The (1) BMDMA and (2) AHCI HBA interfaces in the IDE functionality in QEMU 1.0 through 2.1.3 have multiple interpretations of a function's return value, which allows guest OS users to cause a host OS denial of service (memory consumption or infinite loop, and system crash) via a PRDT with zero complete sectors, related to the bmdma_prepare_buf and ahci_dma_prepare_buf functions.
http://www.securityfocus.com/bid/73316
http://www.debian.org/security/2015/dsa-3259
http://openwall.com/lists/oss-security/2015/04/20/7
http://git.qemu.org/?p=qemu.git%3Ba=commit%3Bh=3251bdcf1c67427d964517053c3d185b46e618e8