net/ipv4/ip_gre.c in the Linux kernel before 2.6.34, when ip_gre is
configured as a module, allows remote attackers to cause a denial of
service (OOPS) by sending a packet during module loading.

It was discovered that the GRE protocol incorrectly handled netns
initialization. A remote attacker could send a packet while the ip_gre
module was loading, and crash the system, leading to a denial of service.