kernel: ipv6: fix ip6_dst_lookup_tail() NULL pointer dereference

The ip6dstlookuptail function in net/ipv6/ip6output.c in the Linux kernel before 2.6.27 does not properly handle certain circumstances involving an IPv6 TUN network interface and a large number of neighbors, which allows attackers to cause a denial of service NULL pointer dereference and OOPS or...