net/dns_resolver/dns_key.c in the Linux kernel before 2.6.38 allows remote DNS servers to cause a denial of service (NULL pointer dereference and OOPS) by not providing a valid response to a DNS query, as demonstrated by an erroneous grand.centrall.org query, which triggers improper handling of error data within a DNS resolver key.
http://openwall.com/lists/oss-security/2011/03/04/13
http://securitytracker.com/id?1025162
http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.38