source: https://www.securityfocus.com/bid/13775/info

Both cryptoloop and dm-crypt are reported prone to an information disclosure vulnerability. Reports indicate that certain watermarked files may be detected on a filesystem that is encrypted using the affected loop device encryption schemes.

It should be noted that a successful attack would reveal the presence of a watermarked file but not the file contents. 

https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/25707.tar.bz2