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.
http://ftp.osuosl.org/pub/linux/kernel/v2.6/ChangeLog-2.6.36
http://lists.opensuse.org/opensuse-security-announce/2015-04/msg00020.html
http://www.openwall.com/lists/oss-security/2011/04/15/8
https://bugzilla.redhat.com/show_bug.cgi?id=697394
https://github.com/torvalds/linux/commit/4ff67b720c02c36e54d55b88c2931879b7db1cd2