fs: port i_{g,u}id_into_vfs{g,u}id() to mnt_idmap

Convert to struct mnt_idmap.
Remove legacy file_mnt_user_ns() and mnt_user_ns().

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>

2 files changed, 14 insertions, 24 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3611d459bf88..173c5274a63a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1632,16 +1632,17 @@ static inline void i_gid_write(struct inode *inode, gid_t gid)
 }
 
 /**
- * i_uid_into_vfsuid - map an inode's i_uid down into a mnt_userns
- * @mnt_userns: user namespace of the mount the inode was found from
+ * i_uid_into_vfsuid - map an inode's i_uid down according to an idmapping
+ * @idmap: idmap of the mount the inode was found from
  * @inode: inode to map
  *
- * Return: whe inode's i_uid mapped down according to @mnt_userns.
+ * Return: whe inode's i_uid mapped down according to @idmap.
  * If the inode's i_uid has no mapping INVALID_VFSUID is returned.
  */
-static inline vfsuid_t i_uid_into_vfsuid(struct user_namespace *mnt_userns,
+static inline vfsuid_t i_uid_into_vfsuid(struct mnt_idmap *idmap,
 					 const struct inode *inode)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	return make_vfsuid(mnt_userns, i_user_ns(inode), inode->i_uid);
 }
 
@@ -1660,11 +1661,9 @@ static inline bool i_uid_needs_update(struct mnt_idmap *idmap,
 				      const struct iattr *attr,
 				      const struct inode *inode)
 {
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
-
 	return ((attr->ia_valid & ATTR_UID) &&
 		!vfsuid_eq(attr->ia_vfsuid,
-			   i_uid_into_vfsuid(mnt_userns, inode)));
+			   i_uid_into_vfsuid(idmap, inode)));
 }
 
 /**
@@ -1688,16 +1687,17 @@ static inline void i_uid_update(struct mnt_idmap *idmap,
 }
 
 /**
- * i_gid_into_vfsgid - map an inode's i_gid down into a mnt_userns
- * @mnt_userns: user namespace of the mount the inode was found from
+ * i_gid_into_vfsgid - map an inode's i_gid down according to an idmapping
+ * @idmap: idmap of the mount the inode was found from
  * @inode: inode to map
  *
- * Return: the inode's i_gid mapped down according to @mnt_userns.
+ * Return: the inode's i_gid mapped down according to @idmap.
  * If the inode's i_gid has no mapping INVALID_VFSGID is returned.
  */
-static inline vfsgid_t i_gid_into_vfsgid(struct user_namespace *mnt_userns,
+static inline vfsgid_t i_gid_into_vfsgid(struct mnt_idmap *idmap,
 					 const struct inode *inode)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	return make_vfsgid(mnt_userns, i_user_ns(inode), inode->i_gid);
 }
 
@@ -1716,11 +1716,9 @@ static inline bool i_gid_needs_update(struct mnt_idmap *idmap,
 				      const struct iattr *attr,
 				      const struct inode *inode)
 {
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
-
 	return ((attr->ia_valid & ATTR_GID) &&
 		!vfsgid_eq(attr->ia_vfsgid,
-			   i_gid_into_vfsgid(mnt_userns, inode)));
+			   i_gid_into_vfsgid(idmap, inode)));
 }
 
 /**
@@ -2334,10 +2332,8 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
 static inline bool HAS_UNMAPPED_ID(struct mnt_idmap *idmap,
 				   struct inode *inode)
 {
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
-
-	return !vfsuid_valid(i_uid_into_vfsuid(mnt_userns, inode)) ||
-	       !vfsgid_valid(i_gid_into_vfsgid(mnt_userns, inode));
+	return !vfsuid_valid(i_uid_into_vfsuid(idmap, inode)) ||
+	       !vfsgid_valid(i_gid_into_vfsgid(idmap, inode));
 }
 
 static inline void init_sync_kiocb(struct kiocb *kiocb, struct file *filp)
@@ -2732,11 +2728,6 @@ struct filename {
 };
 static_assert(offsetof(struct filename, iname) % sizeof(long) == 0);
 
-static inline struct user_namespace *file_mnt_user_ns(struct file *file)
-{
-	return mnt_user_ns(file->f_path.mnt);
-}
-
 static inline struct mnt_idmap *file_mnt_idmap(struct file *file)
 {
 	return mnt_idmap(file->f_path.mnt);
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 62475996fac6..02db5909d5c2 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -74,7 +74,6 @@ struct vfsmount {
 	struct mnt_idmap *mnt_idmap;
 } __randomize_layout;
 
-struct user_namespace *mnt_user_ns(const struct vfsmount *mnt);
 struct user_namespace *mnt_idmap_owner(const struct mnt_idmap *idmap);
 static inline struct mnt_idmap *mnt_idmap(const struct vfsmount *mnt)
 {