ovl: handle idmapped mounts in ovl_setattr()

Pass the mount's struct mnt_idmap to setattr_prepare() so that the
permission checks for a chown/chmod performed through an idmapped
overlay mount are evaluated in the mount's id space.

The ownership requested in @attr is expressed relative to the overlay
mount idmap.  Before forwarding the change to the upper layer via
ovl_do_notify_change() - whose notify_change() applies the upper layer
idmap in turn - rebase ia_vfsuid/ia_vfsgid into the overlay's own id
space, i.e. the same space as the overlay inode's i_{u,g}id established
by ovl_copyattr().  Without this rebase the upper layer would interpret
the caller's mount-relative id as an upper-relative one and store the
wrong owner on disk, or reject it with -EOVERFLOW.

from_vfsuid() returns INVALID_UID for an id that the overlay mount
idmap does not map; that invalid id is carried faithfully into the
forwarded iattr and rejected by the upper notify_change() via
vfsuid_has_fsmapping(), so no bogus owner can be written.

No functional change until FS_ALLOW_IDMAP is set on ovl_fs_type; until
then the overlay mount idmap is &nop_mnt_idmap and from_vfsuid() is the
identity.

Link: https://patch.msgid.link/20260615-work-idmapped-overlayfs-v1-3-7381632aa402@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions