Integer overflow in the uvm_map_isavail function in uvm/uvm_map.c in OpenBSD 5.9 allows local users to cause a denial of service (kernel panic) via a crafted mmap call, which triggers the new mapping to overlap with an existing mapping.
http://www.securityfocus.com/bid/92264
http://ftp.openbsd.org/pub/OpenBSD/patches/5.9/common/023_uvmisavail.patch.sig