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 dgram_bind(struct sock *sk, struct sockaddr *uaddr, int len)
{
	struct sockaddr_ieee802154 *addr = (struct sockaddr_ieee802154 *)uaddr;
	struct dgram_sock *ro = dgram_sk(sk);
	int err = -EINVAL;
	struct net_device *dev;

	lock_sock(sk);

	ro->bound = 0;

	if (len < sizeof(*addr))
		goto out;

	if (addr->family != AF_IEEE802154)
		goto out;

	dev = ieee802154_get_dev(sock_net(sk), &addr->addr);
	if (!dev) {
		err = -ENODEV;
		goto out;
	}

	if (dev->type != ARPHRD_IEEE802154) {
		err = -ENODEV;
		goto out_put;
	}

	memcpy(&ro->src_addr, &addr->addr, sizeof(struct ieee802154_addr));

	ro->bound = 1;
	err = 0;
out_put:
	dev_put(dev);
out:
	release_sock(sk);

	return err;
}

static int dgram_bind(struct sock *sk, struct sockaddr *uaddr, int len)
{
	struct sockaddr_ieee802154 *addr = (struct sockaddr_ieee802154 *)uaddr;
	struct dgram_sock *ro = dgram_sk(sk);
	int err = -EINVAL;
	struct net_device *dev;

	lock_sock(sk);

	ro->bound = 0;

	if (len < sizeof(*addr))
		goto out;

	if (addr->family != AF_IEEE802154)
		goto out;

	dev = ieee802154_get_dev(sock_net(sk), &addr->addr);
	if (!dev) {
		err = -ENODEV;
		goto out;
	}

	if (dev->type != ARPHRD_IEEE802154) {
		err = -ENODEV;
		goto out_put;
	}

	memcpy(&ro->src_addr, &addr->addr, sizeof(struct ieee802154_addr));

	ro->bound = 1;
	err = 0;
out_put:
	dev_put(dev);
out:
	release_sock(sk);

	return err;
}
