The xfs_fs_geometry function in fs/xfs/xfs_fsops.c in the Linux kernel before 2.6.38-rc6-git3 does not initialize a certain structure member, which allows local users to obtain potentially sensitive information from kernel stack memory via an FSGEOMETRY_V1 ioctl call.
http://openwall.com/lists/oss-security/2011/02/16/10
http://openwall.com/lists/oss-security/2011/02/16/4
http://rhn.redhat.com/errata/RHSA-2011-0927.html
http://www.kernel.org/pub/linux/kernel/v2.6/snapshots/patch-2.6.38-rc6-git3.log
http://www.securityfocus.com/bid/46417