The do_sigaltstack function in kernel/signal.c in Linux kernel 2.4 through 2.4.37 and 2.6 before 2.6.31-rc5, when running on 64-bit systems, does not clear certain padding bytes from a structure, which allows local users to obtain sensitive information from the kernel stack via the sigaltstack function.
https://www.redhat.com/archives/fedora-package-announce/2009-August/msg01256.html
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A8405
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10637
https://bugzilla.redhat.com/show_bug.cgi?id=515392
http://www.vupen.com/english/advisories/2009/3316
http://www.vmware.com/security/advisories/VMSA-2009-0016.html
http://www.ubuntu.com/usn/USN-852-1
http://www.securityfocus.com/archive/1/507985/100/0/threaded
http://www.redhat.com/support/errata/RHSA-2009-1438.html
http://www.openwall.com/lists/oss-security/2009/08/26/2
http://www.openwall.com/lists/oss-security/2009/08/05/1
http://www.openwall.com/lists/oss-security/2009/08/04/1
http://www.exploit-db.com/exploits/9352
http://secunia.com/advisories/37471
http://secunia.com/advisories/37105
http://secunia.com/advisories/36759
http://secunia.com/advisories/36562
http://secunia.com/advisories/36501
http://secunia.com/advisories/36136