The mext_check_arguments function in fs/ext4/move_extent.c in the Linux kernel before 2.6.35 allows local users to overwrite an append-only file via a MOVE_EXT ioctl call that specifies this file as a donor.
https://bugzilla.redhat.com/show_bug.cgi?id=601006
http://www.vmware.com/security/advisories/VMSA-2011-0003.html
http://www.ubuntu.com/usn/USN-1000-1
http://www.securityfocus.com/archive/1/516397/100/0/threaded
http://www.openwall.com/lists/oss-security/2010/06/09/1
http://www.openwall.com/lists/oss-security/2010/06/07/1
http://lists.opensuse.org/opensuse-security-announce/2010-08/msg00000.html