hey everyone,

The only major change is the inclusion of hch's patch to port XFS to
support idmapped mounts. Thanks to Christoph for doing that work.
(For a full list of major changes between versions see the end of this
 cover letter.
 Please also note the large xfstests testsuite in patch 42 that has been
 kept as part of this series. It verifies correct vfs behavior with and
 without idmapped mounts including covering newer vfs features such as
 io_uring.
 I currently still plan to target the v5.12 merge window.)

With this patchset we make it possible to attach idmappings to mounts,
i.e. simply put different bind mounts can expose the same file or
directory with different ownership.
Shifting of ownership on a per-mount basis handles a wide range of
long standing use-cases. Here are just a few:
- Shifting of a subset of ownership-less filesystems (vfat) for use by
  multiple users, effectively allowing for DAC on such devices
  (systemd, Android, ...)
- Allow remapping uid/gid on external filesystems or paths (USB sticks,
  network filesystem, ...) to match the local system's user and groups.
  (David Howells intends to port AFS as a first candidate.)
- Shifting of a container rootfs or base image without having to mangle
  every file (runc, Docker, containerd, k8s, LXD, systemd ...)
- Sharing of data between host or privileged containers with
  unprivileged containers (runC, Docker, containerd, k8s, LXD, ...)
- Data sharing between multiple user namespaces with incompatible maps
  (LXD, k8s, ...)

There has been significant interest in this patchset as evidenced by
user commenting on previous version of this patchset. They include
containerd, ChromeOS, systemd, LXD and a range of others. There is
already a patchset up for containerd, the default Kubernetes container
runtime https://github.com/containerd/containerd/pull/4734
to make use of this. systemd intends to use it in their systemd-homed
implementation for portable home directories. ChromeOS wants to make use
of it to share data between the host and the Linux containers they run
on Chrome- and Pixelbooks.
(Fwiw, for fun and since I wanted to do this for a long time I've ported
 my home directory to be completely portable with a simple service file
 that now mounts my home directory on an ext4 formatted usb stick with
 an id mapping mapping all files to the random uid I'm assigned at
 login.)

Making it possible to share directories and mounts between users with
different uids and gids is itself quite an important use-case in
distributed systems environments. It's of course especially useful in
general for portable usb sticks, sharing data between multiple users in,
and sharing home directories between multiple users. The last example is
now elegantly expressed in systemd's homed concept for portable home
directories. As mentioned above, idmapped mounts also allow data from
the host to be shared with unprivileged containers, between privileged
and unprivileged containers simultaneously and in addition also between
unprivileged containers with different idmappings whenever they are used
to isolate one container completely from another container.

We have implemented and proposed multiple solutions to this before. This
included the introduction of fsid mappings, a tiny filesystem I've
authored with Seth Forshee that is currently carried in Ubuntu that has
shown to be the wrong approach, and the conceptual hack of calling
override creds directly in the vfs. In addition, to some of these
solutions being hacky none of these solutions have covered all of the
above use-cases.

Idmappings become a property of struct vfsmount instead of tying it to a
process being inside of a user namespace which has been the case for all
other proposed approaches. It also allows to pass down the user
namespace into the filesystems which is a clean way instead of violating
calling conventions by strapping the user namespace information that is
a property of the mount to the caller's credentials or similar hacks.
Each mount can have a separate idmapping and idmapped mounts can even be
created in the initial user namespace unblocking a range of use-cases.

To this end the vfsmount struct gains a new struct user_namespace
member. The idmapping of the user namespace becomes the idmapping of the
mount. A caller that is privileged with respect to the user namespace of
the superblock of the underlying filesystem can create an idmapped
mount. In the future, we can enable unprivileged use-cases by checking
whether the caller is privileged wrt to the user namespace that an
already idmapped mount has been marked with, allowing them to change the
idmapping. For now, keep things simple until the need arises.
Note, that with syscall interception it is already possible to intercept
idmapped mount requests from unprivileged containers and handle them in
a sufficiently privileged container manager. Support for this is already
available in LXD and will be available in runC where syscall
interception is currently in the process of becoming part of the runtime
spec: https://github.com/opencontainers/runtime-spec/pull/1074.

The user namespace the mount will be marked with can be specified by
passing a file descriptor refering to the user namespace as an argument
to the new mount_setattr() syscall together with the new
MOUNT_ATTR_IDMAP flag. By default vfsmounts are marked with the initial
user namespace and no behavioral or performance changes are observed.
All mapping operations are nops for the initial user namespace. When a
file/inode is accessed through an idmapped mount the i_uid and i_gid of
the inode will be remapped according to the user namespace the mount has
been marked with.

In order to support idmapped mounts, filesystems need to be changed and
mark themselves with the FS_ALLOW_IDMAP flag in fs_flags. The initial
version contains fat, ext4, and xfs including a list of examples.
But patches for other filesystems are actively worked on and will be
sent out separately. We are here to see this through and there are
multiple people involved in converting filesystems. So filesystem
developers are not left alone with this and are provided with a large
testsuite to verify that their port is correct.

There is a simple tool available at
https://github.com/brauner/mount-idmapped that allows to create idmapped
mounts so people can play with this patch series. Here are a few
illustrations:

1. Create a simple idmapped mount of another user's home directory

u1001@...vm:/$ sudo ./mount-idmapped --map-mount b:1000:1001:1 /home/ubuntu/ /mnt
u1001@...vm:/$ ls -al /home/ubuntu/
total 28
drwxr-xr-x 2 ubuntu ubuntu 4096 Oct 28 22:07 .
drwxr-xr-x 4 root   root   4096 Oct 28 04:00 ..
-rw------- 1 ubuntu ubuntu 3154 Oct 28 22:12 .bash_history
-rw-r--r-- 1 ubuntu ubuntu  220 Feb 25  2020 .bash_logout
-rw-r--r-- 1 ubuntu ubuntu 3771 Feb 25  2020 .bashrc
-rw-r--r-- 1 ubuntu ubuntu  807 Feb 25  2020 .profile
-rw-r--r-- 1 ubuntu ubuntu    0 Oct 16 16:11 .sudo_as_admin_successful
-rw------- 1 ubuntu ubuntu 1144 Oct 28 00:43 .viminfo
u1001@...vm:/$ ls -al /mnt/
total 28
drwxr-xr-x  2 u1001 u1001 4096 Oct 28 22:07 .
drwxr-xr-x 29 root  root  4096 Oct 28 22:01 ..
-rw-------  1 u1001 u1001 3154 Oct 28 22:12 .bash_history
-rw-r--r--  1 u1001 u1001  220 Feb 25  2020 .bash_logout
-rw-r--r--  1 u1001 u1001 3771 Feb 25  2020 .bashrc
-rw-r--r--  1 u1001 u1001  807 Feb 25  2020 .profile
-rw-r--r--  1 u1001 u1001    0 Oct 16 16:11 .sudo_as_admin_successful
-rw-------  1 u1001 u1001 1144 Oct 28 00:43 .viminfo
u1001@...vm:/$ touch /mnt/my-file
u1001@...vm:/$ setfacl -m u:1001:rwx /mnt/my-file
u1001@...vm:/$ sudo setcap -n 1001 cap_net_raw+ep /mnt/my-file
u1001@...vm:/$ ls -al /mnt/my-file
-rw-rwxr--+ 1 u1001 u1001 0 Oct 28 22:14 /mnt/my-file
u1001@...vm:/$ ls -al /home/ubuntu/my-file
-rw-rwxr--+ 1 ubuntu ubuntu 0 Oct 28 22:14 /home/ubuntu/my-file
u1001@...vm:/$ getfacl /mnt/my-file
getfacl: Removing leading '/' from absolute path names
# file: mnt/my-file
# owner: u1001
# group: u1001
user::rw-
user:u1001:rwx
group::rw-
mask::rwx
other::r--
u1001@...vm:/$ getfacl /home/ubuntu/my-file
getfacl: Removing leading '/' from absolute path names
# file: home/ubuntu/my-file
# owner: ubuntu
# group: ubuntu
user::rw-
user:ubuntu:rwx
group::rw-
mask::rwx
other::r--

2. Create mapping of the whole ext4 rootfs without a mapping for uid and gid 0

ubuntu@...vm:~$ sudo /mount-idmapped --map-mount b:1:1:65536 / /mnt/
ubuntu@...vm:~$ findmnt | grep mnt
└─/mnt                                /dev/sda2  ext4       rw,relatime
  └─/mnt/mnt                          /dev/sda2  ext4       rw,relatime
ubuntu@...vm:~$ sudo mkdir /AS-ROOT-CAN-CREATE
ubuntu@...vm:~$ sudo mkdir /mnt/AS-ROOT-CANT-CREATE
mkdir: cannot create directory ‘/mnt/AS-ROOT-CANT-CREATE’: Value too large for defined data type
ubuntu@...vm:~$ mkdir /mnt/home/ubuntu/AS-USER-1000-CAN-CREATE

3. Create a vfat usb mount and expose to user 1001 and 5000

ubuntu@...vm:/$ sudo mount /dev/sdb /mnt
ubuntu@...vm:/$ findmnt  | grep mnt
└─/mnt                                /dev/sdb vfat       rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro
ubuntu@...vm:/$ ls -al /mnt
total 12
drwxr-xr-x  2 root root 4096 Jan  1  1970 .
drwxr-xr-x 34 root root 4096 Oct 28 22:24 ..
-rwxr-xr-x  1 root root    4 Oct 28 03:44 aaa
-rwxr-xr-x  1 root root    0 Oct 28 01:09 bbb
ubuntu@...vm:/$ sudo /mount-idmapped --map-mount b:0:1001:1 /mnt /mnt-1001/
ubuntu@...vm:/$ ls -al /mnt-1001/
total 12
drwxr-xr-x  2 u1001 u1001 4096 Jan  1  1970 .
drwxr-xr-x 34 root  root  4096 Oct 28 22:24 ..
-rwxr-xr-x  1 u1001 u1001    4 Oct 28 03:44 aaa
-rwxr-xr-x  1 u1001 u1001    0 Oct 28 01:09 bbb
ubuntu@...vm:/$ sudo /mount-idmapped --map-mount b:0:5000:1 /mnt /mnt-5000/
ubuntu@...vm:/$ ls -al /mnt-5000/
total 12
drwxr-xr-x  2 5000 5000 4096 Jan  1  1970 .
drwxr-xr-x 34 root root 4096 Oct 28 22:24 ..
-rwxr-xr-x  1 5000 5000    4 Oct 28 03:44 aaa
-rwxr-xr-x  1 5000 5000    0 Oct 28 01:09 bbb

4. Create an idmapped rootfs mount for a container

root@...vm:~# ls -al /var/lib/lxc/f2/rootfs/
total 68
drwxr-xr-x 17 20000 20000 4096 Sep 24 07:48 .
drwxrwx---  3 20000 20000 4096 Oct 16 19:26 ..
lrwxrwxrwx  1 20000 20000    7 Sep 24 07:43 bin -> usr/bin
drwxr-xr-x  2 20000 20000 4096 Apr 15  2020 boot
drwxr-xr-x  3 20000 20000 4096 Oct 16 19:26 dev
drwxr-xr-x 61 20000 20000 4096 Oct 16 19:26 etc
drwxr-xr-x  3 20000 20000 4096 Sep 24 07:45 home
lrwxrwxrwx  1 20000 20000    7 Sep 24 07:43 lib -> usr/lib
lrwxrwxrwx  1 20000 20000    9 Sep 24 07:43 lib32 -> usr/lib32
lrwxrwxrwx  1 20000 20000    9 Sep 24 07:43 lib64 -> usr/lib64
lrwxrwxrwx  1 20000 20000   10 Sep 24 07:43 libx32 -> usr/libx32
drwxr-xr-x  2 20000 20000 4096 Sep 24 07:43 media
drwxr-xr-x  2 20000 20000 4096 Sep 24 07:43 mnt
drwxr-xr-x  2 20000 20000 4096 Sep 24 07:43 opt
drwxr-xr-x  2 20000 20000 4096 Apr 15  2020 proc
drwx------  2 20000 20000 4096 Sep 24 07:43 root
drwxr-xr-x  2 20000 20000 4096 Sep 24 07:45 run
lrwxrwxrwx  1 20000 20000    8 Sep 24 07:43 sbin -> usr/sbin
drwxr-xr-x  2 20000 20000 4096 Sep 24 07:43 srv
drwxr-xr-x  2 20000 20000 4096 Apr 15  2020 sys
drwxrwxrwt  2 20000 20000 4096 Sep 24 07:44 tmp
drwxr-xr-x 13 20000 20000 4096 Sep 24 07:43 usr
drwxr-xr-x 12 20000 20000 4096 Sep 24 07:44 var
root@...vm:~# /mount-idmapped --map-mount b:20000:10000:100000 /var/lib/lxc/f2/rootfs/ /mnt
root@...vm:~# ls -al /mnt
total 68
drwxr-xr-x 17 10000 10000 4096 Sep 24 07:48 .
drwxr-xr-x 34 root  root  4096 Oct 28 22:24 ..
lrwxrwxrwx  1 10000 10000    7 Sep 24 07:43 bin -> usr/bin
drwxr-xr-x  2 10000 10000 4096 Apr 15  2020 boot
drwxr-xr-x  3 10000 10000 4096 Oct 16 19:26 dev
drwxr-xr-x 61 10000 10000 4096 Oct 16 19:26 etc
drwxr-xr-x  3 10000 10000 4096 Sep 24 07:45 home
lrwxrwxrwx  1 10000 10000    7 Sep 24 07:43 lib -> usr/lib
lrwxrwxrwx  1 10000 10000    9 Sep 24 07:43 lib32 -> usr/lib32
lrwxrwxrwx  1 10000 10000    9 Sep 24 07:43 lib64 -> usr/lib64
lrwxrwxrwx  1 10000 10000   10 Sep 24 07:43 libx32 -> usr/libx32
drwxr-xr-x  2 10000 10000 4096 Sep 24 07:43 media
drwxr-xr-x  2 10000 10000 4096 Sep 24 07:43 mnt
drwxr-xr-x  2 10000 10000 4096 Sep 24 07:43 opt
drwxr-xr-x  2 10000 10000 4096 Apr 15  2020 proc
drwx------  2 10000 10000 4096 Sep 24 07:43 root
drwxr-xr-x  2 10000 10000 4096 Sep 24 07:45 run
lrwxrwxrwx  1 10000 10000    8 Sep 24 07:43 sbin -> usr/sbin
drwxr-xr-x  2 10000 10000 4096 Sep 24 07:43 srv
drwxr-xr-x  2 10000 10000 4096 Apr 15  2020 sys
drwxrwxrwt  2 10000 10000 4096 Sep 24 07:44 tmp
drwxr-xr-x 13 10000 10000 4096 Sep 24 07:43 usr
drwxr-xr-x 12 10000 10000 4096 Sep 24 07:44 var
root@...vm:~# lxc-start f2 # uses /mnt as rootfs
root@...vm:~# lxc-attach f2 -- cat /proc/1/uid_map
         0      10000      10000
root@...vm:~# lxc-attach f2 -- cat /proc/1/gid_map
         0      10000      10000
root@...vm:~# lxc-attach f2 -- ls -al /
total 52
drwxr-xr-x  17 root   root    4096 Sep 24 07:48 .
drwxr-xr-x  17 root   root    4096 Sep 24 07:48 ..
lrwxrwxrwx   1 root   root       7 Sep 24 07:43 bin -> usr/bin
drwxr-xr-x   2 root   root    4096 Apr 15  2020 boot
drwxr-xr-x   5 root   root     500 Oct 28 23:39 dev
drwxr-xr-x  61 root   root    4096 Oct 28 23:39 etc
drwxr-xr-x   3 root   root    4096 Sep 24 07:45 home
lrwxrwxrwx   1 root   root       7 Sep 24 07:43 lib -> usr/lib
lrwxrwxrwx   1 root   root       9 Sep 24 07:43 lib32 -> usr/lib32
lrwxrwxrwx   1 root   root       9 Sep 24 07:43 lib64 -> usr/lib64
lrwxrwxrwx   1 root   root      10 Sep 24 07:43 libx32 -> usr/libx32
drwxr-xr-x   2 root   root    4096 Sep 24 07:43 media
drwxr-xr-x   2 root   root    4096 Sep 24 07:43 mnt
drwxr-xr-x   2 root   root    4096 Sep 24 07:43 opt
dr-xr-xr-x 232 nobody nogroup    0 Oct 28 23:39 proc
drwx------   2 root   root    4096 Oct 28 23:41 root
drwxr-xr-x  12 root   root     360 Oct 28 23:39 run
lrwxrwxrwx   1 root   root       8 Sep 24 07:43 sbin -> usr/sbin
drwxr-xr-x   2 root   root    4096 Sep 24 07:43 srv
dr-xr-xr-x  13 nobody nogroup    0 Oct 28 23:39 sys
drwxrwxrwt  11 root   root    4096 Oct 28 23:40 tmp
drwxr-xr-x  13 root   root    4096 Sep 24 07:43 usr
drwxr-xr-x  12 root   root    4096 Sep 24 07:44 var
root@...vm:~# lxc-attach f2 -- ls -al /my-file
-rw-r--r-- 1 root root 0 Oct 28 23:43 /my-file
root@...vm:~# ls -al /var/lib/lxc/f2/rootfs/my-file
-rw-r--r-- 1 20000 20000 0 Oct 28 23:43 /var/lib/lxc/f2/rootfs/my-file

I'd like to say thanks to:
Al for pointing me into the direction to avoid inode alias issues during
lookup. David for various discussions around this. Christoph for porting
xfs, providing good reviews and for being involved in the original idea.
Tycho for helping with this series and on future patches to convert
filesystems. Alban Crequy and the Kinvolk peeps located just a few
streets away from me in Berlin for providing use-case discussions and
writing patches for containerd. Stéphane for his invaluable input on
many things and level head and enabling me to work on this. Amir for
explaining and discussing aspects of overlayfs with me. I'd like to
especially thank Seth Forshee. He provided a lot of good analysis,
suggestions, and participated in short-notice discussions in both chat
and video for some nitty-gritty technical details.

This series can be found and pulled from the three usual locations:
https://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git/log/?h=idmapped_mounts
https://github.com/brauner/linux/tree/idmapped_mounts
https://gitlab.com/brauner/linux/-/commits/idmapped_mounts

/* v5 */
- Adress Christoph's feedback.
- Use v5.11-rc3 as new base.
- Add Christoph's xfs port.

/* v4 */
- Split out several preparatory patches from the initial mount_setattr
  patch as requested by Christoph.
- Add new tests for file/directory creation in directories with the
  setgid bit set. Specifically, verify that the setgid bit is correctly
  ignored when creating a file with the setgid bit and the parent
  directory's i_gid isn't in_group_p() and the caller isn't
  capable_wrt_inode_uidgid() over the parent directory's inode when
  inode_init_owner() is called.
  Conversely, verify that the setgid bit is set when creating a file
  with the setgid bit and the parent's i_gid is either in_group_p() or
  the caller is capable_wrt_inode_uidgid() over the parent directory's
  inode. In additiona, verify that the setgid bit is always inherited
  when creating directories.
  Test all of this on regular mounts, idmapped mounts, and on idmapped
  mounts in user namespaces.
- Add new tests to verify that the i_gid of newly created files or
  directories is correctly set to the parent directory's i_gid when the
  parent directory has the setgid bit set.
- Use "mnt_userns" as the de facto name for a vfsmount's user namespace
  everywhere as suggested by Serge.
- Reuse existing propagation flags instead of introducing new ones as
  suggested by Christoph. (This is in line with Linus request to not
  introduce too many new flags as evidenced by prior discussions on
  other patchsets such as openat2().)
- Add first set of Acked-bys from Serge and Reviewed-bys from Christoph.
- Fix commit messages to reflect the fact that we modify existing
  vfs helpers but do not introduce new ones like we did in the first
  version. Some commit messages still implied we were adding new
  helpers.
- Reformat all commit messages to adhere to 73 char length limit and
  wrap all lines in commits at 80 chars whenever this doesn't hinder
  legibility.
- Simplify various codepaths with Christoph's suggestions.

/* v3 */
- The major change is the port of the test-suite from the
  kernel-internal selftests framework to xfstests as requested by
  Darrick and Christoph. The test-suite for xfstests is patch 38 in this
  series. It has been kept as part of this series even though it belongs
  to xfstests so it's easier to see what is tested and to keep it
  in-sync.
- Note, the test-suite now has been extended to cover io_uring and
  idmapped mounts. The IORING_REGISTER_PERSONALITY feature allows to
  register the caller's credentials with io_uring and returns an id
  associated with these credentials. This is useful for applications
  that wish to share a ring between separate users/processes. Callers
  can pass in the credential id in the sqe personality field. If set,
  that particular sqe will be issued with these credentials.
  The test-suite now tests that the openat* operations with different
  registered credentials work correctly and safely on regular mounts, on
  regular mounts inside user namespaces, on idmapped mounts, and on
  idmapped mounts inside user namespaces.

/* v2 */
- The major change is the rework requested by Christoph and others to
  adapt all relevant helpers and inode_operations methods to account for
  idmapped mounts instead of introducing new helpers and methods
  specific to idmapped mounts like we did before. We've also moved the
  overlayfs conversion to handle idmapped mounts into a separate
  patchset that will be sent out separately after the core changes
  landed. The converted filesytems in this series include fat and ext4.
  As per Christoph's request the vfs-wide config option to disable
  idmapped mounts has been removed. Instead the filesystems can decide
  whether or not they want to allow idmap mounts through a config
  option. These config options default to off. Having a config option
  allows us to gain some confidence in the patchset over multiple kernel
  releases.
- This version introduces a large test-suite to test current vfs
  behavior and idmapped mounts behavior. This test-suite is intended to
  grow over time.
- While while working on adapting this patchset to the requested
  changes, the runC and containerd crowd was nice enough to adapt
  containerd to this patchset to make use of idmapped mounts in one of
  the most widely used container runtimes:
  https://github.com/containerd/containerd/pull/4734

The solution proposed here has it's origins in multiple discussions
during Linux Plumbers 2017 during and after the end of the containers
microconference.
To the best of my knowledge this involved Aleksa, Stéphane, Eric, David,
James, and myself.The original idea or a variant thereof has been
discussed, again to the best of my knowledge, after a Linux conference
in St. Petersburg in Russia in 2017 between Christoph, Tycho, and
myself.
We've taken the time to implement a working version of this solution
over the last weeks to the best of my abilities. Tycho has signed up
for this sligthly crazy endeavour as well and he has helped with the
conversion of the xattr codepaths and will be involved with others in
converting additional filesystems.

Thanks!
Christian

Christian Brauner (39):
  namespace: take lock_mount_hash() directly when changing flags
  mount: make {lock,unlock}_mount_hash() static
  namespace: only take read lock in do_reconfigure_mnt()
  fs: split out functions to hold writers
  fs: add attr_flags_to_mnt_flags helper
  fs: add mount_setattr()
  tests: add mount_setattr() selftests
  fs: add id translation helpers
  mount: attach mappings to mounts
  capability: handle idmapped mounts
  namei: make permission helpers idmapped mount aware
  inode: make init and permission helpers idmapped mount aware
  attr: handle idmapped mounts
  acl: handle idmapped mounts
  fs: add file_user_ns() helper
  commoncap: handle idmapped mounts
  stat: handle idmapped mounts
  namei: handle idmapped mounts in may_*() helpers
  namei: introduce struct renamedata
  namei: prepare for idmapped mounts
  open: handle idmapped mounts in do_truncate()
  open: handle idmapped mounts
  af_unix: handle idmapped mounts
  utimes: handle idmapped mounts
  fcntl: handle idmapped mounts
  notify: handle idmapped mounts
  init: handle idmapped mounts
  ioctl: handle idmapped mounts
  would_dump: handle idmapped mounts
  exec: handle idmapped mounts
  fs: make helpers idmap mount aware
  apparmor: handle idmapped mounts
  ima: handle idmapped mounts
  fat: handle idmapped mounts
  ext4: support idmapped mounts
  ecryptfs: do not mount on top of idmapped mounts
  overlayfs: do not mount on top of idmapped mounts
  fs: introduce MOUNT_ATTR_IDMAP
  tests: extend mount_setattr tests

Christoph Hellwig (1):
  xfs: support idmapped mounts

Tycho Andersen (1):
  xattr: handle idmapped mounts

 Documentation/filesystems/locking.rst         |    6 +-
 Documentation/filesystems/porting.rst         |    2 +
 Documentation/filesystems/vfs.rst             |   19 +-
 arch/alpha/kernel/syscalls/syscall.tbl        |    1 +
 arch/arm/tools/syscall.tbl                    |    1 +
 arch/arm64/include/asm/unistd32.h             |    2 +
 arch/ia64/kernel/syscalls/syscall.tbl         |    1 +
 arch/m68k/kernel/syscalls/syscall.tbl         |    1 +
 arch/microblaze/kernel/syscalls/syscall.tbl   |    1 +
 arch/mips/kernel/syscalls/syscall_n32.tbl     |    1 +
 arch/mips/kernel/syscalls/syscall_n64.tbl     |    1 +
 arch/mips/kernel/syscalls/syscall_o32.tbl     |    1 +
 arch/parisc/kernel/syscalls/syscall.tbl       |    1 +
 arch/powerpc/kernel/syscalls/syscall.tbl      |    1 +
 arch/powerpc/platforms/cell/spufs/inode.c     |    5 +-
 arch/s390/kernel/syscalls/syscall.tbl         |    1 +
 arch/sh/kernel/syscalls/syscall.tbl           |    1 +
 arch/sparc/kernel/syscalls/syscall.tbl        |    1 +
 arch/x86/entry/syscalls/syscall_32.tbl        |    1 +
 arch/x86/entry/syscalls/syscall_64.tbl        |    1 +
 arch/xtensa/kernel/syscalls/syscall.tbl       |    1 +
 drivers/android/binderfs.c                    |    6 +-
 drivers/base/devtmpfs.c                       |   12 +-
 fs/9p/acl.c                                   |    8 +-
 fs/9p/v9fs.h                                  |    3 +-
 fs/9p/v9fs_vfs.h                              |    2 +-
 fs/9p/vfs_inode.c                             |   36 +-
 fs/9p/vfs_inode_dotl.c                        |   39 +-
 fs/9p/xattr.c                                 |    1 +
 fs/adfs/adfs.h                                |    3 +-
 fs/adfs/inode.c                               |    5 +-
 fs/affs/affs.h                                |   10 +-
 fs/affs/inode.c                               |    7 +-
 fs/affs/namei.c                               |   15 +-
 fs/afs/dir.c                                  |   34 +-
 fs/afs/inode.c                                |    9 +-
 fs/afs/internal.h                             |    7 +-
 fs/afs/security.c                             |    2 +-
 fs/afs/xattr.c                                |    2 +
 fs/attr.c                                     |  124 +-
 fs/autofs/root.c                              |   13 +-
 fs/bad_inode.c                                |   36 +-
 fs/bfs/dir.c                                  |   12 +-
 fs/btrfs/acl.c                                |    5 +-
 fs/btrfs/ctree.h                              |    3 +-
 fs/btrfs/inode.c                              |   45 +-
 fs/btrfs/ioctl.c                              |   25 +-
 fs/btrfs/tests/btrfs-tests.c                  |    2 +-
 fs/btrfs/xattr.c                              |    2 +
 fs/cachefiles/interface.c                     |    4 +-
 fs/cachefiles/namei.c                         |   19 +-
 fs/cachefiles/xattr.c                         |   16 +-
 fs/ceph/acl.c                                 |    5 +-
 fs/ceph/dir.c                                 |   23 +-
 fs/ceph/inode.c                               |   17 +-
 fs/ceph/super.h                               |   12 +-
 fs/ceph/xattr.c                               |    1 +
 fs/cifs/cifsfs.c                              |    4 +-
 fs/cifs/cifsfs.h                              |   21 +-
 fs/cifs/dir.c                                 |    8 +-
 fs/cifs/inode.c                               |   26 +-
 fs/cifs/link.c                                |    3 +-
 fs/cifs/xattr.c                               |    1 +
 fs/coda/coda_linux.h                          |    6 +-
 fs/coda/dir.c                                 |   17 +-
 fs/coda/inode.c                               |    9 +-
 fs/coda/pioctl.c                              |    6 +-
 fs/configfs/configfs_internal.h               |    7 +-
 fs/configfs/dir.c                             |    3 +-
 fs/configfs/inode.c                           |    5 +-
 fs/configfs/symlink.c                         |    5 +-
 fs/coredump.c                                 |   14 +-
 fs/crypto/policy.c                            |    2 +-
 fs/debugfs/inode.c                            |    9 +-
 fs/ecryptfs/crypto.c                          |    4 +-
 fs/ecryptfs/inode.c                           |   80 +-
 fs/ecryptfs/main.c                            |    6 +
 fs/ecryptfs/mmap.c                            |    4 +-
 fs/efivarfs/file.c                            |    2 +-
 fs/efivarfs/inode.c                           |    4 +-
 fs/erofs/inode.c                              |    7 +-
 fs/erofs/internal.h                           |    5 +-
 fs/exec.c                                     |   12 +-
 fs/exfat/exfat_fs.h                           |    8 +-
 fs/exfat/file.c                               |   14 +-
 fs/exfat/namei.c                              |   14 +-
 fs/ext2/acl.c                                 |    5 +-
 fs/ext2/acl.h                                 |    3 +-
 fs/ext2/ext2.h                                |    5 +-
 fs/ext2/ialloc.c                              |    2 +-
 fs/ext2/inode.c                               |   15 +-
 fs/ext2/ioctl.c                               |    6 +-
 fs/ext2/namei.c                               |   22 +-
 fs/ext2/xattr_security.c                      |    1 +
 fs/ext2/xattr_trusted.c                       |    1 +
 fs/ext2/xattr_user.c                          |    1 +
 fs/ext4/acl.c                                 |    5 +-
 fs/ext4/acl.h                                 |    3 +-
 fs/ext4/ext4.h                                |   21 +-
 fs/ext4/ialloc.c                              |    7 +-
 fs/ext4/inode.c                               |   21 +-
 fs/ext4/ioctl.c                               |   19 +-
 fs/ext4/namei.c                               |   49 +-
 fs/ext4/super.c                               |    2 +-
 fs/ext4/xattr_hurd.c                          |    1 +
 fs/ext4/xattr_security.c                      |    1 +
 fs/ext4/xattr_trusted.c                       |    1 +
 fs/ext4/xattr_user.c                          |    1 +
 fs/f2fs/acl.c                                 |    5 +-
 fs/f2fs/acl.h                                 |    3 +-
 fs/f2fs/f2fs.h                                |    7 +-
 fs/f2fs/file.c                                |   35 +-
 fs/f2fs/namei.c                               |   23 +-
 fs/f2fs/xattr.c                               |    4 +-
 fs/fat/fat.h                                  |    6 +-
 fs/fat/file.c                                 |   24 +-
 fs/fat/namei_msdos.c                          |   12 +-
 fs/fat/namei_vfat.c                           |   15 +-
 fs/fcntl.c                                    |    3 +-
 fs/fuse/acl.c                                 |    3 +-
 fs/fuse/dir.c                                 |   45 +-
 fs/fuse/fuse_i.h                              |    4 +-
 fs/fuse/xattr.c                               |    2 +
 fs/gfs2/acl.c                                 |    5 +-
 fs/gfs2/acl.h                                 |    3 +-
 fs/gfs2/file.c                                |    4 +-
 fs/gfs2/inode.c                               |   59 +-
 fs/gfs2/inode.h                               |    3 +-
 fs/gfs2/xattr.c                               |    1 +
 fs/hfs/attr.c                                 |    1 +
 fs/hfs/dir.c                                  |   13 +-
 fs/hfs/hfs_fs.h                               |    2 +-
 fs/hfs/inode.c                                |    7 +-
 fs/hfsplus/dir.c                              |   25 +-
 fs/hfsplus/hfsplus_fs.h                       |    5 +-
 fs/hfsplus/inode.c                            |   16 +-
 fs/hfsplus/ioctl.c                            |    2 +-
 fs/hfsplus/xattr.c                            |    1 +
 fs/hfsplus/xattr_security.c                   |    1 +
 fs/hfsplus/xattr_trusted.c                    |    1 +
 fs/hfsplus/xattr_user.c                       |    1 +
 fs/hostfs/hostfs_kern.c                       |   29 +-
 fs/hpfs/hpfs_fn.h                             |    2 +-
 fs/hpfs/inode.c                               |    7 +-
 fs/hpfs/namei.c                               |   20 +-
 fs/hugetlbfs/inode.c                          |   31 +-
 fs/init.c                                     |   27 +-
 fs/inode.c                                    |   50 +-
 fs/internal.h                                 |    2 +-
 fs/jffs2/acl.c                                |    5 +-
 fs/jffs2/acl.h                                |    3 +-
 fs/jffs2/dir.c                                |   32 +-
 fs/jffs2/fs.c                                 |    7 +-
 fs/jffs2/os-linux.h                           |    2 +-
 fs/jffs2/security.c                           |    1 +
 fs/jffs2/xattr_trusted.c                      |    1 +
 fs/jffs2/xattr_user.c                         |    1 +
 fs/jfs/acl.c                                  |    5 +-
 fs/jfs/file.c                                 |    9 +-
 fs/jfs/ioctl.c                                |    2 +-
 fs/jfs/jfs_acl.h                              |    3 +-
 fs/jfs/jfs_inode.c                            |    2 +-
 fs/jfs/jfs_inode.h                            |    2 +-
 fs/jfs/namei.c                                |   21 +-
 fs/jfs/xattr.c                                |    2 +
 fs/kernfs/dir.c                               |    7 +-
 fs/kernfs/inode.c                             |   19 +-
 fs/kernfs/kernfs-internal.h                   |    9 +-
 fs/libfs.c                                    |   28 +-
 fs/minix/bitmap.c                             |    2 +-
 fs/minix/file.c                               |    7 +-
 fs/minix/inode.c                              |    6 +-
 fs/minix/minix.h                              |    3 +-
 fs/minix/namei.c                              |   24 +-
 fs/mount.h                                    |   10 -
 fs/namei.c                                    |  513 ++++--
 fs/namespace.c                                |  484 +++++-
 fs/nfs/dir.c                                  |   25 +-
 fs/nfs/inode.c                                |    9 +-
 fs/nfs/internal.h                             |   10 +-
 fs/nfs/namespace.c                            |   14 +-
 fs/nfs/nfs3_fs.h                              |    3 +-
 fs/nfs/nfs3acl.c                              |    3 +-
 fs/nfs/nfs4proc.c                             |    3 +
 fs/nfsd/nfs2acl.c                             |    4 +-
 fs/nfsd/nfs3acl.c                             |    4 +-
 fs/nfsd/nfs4acl.c                             |    4 +-
 fs/nfsd/nfs4recover.c                         |    6 +-
 fs/nfsd/nfsfh.c                               |    2 +-
 fs/nfsd/nfsproc.c                             |    2 +-
 fs/nfsd/vfs.c                                 |   47 +-
 fs/nilfs2/inode.c                             |   13 +-
 fs/nilfs2/ioctl.c                             |    2 +-
 fs/nilfs2/namei.c                             |   19 +-
 fs/nilfs2/nilfs.h                             |    4 +-
 fs/notify/fanotify/fanotify_user.c            |    2 +-
 fs/notify/inotify/inotify_user.c              |    3 +-
 fs/ntfs/inode.c                               |    6 +-
 fs/ntfs/inode.h                               |    3 +-
 fs/ocfs2/acl.c                                |    5 +-
 fs/ocfs2/acl.h                                |    3 +-
 fs/ocfs2/dlmfs/dlmfs.c                        |   17 +-
 fs/ocfs2/file.c                               |   17 +-
 fs/ocfs2/file.h                               |   11 +-
 fs/ocfs2/ioctl.c                              |    2 +-
 fs/ocfs2/namei.c                              |   21 +-
 fs/ocfs2/refcounttree.c                       |    4 +-
 fs/ocfs2/xattr.c                              |    3 +
 fs/omfs/dir.c                                 |   13 +-
 fs/omfs/file.c                                |    7 +-
 fs/omfs/inode.c                               |    2 +-
 fs/open.c                                     |   50 +-
 fs/orangefs/acl.c                             |    5 +-
 fs/orangefs/inode.c                           |   20 +-
 fs/orangefs/namei.c                           |   12 +-
 fs/orangefs/orangefs-kernel.h                 |   13 +-
 fs/orangefs/xattr.c                           |    1 +
 fs/overlayfs/copy_up.c                        |   20 +-
 fs/overlayfs/dir.c                            |   31 +-
 fs/overlayfs/file.c                           |    6 +-
 fs/overlayfs/inode.c                          |   26 +-
 fs/overlayfs/overlayfs.h                      |   44 +-
 fs/overlayfs/super.c                          |   19 +-
 fs/overlayfs/util.c                           |    4 +-
 fs/posix_acl.c                                |  101 +-
 fs/proc/base.c                                |   28 +-
 fs/proc/fd.c                                  |    5 +-
 fs/proc/fd.h                                  |    3 +-
 fs/proc/generic.c                             |   12 +-
 fs/proc/internal.h                            |    5 +-
 fs/proc/proc_net.c                            |    5 +-
 fs/proc/proc_sysctl.c                         |   15 +-
 fs/proc/root.c                                |    5 +-
 fs/proc_namespace.c                           |    3 +
 fs/ramfs/file-nommu.c                         |    9 +-
 fs/ramfs/inode.c                              |   18 +-
 fs/reiserfs/acl.h                             |    3 +-
 fs/reiserfs/inode.c                           |    7 +-
 fs/reiserfs/ioctl.c                           |    4 +-
 fs/reiserfs/namei.c                           |   21 +-
 fs/reiserfs/reiserfs.h                        |    3 +-
 fs/reiserfs/xattr.c                           |   12 +-
 fs/reiserfs/xattr.h                           |    3 +-
 fs/reiserfs/xattr_acl.c                       |    7 +-
 fs/reiserfs/xattr_security.c                  |    3 +-
 fs/reiserfs/xattr_trusted.c                   |    3 +-
 fs/reiserfs/xattr_user.c                      |    3 +-
 fs/remap_range.c                              |    7 +-
 fs/stat.c                                     |   26 +-
 fs/sysv/file.c                                |    7 +-
 fs/sysv/ialloc.c                              |    2 +-
 fs/sysv/itree.c                               |    6 +-
 fs/sysv/namei.c                               |   21 +-
 fs/sysv/sysv.h                                |    3 +-
 fs/tracefs/inode.c                            |    4 +-
 fs/ubifs/dir.c                                |   30 +-
 fs/ubifs/file.c                               |    5 +-
 fs/ubifs/ioctl.c                              |    2 +-
 fs/ubifs/ubifs.h                              |    5 +-
 fs/ubifs/xattr.c                              |    1 +
 fs/udf/file.c                                 |    9 +-
 fs/udf/ialloc.c                               |    2 +-
 fs/udf/namei.c                                |   24 +-
 fs/udf/symlink.c                              |    7 +-
 fs/ufs/ialloc.c                               |    2 +-
 fs/ufs/inode.c                                |    7 +-
 fs/ufs/namei.c                                |   19 +-
 fs/ufs/ufs.h                                  |    3 +-
 fs/utimes.c                                   |    4 +-
 fs/vboxsf/dir.c                               |   12 +-
 fs/vboxsf/utils.c                             |    9 +-
 fs/vboxsf/vfsmod.h                            |    8 +-
 fs/verity/enable.c                            |    2 +-
 fs/xattr.c                                    |  136 +-
 fs/xfs/xfs_acl.c                              |    5 +-
 fs/xfs/xfs_acl.h                              |    3 +-
 fs/xfs/xfs_file.c                             |    4 +-
 fs/xfs/xfs_inode.c                            |   26 +-
 fs/xfs/xfs_inode.h                            |   16 +-
 fs/xfs/xfs_ioctl.c                            |   23 +-
 fs/xfs/xfs_iops.c                             |   98 +-
 fs/xfs/xfs_iops.h                             |    3 +-
 fs/xfs/xfs_qm.c                               |    3 +-
 fs/xfs/xfs_super.c                            |    2 +-
 fs/xfs/xfs_symlink.c                          |    5 +-
 fs/xfs/xfs_symlink.h                          |    5 +-
 fs/xfs/xfs_xattr.c                            |    3 +-
 fs/zonefs/super.c                             |    9 +-
 include/linux/capability.h                    |   15 +-
 include/linux/fs.h                            |  158 +-
 include/linux/ima.h                           |   17 +-
 include/linux/lsm_hook_defs.h                 |   15 +-
 include/linux/lsm_hooks.h                     |    1 +
 include/linux/mount.h                         |    7 +
 include/linux/nfs_fs.h                        |    7 +-
 include/linux/posix_acl.h                     |   15 +-
 include/linux/posix_acl_xattr.h               |   12 +-
 include/linux/security.h                      |   46 +-
 include/linux/syscalls.h                      |    4 +
 include/linux/xattr.h                         |   30 +-
 include/uapi/asm-generic/unistd.h             |    4 +-
 include/uapi/linux/mount.h                    |   17 +
 ipc/mqueue.c                                  |    8 +-
 kernel/auditsc.c                              |    5 +-
 kernel/bpf/inode.c                            |   13 +-
 kernel/capability.c                           |   14 +-
 kernel/cgroup/cgroup.c                        |    2 +-
 kernel/sys.c                                  |    2 +-
 mm/madvise.c                                  |    4 +-
 mm/memcontrol.c                               |    2 +-
 mm/mincore.c                                  |    4 +-
 mm/shmem.c                                    |   48 +-
 net/socket.c                                  |    6 +-
 net/unix/af_unix.c                            |    4 +-
 security/apparmor/apparmorfs.c                |    3 +-
 security/apparmor/domain.c                    |   13 +-
 security/apparmor/file.c                      |    5 +-
 security/apparmor/lsm.c                       |   12 +-
 security/commoncap.c                          |  109 +-
 security/integrity/evm/evm_crypto.c           |   11 +-
 security/integrity/evm/evm_main.c             |    4 +-
 security/integrity/evm/evm_secfs.c            |    2 +-
 security/integrity/ima/ima.h                  |   19 +-
 security/integrity/ima/ima_api.c              |   10 +-
 security/integrity/ima/ima_appraise.c         |   22 +-
 security/integrity/ima/ima_asymmetric_keys.c  |    2 +-
 security/integrity/ima/ima_main.c             |   31 +-
 security/integrity/ima/ima_policy.c           |   19 +-
 security/integrity/ima/ima_queue_keys.c       |    2 +-
 security/security.c                           |   25 +-
 security/selinux/hooks.c                      |   22 +-
 security/smack/smack_lsm.c                    |   18 +-
 tools/include/uapi/asm-generic/unistd.h       |    4 +-
 tools/testing/selftests/Makefile              |    1 +
 .../selftests/mount_setattr/.gitignore        |    1 +
 .../testing/selftests/mount_setattr/Makefile  |    7 +
 tools/testing/selftests/mount_setattr/config  |    1 +
 .../mount_setattr/mount_setattr_test.c        | 1424 +++++++++++++++++
 338 files changed, 4718 insertions(+), 1731 deletions(-)
 create mode 100644 tools/testing/selftests/mount_setattr/.gitignore
 create mode 100644 tools/testing/selftests/mount_setattr/Makefile
 create mode 100644 tools/testing/selftests/mount_setattr/config
 create mode 100644 tools/testing/selftests/mount_setattr/mount_setattr_test.c


base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837
-- 
2.30.0

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