Denying access from sb_umount issue

[Alexander Ivanov]

The lsm module implementes sb_umount() hook to disable lazy umounts. When access is denied, all consecutive umounts fail. It looks like mount reference count is messed up when sb_umount() return -EPERM. Is it possible that umount syscall assumes do_umount() touches those references and it calls 

 dput(path.dentry);
 mntput_no_expire(mnt);

regardless of what do_mount() returns?

Thanks,
--Alex