The parisc_show_stack function in arch/parisc/kernel/traps.c in the Linux kernel before 2.6.28-rc7 on PA-RISC allows local users to cause a denial of service (system crash) via vectors associated with an attempt to unwind a stack that contains userspace addresses.
https://exchange.xforce.ibmcloud.com/vulnerabilities/47075
http://www.ubuntu.com/usn/usn-715-1
http://www.securityfocus.com/bid/32636
http://www.debian.org/security/2009/dsa-1794
http://www.debian.org/security/2009/dsa-1787
http://secunia.com/advisories/35011
http://secunia.com/advisories/34981
http://secunia.com/advisories/33756
http://secunia.com/advisories/32933
http://marc.info/?l=linux-parisc&m=121736357203624&w=2
http://kernel.org/pub/linux/kernel/v2.6/testing/ChangeLog-2.6.28-rc7