fs: port privilege checking helpers to mnt_idmap

Convert to struct mnt_idmap.

Last cycle we merged the necessary infrastructure in
256c8aed2b42 ("fs: introduce dedicated idmap type for mounts").
This is just the conversion to struct mnt_idmap.

Currently we still pass around the plain namespace that was attached to a
mount. This is in general pretty convenient but it makes it easy to
conflate namespaces that are relevant on the filesystem with namespaces
that are relevent on the mount level. Especially for non-vfs developers
without detailed knowledge in this area this can be a potential source for
bugs.

Once the conversion to struct mnt_idmap is done all helpers down to the
really low-level helpers will take a struct mnt_idmap argument instead of
two namespace arguments. This way it becomes impossible to conflate the two
eliminating the possibility of any bugs. All of the vfs and all filesystems
only operate on struct mnt_idmap.

Acked-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/kernel/capability.c b/kernel/capability.c
index 860fd22117c1..509a9cfb29f2 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -486,9 +486,11 @@ EXPORT_SYMBOL(file_ns_capable);
  * Return true if the inode uid and gid are within the namespace.
  */
 bool privileged_wrt_inode_uidgid(struct user_namespace *ns,
-				 struct user_namespace *mnt_userns,
+				 struct mnt_idmap *idmap,
 				 const struct inode *inode)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
+
 	return vfsuid_has_mapping(ns, i_uid_into_vfsuid(mnt_userns, inode)) &&
 	       vfsgid_has_mapping(ns, i_gid_into_vfsgid(mnt_userns, inode));
 }
@@ -502,13 +504,13 @@ bool privileged_wrt_inode_uidgid(struct user_namespace *ns,
  * its own user namespace and that the given inode's uid and gid are
  * mapped into the current user namespace.
  */
-bool capable_wrt_inode_uidgid(struct user_namespace *mnt_userns,
+bool capable_wrt_inode_uidgid(struct mnt_idmap *idmap,
 			      const struct inode *inode, int cap)
 {
 	struct user_namespace *ns = current_user_ns();
 
 	return ns_capable(ns, cap) &&
-	       privileged_wrt_inode_uidgid(ns, mnt_userns, inode);
+	       privileged_wrt_inode_uidgid(ns, idmap, inode);
 }
 EXPORT_SYMBOL(capable_wrt_inode_uidgid);