The cifs_find_smb_ses function in fs/cifs/connect.c in the Linux kernel before 2.6.36 does not properly determine the associations between users and sessions, which allows local users to bypass CIFS share authentication by leveraging a mount of a share by a different user.
https://bugzilla.redhat.com/show_bug.cgi?id=697394
http://www.openwall.com/lists/oss-security/2011/04/15/8
http://lists.opensuse.org/opensuse-security-announce/2015-04/msg00020.html
http://ftp.osuosl.org/pub/linux/kernel/v2.6/ChangeLog-2.6.36