On Wed, Mar 30, 2022 at 04:58:03PM -0400, Vivek Goyal wrote: > On Tue, Mar 29, 2022 at 12:35:07PM +0200, Christian Brauner wrote: > > From: "Christian Brauner (Microsoft)" <brauner@xxxxxxxxxx> > > > > Hey, > > > > This adds support for mounting overlay on top of idmapped layers. > > > > I have to start by saying a massive thank you to Amir! He did not just > > answer my constant overlay questions but also provided quite a few > > patches himself in this series in addition to reviews, comments and a > > lot of suggestions. Thank you! > > > > There have been a lot of requests to unblock this. For just a few select > > examples see [3], [4], and [5]. I've worked closely with various > > communities among them containerd, Kubernetes, Podman, LXD, runC, crun, > > and systemd (For the curious please see the various pull-request and > > issues below.) a lot of them already support idmapped mounts since they > > are enabled for btrfs, ext4, and xfs (and f2fs and fat fwiw). In > > additon, a few colleagues at Microsoft and from Red Hat work on a > > Kubernetes Enhancement Proposals (KEP) that also relies on overlayfs > > supporting idmapped layers, see [12]. > > > > Overlayfs on top of idmapped layers will be used in various ways: > > > > * Container managers use overlayfs to efficiently share layers between > > containers. However, this only works for privileged containers. > > Layers cannot be shared if both privileged and unprivileged containers > > are used. Layers can also not be shared if non-overlapping idmappings > > are used for unprivileged containers. Layers cannot be shared because > > of the conflicting ownership requirements between the containers. > > Hi Christian, > > Thank you for this work. This is awesome. Thanks for saying that! Appreciate it. > > Wanted to test it. I was wondering how to test it. Some simple > instructions will help. Of course. There are various ways: 1. Giuseppe has already put up support the containers/storage go library: https://github.com/containers/storage/pull/1180 and he's been running workloads with that branch. If you're familiar with that tooling you can just use that. 2. xfstests have - for a long time already - support for a generic idmapped mount testsuite. Alongside that testsuite I added the "mount-idmapped" binary which makes it easy to create idmapped mounts. You can compile it via xfstests: https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/tree/src/idmapped-mounts/mount-idmapped.c I've pushed detailed instructions to the test repo at https://gitlab.com/brauner/fs.idmapped.overlay.xfstests.output They are avaiable in the "manual.test.instructions" file. > > I am assuming I will need to be priviliged to be able to setup idmapped > mounts. And then overlay can be mounted on top of these layers (either Yes. > as a priviliged operation outside container or unprivileged overlayfs > inside container). Sorry, just trying to wrap my head around which Correct. > operations will require me to be priviliged (root in init_user_ns) > and which operations I can do unprivileged (as normal user). > > Thanks > Vivek > > > > > Both the KEP proposal (see [13]) and LXD (see [14]) use > > non-overlapping idmappings to increase isolation. > > > > All of these cases can be supported if overlayfs can be mounted on > > idmapped layers. The container runtime will create idmapped mounts for > > the layers supposed to be shared. Each container will be given > > idmapped mounts with the correct idmapping. Either by attaching a > > custom or its own user namespace depending on the use-case. Then an > > overlay mount can be mounted on top of the idmapped layers. The > > underlying idmapped mounts can then be unmounted and the mount table > > will be in a clean state. > > This approach has been tested an verified by Giuseppe and others. > > > > * Because of the inability to share layers preparing a layer causes a > > big runtime overhead as ownership needs to be recursively changed. > > This becomes increasingly costly with the bigger the layers are. > > Especially for a large rootfs it becomes prohibitively expensive. > > > > This recursive ownership change also causes a lot storage overhead. > > Without metacopy it can quickly become unmanagable. With metacopy it > > still wastes a lot of space and inodes. > > > > For both the KEP and container manager being able to use idmapped > > layer with overlayfs on top of it solves all these problems. > > > > * Container managers such as LXD do run full system containers. Such > > systems are managed like virtual machines and users run application > > containers inside. Since LXD uses an idmapped mounts for the rootfs of > > the container with the container's user namespace attached to the > > mount container runtimes cannot user overlayfs inside. > > > > Once overlayfs can be mounted on top of idmapped layers it will be > > possible for container runtimes to use overlayfs inside LXD > > containers. > > > > * The systemd-homed daemon and toolsuite is a new component of systemd > > to manage home areas in a portable way. systemd-homed makes use of > > idmapped mounts for the home areas. If the kernel and used file system > > support it the user's home area will be mounted as an idmapped mount > > when they log into their system. > > > > All files are internally owned by the "nobody" user (i.e. the user > > typically used for indicating "this ownership is not mapped"), and > > dynamically mapped to the {g,u}id used locally on the system via > > idmapped mounts. This makes migrating home areas between different > > systems trivial because recursively chown()ing file system trees is no > > longer necessary. This also means that it is impossible to store files > > as {g,u}id 0 on disk. > > > > Once overlayfs can be mounted on top of idmapped layers it will be > > possible for container runtimes to work better together with > > systemd-homed. > > > > * systemd provides various sandboxing features (see [11]) for services. > > These serve as hardening measures. In this context, idmapped mounts > > can be used to prevent services from creating files on disk as {g,u}id > > 0, making specific files inaccessible, or to prevent access to whole > > directories. Since such services may also make use of overlayfs for > > e.g. the ExtensionImages= option supporting overlayfs on top of > > idmapped layers would be another huge hardening win. > > > > * systemd provides the ability to use system extension images [15] for > > /usr and /opt (with a look to /etc in the future). Such system > > extension images contain files and directories similar in fashion to > > a regular OS system tree. When one or more system extension images are > > activated, their /usr/ and /opt/ hierarchies are combined via > > overlay with the same hierarchies of the host OS, and the host /usr/ > > and /opt/ overmounted with it ("merging"). These images are read-only. > > > > This feature is available to unprivileged container and sandboxed > > services as well. Idmapped layers are used here to avoid runtime and > > storage overhead from recursively changing ownership and ultimately an > > overlay mount is supposed to be created on top of it. > > > > Giuseppe provided testing for runC/crun/Podman and he put up a pull > > request to support overlayfs on top of idmapped layers at [16]. That > > already covers a lot of users. Other tools have put up pull requests as > > well and they are linked below. > > > > The patchset has been extensively tested for about 2 weeks with > > xfstests. The tests and results are explained in the following > > paragraphs. > > > > In order to test overlayfs with idmapped mounts a simple patch to > > xfstests has been added which is part of this series. The patchset > > simply allows for each test in the xfstests suite to be run on top of > > idmapped mounts. That is in addition to the generic idmapped mount tests > > that have existed and are already run for a long time. > > > > Since idmapped mounts can be created on top of btrfs, ext4, and xfs and > > these are the most relevant filesystems for users they were taken into > > the test matrix. > > > > Amir ensured that the test matrix also includes metacopy. So all tests > > are run once with metacopy=on and once with metacopy=off. > > > > Additionally, the unionmount tesuite that Amir maintains was run as part > > of xfstests. This brings testing for multi layer overlay and a few > > rarely used overlayfs use-cases. > > > > And last, xfstests were run with and without idmapped mounts. > > > > Since the patch series is based on Linux 5.17 the 5.17 kernel was chosen > > as a baseline kernel. The baseline kernel is pure 5.17 upstream without > > any of the patches in this series. The baseline kernel was used to run > > all xfstests with the same parameters minus the idmapped mount part of > > the test matrix. This ensured that regressions would be immediately > > noticeable. > > > > So the full test matrix is: > > > > ext4 x metacopy=off x -idmapped mounts > > ext4 x metacopy=on x -idmapped mounts > > ext4 x metacopy=off x +idmapped mounts > > ext4 x metacopy=on x +idmapped mounts > > > > xfs x metacopy=off x -idmapped mounts > > xfs x metacopy=on x -idmapped mounts > > xfs x metacopy=off x +idmapped mounts > > xfs x metacopy=on x +idmapped mounts > > > > btrfs x metacopy=off x -idmapped mounts > > btrfs x metacopy=on x -idmapped mounts > > btrfs x metacopy=off x +idmapped mounts > > btrfs x metacopy=on x +idmapped mounts > > > > The test runs were started with: > > > > sudo ./check -overlay > > > > so they encompass all xfstests apart from those that needed to be > > excluded because they triggered known issues (One such example is > > generic/530 which causes an xfs corruption that is currently under > > discussion for a fix upstream.). > > > > A single testrun with over 750 tests takes a bonkers long time given > > that I run them in a beefy VM on top of an ssd and not on bare metal. > > > > The successes and failures are identical for the whole test matrix with > > and without idmapped mounts. The tests and failures are also identical > > compared to the baseline kernel. All in all this should provide a good > > amount of convidence. The full test output can be found in the following > > repo: https://gitlab.com/brauner/fs.idmapped.overlay.xfstests.output > > > > In order to create an idmapped mount the mount_setattr() system call > > (see [17]) can be used together with the MOUNT_ATTR_IDMAP flag to attach > > a userns fd to a detached mount created with open_tree()'s > > OPEN_TREE_CLONE flag. The only effect is that the idmapping of the > > userns becomes the idmapping of the relevant. The links below should > > serve to illustrate how widely they are already used. > > > > For people who would like to test I've created a tag fs.idmapped.overlay.v1 > > which can be fetched: > > > > git fetch git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git fs.idmapped.overlay.v1 > > > > the same goes for xfstests: > > > > git fetch git://git.kernel.org/pub/scm/linux/kernel/git/brauner/xfstests-dev.git fs.idmapped.overlay.v1 > > > > Thanks! > > Christian > > > > [1]: OCI runtime-spec extension for idmapped mounts > > https://github.com/opencontainers/runtime-spec/pull/1143 > > > > [2]: Support for idmapped mounts for shared volumes > > https://github.com/opencontainers/runc/pull/3429 > > > > [3]: containerd support for idmapped mounts with focus on overlayfs > > https://github.com/containerd/containerd/pull/5890 > > > > [4]: runC support for idmapped mounts with focus on overlayfs > > https://github.com/opencontainers/runc/issues/2821 > > > > [5]: Podman support for idmapped mounts with focus on overlayfs > > https://github.com/containers/podman/issues/10374 > > > > [6]: systemd-nspawn support for idmapped mounts > > https://github.com/systemd/systemd/pull/19438 > > > > [7]: systemd-homed support for idmapped mounts > > https://github.com/systemd/systemd/pull/21136 > > > > [8]: LXD support for idmapped mounts > > https://github.com/lxc/lxd/pull/8778 > > > > [9]: LXC support for idmapped mounts > > https://github.com/lxc/lxc/pull/3709 > > > > [10]: crun support for idmapped mounts > > https://github.com/containers/crun/pull/874 > > > > [11]: https://www.freedesktop.org/software/systemd/man/systemd.exec.html#Sandboxing > > > > [12]: https://github.com/kubernetes/enhancements/pull/3065 > > > > [13]: https://github.com/kubernetes/enhancements/pull/3065/files#diff-a9ca9fbce1538447b92f03125ca2b8474e2d875071f1172d2afa0b1e8cadeabaR118 > > > > [14]: https://github.com/lxc/lxd/blob/master/doc/instances.md > > (The relevant entry can be found by looking for the > > "security.idmap.isolated" key.) > > > > [15]: https://www.freedesktop.org/software/systemd/man/systemd-sysext.html > > > > [16]: https://github.com/containers/storage/pull/1180 > > > > [17]: https://man7.org/linux/man-pages/man2/mount_setattr.2.html > > > > Amir Goldstein (3): > > ovl: use wrappers to all vfs_*xattr() calls > > ovl: pass layer mnt to ovl_open_realfile() > > ovl: store lower path in ovl_inode > > > > Christian Brauner (15): > > fs: add two trivial lookup helpers > > exportfs: support idmapped mounts > > ovl: pass ofs to creation operations > > ovl: handle idmappings in creation operations > > ovl: pass ofs to setattr operations > > ovl: use ovl_do_notify_change() wrapper > > ovl: use ovl_lookup_upper() wrapper > > ovl: use ovl_path_getxattr() wrapper > > ovl: handle idmappings for layer fileattrs > > ovl: handle idmappings for layer lookup > > ovl: use ovl_copy_{real,upper}attr() wrappers > > ovl: handle idmappings in ovl_permission() > > ovl: handle idmappings in layer open helpers > > ovl: handle idmappings in ovl_xattr_{g,s}et() > > ovl: support idmapped layers > > > > fs/exportfs/expfs.c | 5 +- > > fs/namei.c | 52 +++++++-- > > fs/overlayfs/copy_up.c | 97 +++++++++------- > > fs/overlayfs/dir.c | 133 +++++++++++----------- > > fs/overlayfs/export.c | 3 +- > > fs/overlayfs/file.c | 44 ++++---- > > fs/overlayfs/inode.c | 63 +++++++---- > > fs/overlayfs/namei.c | 49 ++++++--- > > fs/overlayfs/overlayfs.h | 231 ++++++++++++++++++++++++++++----------- > > fs/overlayfs/ovl_entry.h | 7 +- > > fs/overlayfs/readdir.c | 48 ++++---- > > fs/overlayfs/super.c | 57 +++++----- > > fs/overlayfs/util.c | 142 +++++++++++++++++++----- > > include/linux/namei.h | 2 + > > 14 files changed, 607 insertions(+), 326 deletions(-) > > > > > > base-commit: f443e374ae131c168a065ea1748feac6b2e76613 > > -- > > 2.32.0 > > >
