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 icmp_filter(const struct sock *sk, const struct sk_buff *skb)
{
	struct icmphdr _hdr;
	const struct icmphdr *hdr;

	hdr = skb_header_pointer(skb, skb_transport_offset(skb),
				 sizeof(_hdr), &_hdr);
	if (!hdr)
		return 1;

	if (hdr->type < 32) {
		__u32 data = raw_sk(sk)->filter.data;

		return ((1U << hdr->type) & data) != 0;
	}

	/* Do not block unknown ICMP types */
	return 0;
}

static int icmp_filter(const struct sock *sk, const struct sk_buff *skb)
{
	struct icmphdr _hdr;
	const struct icmphdr *hdr;

	hdr = skb_header_pointer(skb, skb_transport_offset(skb),
				 sizeof(_hdr), &_hdr);
	if (!hdr)
		return 1;

	if (hdr->type < 32) {
		__u32 data = raw_sk(sk)->filter.data;

		return ((1U << hdr->type) & data) != 0;
	}

	/* Do not block unknown ICMP types */
	return 0;
}
