The do_block_io_op function in (1) drivers/xen/blkback/blkback.c and (2) drivers/xen/blktap/blktap.c in Xen before 3.4.0 for the Linux kernel 2.6.18, and possibly other versions, allows guest OS users to cause a denial of service (infinite loop and CPU consumption) via a large production request index to the blkback or blktap back-end drivers. NOTE: some of these details are obtained from third party information.
https://bugzilla.redhat.com/show_bug.cgi?id=656206
http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/77f831cbb91d
http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/7070d34f251c
http://www.vupen.com/english/advisories/2011/0024
http://www.vmware.com/security/advisories/VMSA-2011-0012.html
http://www.securityfocus.com/bid/45029
http://www.securityfocus.com/archive/1/520102/100/0/threaded
http://www.redhat.com/support/errata/RHSA-2011-0004.html
http://www.openwall.com/lists/oss-security/2010/11/24/8
http://www.openwall.com/lists/oss-security/2010/11/23/1
http://secunia.com/advisories/46397