Kernel: net: information leak in recvmsg handler msg_name & msg_namelen logic

The packetrecvmsg function in net/packet/afpacket.c in the Linux kernel before 3.12.4 updates a certain length value before ensuring that an associated data structure has been initialized, which allows local users to obtain sensitive information from kernel memory via a 1 recvfrom, 2 recvmmsg, or...