The kernel documentation added for the new helpers had a few tiny
ordering issues. Fix them.
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
The old non-type safe helpers will soon be removed.
Cc: Seth Forshee <sforshee@digitalocean.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
INVALID_VFS{U,G}ID represent ids which have no mapping in the target
mnt_usersns. This can happen for a couple of different reasons -- the
source id might be valid but has no mapping in mnt_userns, or the source
id might have been invalid (either due to a failed mapping or because it
was set to invalid to indicate it is uninitialized).
This means that two arbitrary vfs{u,g}ids which are both invalid could
represent two different underlying ids, or they could represent a failed
mapping and an uninitialized value. In these situation the vfs{u,g}id
equality functions evaluate these ids as equal, and care must be taken
when comparing ids to avoid problems. It would be less error prone to
always evaluate two invalid ids as not equal to each other, and to check
explicitly for vfs{u,g}id validity when that is needed.
Change all vfs{u,g}id equality functions to return false when both ids
are invalid. Functions for checking whether an id is valid exist and are
already being used by code which needs to check this.
Link: https://lore.kernel.org/linux-fsdevel/YrIMZirGoE0VIO45@do-x1extreme
Signed-off-by: Seth Forshee <sforshee@digitalocean.com>
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Add ia_vfs{g,u}id members of type vfs{g,u}id_t to struct iattr. We use
an anonymous union (similar to what we do in struct file) around
ia_{g,u}id and ia_vfs{g,u}id.
At the end of this series ia_{g,u}id and ia_vfs{g,u}id will always
contain the same value independent of whether struct iattr is
initialized from an idmapped mount. This is a change from how this is
done today.
Wrapping this in a anonymous unions has a few advantages. It allows us
to avoid needlessly increasing struct iattr. Since the types for
ia_{g,u}id and ia_vfs{g,u}id are structures with overlapping/identical
members they are covered by 6.5.2.3/6 of the C standard and it is safe
to initialize and access them.
Filesystems that raise FS_ALLOW_IDMAP and thus support idmapped mounts
will have to use ia_vfs{g,u}id and the associated helpers. And will be
ported at the end of this series. They will immediately benefit from the
type safe new helpers.
Filesystems that do not support FS_ALLOW_IDMAP can continue to use
ia_{g,u}id for now. The aim is to convert every filesystem to always use
ia_vfs{g,u}id and thus ultimately remove the ia_{g,u}id members.
Link: https://lore.kernel.org/r/20220621141454.2914719-4-brauner@kernel.org
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Reviewed-by: Seth Forshee <sforshee@digitalocean.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Introduces new vfs{g,u}id_t types. Similar to k{g,u}id_t the new types
are just simple wrapper structs around regular {g,u}id_t types.
They allows to establish a type safety boundary between {g,u}ids on
idmapped mounts and {g,u}ids as they are represented in filesystems
themselves.
A vfs{g,u}id_t is always created from a k{g,u}id_t, never directly from
a {g,u}id_t as idmapped mounts remap a given {g,u}id according to the
mount's idmapping. This is expressed in the VFS{G,U}IDT_INIT() macros.
A vfs{g,u}id_t may be used as a k{g,u}id_t via AS_K{G,U}IDT(). This
often happens when we need to check whether a {g,u}id mapped according
to an idmapped mount is identical to a given k{g,u}id_t. For an example,
see vfsgid_in_group_p() which determines whether the value of vfsgid_t
matches the value of any of the caller's groups. Similar logic is
expressed in the k{g,u}id_eq_vfs{g,u}id().
The from_vfs{g,u}id() helpers map a given vfs{g,u}id_t from the mount's
idmapping into the filesystem idmapping. They make it possible to update
a filesystem object such as inode->i_{g,u}id with the correct value.
This makes it harder to accidently write a wrong {g,u}id anwywhere. The
vfs{g,u}id_has_fsmapping() helpers check whether a given vfs{g,u}id_t
can be mapped into the filesystem idmapping.
All new helpers are nops on non-idmapped mounts.
I've done work on this roughly 7 months ago but dropped it to focus on
the testsuite. Linus brought this up independently just last week and
it's time to move this along (see [1]).
[1]: https://lore.kernel.org/lkml/CAHk-=win6+ahs1EwLkcq8apqLi_1wXFWbrPf340zYEhObpz4jA@mail.gmail.com
Link: https://lore.kernel.org/r/20220621141454.2914719-2-brauner@kernel.org
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Reviewed-by: Seth Forshee <sforshee@digitalocean.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Enable the mapped_fs{g,u}id() helpers to support filesystems mounted
with an idmapping. Apart from core mapping helpers that use
mapped_fs{g,u}id() to initialize struct inode's i_{g,u}id fields xfs is
the only place that uses these low-level helpers directly.
The patch only extends the helpers to be able to take the filesystem
idmapping into account. Since we don't actually yet pass the
filesystem's idmapping in no functional changes happen. This will happen
in a final patch.
Link: https://lore.kernel.org/r/20211123114227.3124056-9-brauner@kernel.org (v1)
Link: https://lore.kernel.org/r/20211130121032.3753852-9-brauner@kernel.org (v2)
Link: https://lore.kernel.org/r/20211203111707.3901969-9-brauner@kernel.org
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Seth Forshee <sforshee@digitalocean.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Currently we only support idmapped mounts for filesystems mounted
without an idmapping. This was a conscious decision mentioned in
multiple places (cf. e.g. [1]).
As explained at length in [3] it is perfectly fine to extend support for
idmapped mounts to filesystem's mounted with an idmapping should the
need arise. The need has been there for some time now. Various container
projects in userspace need this to run unprivileged and nested
unprivileged containers (cf. [2]).
Before we can port any filesystem that is mountable with an idmapping to
support idmapped mounts we need to first extend the mapping helpers to
account for the filesystem's idmapping. This again, is explained at
length in our documentation at [3] but I'll give an overview here again.
Currently, the low-level mapping helpers implement the remapping
algorithms described in [3] in a simplified manner. Because we could
rely on the fact that all filesystems supporting idmapped mounts are
mounted without an idmapping the translation step from or into the
filesystem idmapping could be skipped.
In order to support idmapped mounts of filesystem's mountable with an
idmapping the translation step we were able to skip before cannot be
skipped anymore. A filesystem mounted with an idmapping is very likely
to not use an identity mapping and will instead use a non-identity
mapping. So the translation step from or into the filesystem's idmapping
in the remapping algorithm cannot be skipped for such filesystems. More
details with examples can be found in [3].
This patch adds a few new and prepares some already existing low-level
mapping helpers to perform the full translation algorithm explained in
[3]. The low-level helpers can be written in a way that they only
perform the additional translation step when the filesystem is indeed
mounted with an idmapping.
If the low-level helpers detect that they are not dealing with an
idmapped mount they can simply return the relevant k{g,u}id unchanged;
no remapping needs to be performed at all. The no_idmapping() helper
detects whether the shortcut can be used.
If the low-level helpers detected that they are dealing with an idmapped
mount but the underlying filesystem is mounted without an idmapping we
can rely on the previous shorcut and can continue to skip the
translation step from or into the filesystem's idmapping.
These checks guarantee that only the minimal amount of work is
performed. As before, if idmapped mounts aren't used the low-level
helpers are idempotent and no work is performed at all.
This patch adds the helpers mapped_k{g,u}id_fs() and
mapped_k{g,u}id_user(). Following patches will port all places to
replace the old k{g,u}id_into_mnt() and k{g,u}id_from_mnt() with these
two new helpers. After the conversion is done k{g,u}id_into_mnt() and
k{g,u}id_from_mnt() will be removed. This also concludes the renaming of
the mapping helpers we started in [4]. Now, all mapping helpers will
started with the "mapped_" prefix making everything nice and consistent.
The mapped_k{g,u}id_fs() helpers replace the k{g,u}id_into_mnt()
helpers. They are to be used when k{g,u}ids are to be mapped from the
vfs, e.g. from from struct inode's i_{g,u}id. Conversely, the
mapped_k{g,u}id_user() helpers replace the k{g,u}id_from_mnt() helpers.
They are to be used when k{g,u}ids are to be written to disk, e.g. when
entering from a system call to change ownership of a file.
This patch only introduces the helpers. It doesn't yet convert the
relevant places to account for filesystem mounted with an idmapping.
[1]: commit 2ca4dcc490 ("fs/mount_setattr: tighten permission checks")
[2]: https://github.com/containers/podman/issues/10374
[3]: Documentations/filesystems/idmappings.rst
[4]: commit a65e58e791 ("fs: document and rename fsid helpers")
Link: https://lore.kernel.org/r/20211123114227.3124056-5-brauner@kernel.org (v1)
Link: https://lore.kernel.org/r/20211130121032.3753852-5-brauner@kernel.org (v2)
Link: https://lore.kernel.org/r/20211203111707.3901969-5-brauner@kernel.org
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Reviewed-by: Seth Forshee <sforshee@digitalocean.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
The low-level mapping helpers were so far crammed into fs.h. They are
out of place there. The fs.h header should just contain the higher-level
mapping helpers that interact directly with vfs objects such as struct
super_block or struct inode and not the bare mapping helpers. Similarly,
only vfs and specific fs code shall interact with low-level mapping
helpers. And so they won't be made accessible automatically through
regular {g,u}id helpers.
Link: https://lore.kernel.org/r/20211123114227.3124056-3-brauner@kernel.org (v1)
Link: https://lore.kernel.org/r/20211130121032.3753852-3-brauner@kernel.org (v2)
Link: https://lore.kernel.org/r/20211203111707.3901969-3-brauner@kernel.org
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Seth Forshee <sforshee@digitalocean.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
