The dispatch_discard_io function in drivers/block/xen-blkback/blkback.c in the Xen blkback implementation in the Linux kernel before 3.10.5 allows guest OS users to cause a denial of service (data loss) via filesystem write operations on a read-only disk that supports the (1) BLKIF_OP_DISCARD (aka discard or TRIM) or (2) SCSI UNMAP feature.
https://bugzilla.redhat.com/show_bug.cgi?id=971146
https://github.com/torvalds/linux/commit/604c499cbbcc3d5fe5fb8d53306aa0fae1990109
http://www.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.10.5
http://www.openwall.com/lists/oss-security/2013/06/05/21
http://www.ubuntu.com/usn/USN-1938-1
http://www.ubuntu.com/usn/USN-1943-1
http://www.ubuntu.com/usn/USN-1944-1
http://www.ubuntu.com/usn/USN-1945-1
http://www.ubuntu.com/usn/USN-1946-1
http://www.ubuntu.com/usn/USN-1947-1