This adds the STATMOUNT_MNT_UIDMAP and STATMOUNT_MNT_GIDMAP options.
It allows the retrieval of idmappings via statmount().
Currently it isn't possible to figure out what idmappings are applied to
an idmapped mount. This information is often crucial. Before statmount()
the only realistic options for an interface like this would have been to
add it to /proc/<pid>/fdinfo/<nr> or to expose it in
/proc/<pid>/mountinfo. Both solution would have been pretty ugly and
would've shown information that is of strong interest to some
application but not all. statmount() is perfect for this.
The idmappings applied to an idmapped mount are shown relative to the
caller's user namespace. This is the most useful solution that doesn't
risk leaking information or confuse the caller.
For example, an idmapped mount might have been created with the
following idmappings:
mount --bind -o X-mount.idmap="0:10000:1000 2000:2000:1 3000:3000:1" /srv /opt
Listing the idmappings through statmount() in the same context shows:
mnt_id: 2147485088
mnt_parent_id: 2147484816
fs_type: btrfs
mnt_root: /srv
mnt_point: /opt
mnt_opts: ssd,discard=async,space_cache=v2,subvolid=5,subvol=/
mnt_uidmap[0]: 0 10000 1000
mnt_uidmap[1]: 2000 2000 1
mnt_uidmap[2]: 3000 3000 1
mnt_gidmap[0]: 0 10000 1000
mnt_gidmap[1]: 2000 2000 1
mnt_gidmap[2]: 3000 3000 1
But the idmappings might not always be resolvable in the caller's user
namespace. For example:
unshare --user --map-root
In this case statmount() will skip any mappings that fil to resolve in
the caller's idmapping:
mnt_id: 2147485087
mnt_parent_id: 2147484016
fs_type: btrfs
mnt_root: /srv
mnt_point: /opt
mnt_opts: ssd,discard=async,space_cache=v2,subvolid=5,subvol=/
The caller can differentiate between a mount not being idmapped and a
mount that is idmapped but where all mappings fail to resolve in the
caller's idmapping by check for the STATMOUNT_MNT_{G,U}IDMAP flag being
raised but the number of mappings in ->mnt_{g,u}idmap_num being zero.
Note that statmount() requires that the whole range must be resolvable
in the caller's user namespace. If a subrange fails to map it will still
list the map as not resolvable. This is a practical compromise to avoid
having to find which subranges are resovable and wich aren't.
Idmappings are listed as a string array with each mapping separated by
zero bytes. This allows to retrieve the idmappings and immediately use
them for writing to e.g., /proc/<pid>/{g,u}id_map and it also allow for
simple iteration like:
if (stmnt->mask & STATMOUNT_MNT_UIDMAP) {
const char *idmap = stmnt->str + stmnt->mnt_uidmap;
for (size_t idx = 0; idx < stmnt->mnt_uidmap_nr; idx++) {
printf("mnt_uidmap[%lu]: %s\n", idx, idmap);
idmap += strlen(idmap) + 1;
}
}
Link: https://lore.kernel.org/r/20250204-work-mnt_idmap-statmount-v2-2-007720f39f2e@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
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Merge tag 'fuse-update-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse
Pull fuse updates from Miklos Szeredi:
- Add support for idmapped fuse mounts (Alexander Mikhalitsyn)
- Add optimization when checking for writeback (yangyun)
- Add tracepoints (Josef Bacik)
- Clean up writeback code (Joanne Koong)
- Clean up request queuing (me)
- Misc fixes
* tag 'fuse-update-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse: (32 commits)
fuse: use exclusive lock when FUSE_I_CACHE_IO_MODE is set
fuse: clear FR_PENDING if abort is detected when sending request
fs/fuse: convert to use invalid_mnt_idmap
fs/mnt_idmapping: introduce an invalid_mnt_idmap
fs/fuse: introduce and use fuse_simple_idmap_request() helper
fs/fuse: fix null-ptr-deref when checking SB_I_NOIDMAP flag
fuse: allow O_PATH fd for FUSE_DEV_IOC_BACKING_OPEN
virtio_fs: allow idmapped mounts
fuse: allow idmapped mounts
fuse: warn if fuse_access is called when idmapped mounts are allowed
fuse: handle idmappings properly in ->write_iter()
fuse: support idmapped ->rename op
fuse: support idmapped ->set_acl
fuse: drop idmap argument from __fuse_get_acl
fuse: support idmapped ->setattr op
fuse: support idmapped ->permission inode op
fuse: support idmapped getattr inode op
fuse: support idmap for mkdir/mknod/symlink/create/tmpfile
fuse: support idmapped FUSE_EXT_GROUPS
fuse: add an idmap argument to fuse_simple_request
...
Let the kememdup_array() take care about multiplication and possible
overflows.
v2:Add a new modification for reverse array.
Signed-off-by: Yu Jiaoliang <yujiaoliang@vivo.com>
Link: https://lore.kernel.org/r/20240823015542.3006262-1-yujiaoliang@vivo.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Currently, it is possible to create an idmapped mount using a user
namespace without any mappings. However, this yields an idmapped
mount that doesn't actually map the ids. With the following change,
it will no longer be possible to create an idmapped mount when using
a user namespace with no mappings, and will instead return EINVAL,
an “invalid argument” error code.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Taylor Jackson <taylor.a.jackson@me.com>
Link: https://lore.kernel.org/r/20240208-mnt-idmap-inval-v2-1-58ef26d194e0@me.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
There's no reason we need to couple mnt idmapping to namespaces in the
way we currently do. Copy the idmapping when an idmapped mount is
created and don't take any reference on the namespace at all.
We also can't easily refcount struct uid_gid_map because it needs to
stay the size of a cacheline otherwise we risk performance regressions
(Ignoring for a second that right now struct uid_gid_map isn't actually
64 byte but 72 but that's a fix for another patch series.).
Link: https://lore.kernel.org/r/20231122-vfs-mnt_idmap-v1-3-dae4abdde5bd@kernel.org
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
All mounts default to nop_mnt_idmap and we don't allow creating idmapped
mounts that reuse the idmapping of the filesystem. So unless someone
passes a non-superblock namespace to these helpers this check will
always be false. Remove it and replace it with a simple check for
nop_mnt_idmap.
Link: https://lore.kernel.org/r/20231122-vfs-mnt_idmap-v1-2-dae4abdde5bd@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
These helpers are required to support idmapped mounts in CephFS.
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Now that we converted everything to just rely on struct mnt_idmap move it all
into a separate file. This ensure that no code can poke around in struct
mnt_idmap without any dedicated helpers and makes it easier to extend it in the
future. Filesystems will now not be able to conflate mount and filesystem
idmappings as they are two distinct types and require distinct helpers that
cannot be used interchangeably. We are now also able to extend struct mnt_idmap
as we see fit.
Acked-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
