The cifs_close function in fs/cifs/file.c in the Linux kernel before 2.6.39 allows local users to cause a denial of service (NULL pointer dereference and BUG) or possibly have unspecified other impact by setting the O_DIRECT flag during an attempt to open a file on a CIFS filesystem.
http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.39
http://securityreason.com/securityalert/8367