mnt_idmapping: remove check_fsmapping()

The helper is a bit pointless. Just open-code the check.

Link: https://lore.kernel.org/r/20231122-vfs-mnt_idmap-v1-1-dae4abdde5bd@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/mnt_idmapping.c

@@ -25,19 +25,6 @@ struct mnt_idmap nop_mnt_idmap = {
 };
 EXPORT_SYMBOL_GPL(nop_mnt_idmap);
 
-/**
- * check_fsmapping - check whether an mount idmapping is allowed
- * @idmap: idmap of the relevent mount
- * @sb:    super block of the filesystem
- *
- * Return: true if @idmap is allowed, false if not.
- */
-bool check_fsmapping(const struct mnt_idmap *idmap,
-		     const struct super_block *sb)
-{
-	return idmap->owner != sb->s_user_ns;
-}
-
 /**
  * initial_idmapping - check whether this is the initial mapping
  * @ns: idmapping to check
@@ -94,8 +81,8 @@ static inline bool no_idmapping(const struct user_namespace *mnt_userns,
  */
 
 vfsuid_t make_vfsuid(struct mnt_idmap *idmap,
-				   struct user_namespace *fs_userns,
-				   kuid_t kuid)
+		     struct user_namespace *fs_userns,
+		     kuid_t kuid)
 {
 	uid_t uid;
 	struct user_namespace *mnt_userns = idmap->owner;

fs/namespace.c

@@ -4289,7 +4289,7 @@ static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
 	 * Creating an idmapped mount with the filesystem wide idmapping
 	 * doesn't make sense so block that. We don't allow mushy semantics.
 	 */
-	if (!check_fsmapping(kattr->mnt_idmap, m->mnt_sb))
+	if (kattr->mnt_userns == m->mnt_sb->s_user_ns)
 		return -EINVAL;
 
 	/*

include/linux/mnt_idmapping.h

@@ -244,7 +244,4 @@ static inline kgid_t mapped_fsgid(struct mnt_idmap *idmap,
 	return from_vfsgid(idmap, fs_userns, VFSGIDT_INIT(current_fsgid()));
 }
 
-bool check_fsmapping(const struct mnt_idmap *idmap,
-		     const struct super_block *sb);
-
 #endif /* _LINUX_MNT_IDMAPPING_H */