[PATCH v3 3/3] ovl: validate superblock in OVL_FS()

[Andrea Righi]

When CONFIG_OVERLAY_FS_DEBUG is enabled add an explicit check to make
sure that OVL_FS() is always used with a valid overlayfs superblock.
Otherwise trigger a WARN_ON_ONCE().

Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Andrea Righi <andrea.righi@xxxxxxxxxxxxx>
---
 fs/overlayfs/ovl_entry.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index b32c38fdf3c7..e156649d9c71 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -97,8 +97,20 @@ static inline struct mnt_idmap *ovl_upper_mnt_idmap(struct ovl_fs *ofs)
 
 extern struct file_system_type ovl_fs_type;
 
+static inline bool is_ovl_fs_sb(struct super_block *sb)
+{
+	return sb->s_type == &ovl_fs_type;
+}
+
+#ifdef CONFIG_OVERLAY_FS_DEBUG
+#define OVL_VALIDATE_SB(__sb)	WARN_ON_ONCE(!is_ovl_fs_sb(__sb))
+#else
+#define OVL_VALIDATE_SB(__sb)
+#endif
+
 static inline struct ovl_fs *OVL_FS(struct super_block *sb)
 {
+	OVL_VALIDATE_SB(sb);
 	return (struct ovl_fs *)sb->s_fs_info;
 }
 
-- 
2.39.2