[PATCH] remount: mount flags filtering

 - we could pass MS_ACTIVE in mount flags and it would be passed into
   ->get_sb(), leading to interesting failure modes.  This flag is only
   for internal use (it's set once fill_super is complete and reset
   before the inode eviction on umount); made sure that we never get
   tricked into having it set it too early.

fs/namespace.c

@@ -777,7 +777,7 @@ long do_mount(char * dev_name, char * dir_name, char *type_page,
 		mnt_flags |= MNT_NODEV;
 	if (flags & MS_NOEXEC)
 		mnt_flags |= MNT_NOEXEC;
-	flags &= ~(MS_NOSUID|MS_NOEXEC|MS_NODEV);
+	flags &= ~(MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_ACTIVE);
 
 	/* ... and get the mountpoint */
 	retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);