The Linux kernel before 3.12.4 updates certain length values before ensuring that associated data structures have been initialized, which allows local users to obtain sensitive information from kernel stack memory via a (1) recvfrom, (2) recvmmsg, or (3) recvmsg system call, related to net/ipv4/ping.c, net/ipv4/raw.c, net/ipv4/udp.c, net/ipv6/raw.c, and net/ipv6/udp.c.