inet: prevent leakage of uninitialized memory to user in recv syscalls

Only update *addr_len when we actually fill in sockaddr, otherwise we
can return uninitialized memory from the stack to the caller in the
recvfrom, recvmmsg and recvmsg syscalls. Drop the the (addr_len == NULL)
checks because we only get called with a valid addr_len pointer either
from sock_common_recvmsg or inet_recvmsg.

If a blocking read waits on a socket which is concurrently shut down we
now return zero and set msg_msgnamelen to 0.

Reported-by: mpb <mpb.mail@gmail.com>
Suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
static int __net_init raw6_init_net(struct net *net)
{
	if (!proc_create("raw6", S_IRUGO, net->proc_net, &raw6_seq_fops))
		return -ENOMEM;

	return 0;
}

static int __net_init raw6_init_net(struct net *net)
{
	if (!proc_create("raw6", S_IRUGO, net->proc_net, &raw6_seq_fops))
		return -ENOMEM;

	return 0;
}
