net: rework recvmsg handler msg_name and msg_namelen logic

This patch now always passes msg->msg_namelen as 0. recvmsg handlers must
set msg_namelen to the proper size <= sizeof(struct sockaddr_storage)
to return msg_name to the user.

This prevents numerous uninitialized memory leaks we had in the
recvmsg handlers and makes it harder for new code to accidentally leak
uninitialized memory.

Optimize for the case recvfrom is called with NULL as address. We don't
need to copy the address at all, so set it to NULL before invoking the
recvmsg handler. We can do so, because all the recvmsg handlers must
cope with the case a plain read() is called on them. read() also sets
msg_name to NULL.

Also document these changes in include/linux/net.h as suggested by David
Miller.

Changes since RFC:

Set msg->msg_name = NULL if user specified a NULL in msg_name but had a
non-null msg_namelen in verify_iovec/verify_compat_iovec. This doesn't
affect sendto as it would bail out earlier while trying to copy-in the
address. It also more naturally reflects the logic by the callers of
verify_iovec.

With this change in place I could remove "
if (!uaddr || msg_sys->msg_namelen == 0)
	msg->msg_name = NULL
".

This change does not alter the user visible error logic as we ignore
msg_namelen as long as msg_name is NULL.

Also remove two unnecessary curly brackets in ___sys_recvmsg and change
comments to netdev style.

Cc: David Miller <davem@davemloft.net>
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>
int ipxitf_send(struct ipx_interface *intrfc, struct sk_buff *skb, char *node)
{
	struct ipxhdr *ipx = ipx_hdr(skb);
	struct net_device *dev = intrfc->if_dev;
	struct datalink_proto *dl = intrfc->if_dlink;
	char dest_node[IPX_NODE_LEN];
	int send_to_wire = 1;
	int addr_len;

	ipx->ipx_tctrl = IPX_SKB_CB(skb)->ipx_tctrl;
	ipx->ipx_dest.net = IPX_SKB_CB(skb)->ipx_dest_net;
	ipx->ipx_source.net = IPX_SKB_CB(skb)->ipx_source_net;

	/* see if we need to include the netnum in the route list */
	if (IPX_SKB_CB(skb)->last_hop.index >= 0) {
		__be32 *last_hop = (__be32 *)(((u8 *) skb->data) +
				sizeof(struct ipxhdr) +
				IPX_SKB_CB(skb)->last_hop.index *
				sizeof(__be32));
		*last_hop = IPX_SKB_CB(skb)->last_hop.netnum;
		IPX_SKB_CB(skb)->last_hop.index = -1;
	}

	/*
	 * We need to know how many skbuffs it will take to send out this
	 * packet to avoid unnecessary copies.
	 */

	if (!dl || !dev || dev->flags & IFF_LOOPBACK)
		send_to_wire = 0;	/* No non looped */

	/*
	 * See if this should be demuxed to sockets on this interface
	 *
	 * We want to ensure the original was eaten or that we only use
	 * up clones.
	 */

	if (ipx->ipx_dest.net == intrfc->if_netnum) {
		/*
		 * To our own node, loop and free the original.
		 * The internal net will receive on all node address.
		 */
		if (intrfc == ipx_internal_net ||
		    !memcmp(intrfc->if_node, node, IPX_NODE_LEN)) {
			/* Don't charge sender */
			skb_orphan(skb);

			/* Will charge receiver */
			return ipxitf_demux_socket(intrfc, skb, 0);
		}

		/* Broadcast, loop and possibly keep to send on. */
		if (!memcmp(ipx_broadcast_node, node, IPX_NODE_LEN)) {
			if (!send_to_wire)
				skb_orphan(skb);
			ipxitf_demux_socket(intrfc, skb, send_to_wire);
			if (!send_to_wire)
				goto out;
		}
	}

	/*
	 * If the originating net is not equal to our net; this is routed
	 * We are still charging the sender. Which is right - the driver
	 * free will handle this fairly.
	 */
	if (ipx->ipx_source.net != intrfc->if_netnum) {
		/*
		 * Unshare the buffer before modifying the count in
		 * case it's a flood or tcpdump
		 */
		skb = skb_unshare(skb, GFP_ATOMIC);
		if (!skb)
			goto out;
		if (++ipx->ipx_tctrl > ipxcfg_max_hops)
			send_to_wire = 0;
	}

	if (!send_to_wire) {
		kfree_skb(skb);
		goto out;
	}

	/* Determine the appropriate hardware address */
	addr_len = dev->addr_len;
	if (!memcmp(ipx_broadcast_node, node, IPX_NODE_LEN))
		memcpy(dest_node, dev->broadcast, addr_len);
	else
		memcpy(dest_node, &(node[IPX_NODE_LEN-addr_len]), addr_len);

	/* Make any compensation for differing physical/data link size */
	skb = ipxitf_adjust_skbuff(intrfc, skb);
	if (!skb)
		goto out;

	/* set up data link and physical headers */
	skb->dev	= dev;
	skb->protocol	= htons(ETH_P_IPX);

	/* Send it out */
	dl->request(dl, skb, dest_node);
out:
	return 0;
}

int ipxitf_send(struct ipx_interface *intrfc, struct sk_buff *skb, char *node)
{
	struct ipxhdr *ipx = ipx_hdr(skb);
	struct net_device *dev = intrfc->if_dev;
	struct datalink_proto *dl = intrfc->if_dlink;
	char dest_node[IPX_NODE_LEN];
	int send_to_wire = 1;
	int addr_len;

	ipx->ipx_tctrl = IPX_SKB_CB(skb)->ipx_tctrl;
	ipx->ipx_dest.net = IPX_SKB_CB(skb)->ipx_dest_net;
	ipx->ipx_source.net = IPX_SKB_CB(skb)->ipx_source_net;

	/* see if we need to include the netnum in the route list */
	if (IPX_SKB_CB(skb)->last_hop.index >= 0) {
		__be32 *last_hop = (__be32 *)(((u8 *) skb->data) +
				sizeof(struct ipxhdr) +
				IPX_SKB_CB(skb)->last_hop.index *
				sizeof(__be32));
		*last_hop = IPX_SKB_CB(skb)->last_hop.netnum;
		IPX_SKB_CB(skb)->last_hop.index = -1;
	}

	/*
	 * We need to know how many skbuffs it will take to send out this
	 * packet to avoid unnecessary copies.
	 */

	if (!dl || !dev || dev->flags & IFF_LOOPBACK)
		send_to_wire = 0;	/* No non looped */

	/*
	 * See if this should be demuxed to sockets on this interface
	 *
	 * We want to ensure the original was eaten or that we only use
	 * up clones.
	 */

	if (ipx->ipx_dest.net == intrfc->if_netnum) {
		/*
		 * To our own node, loop and free the original.
		 * The internal net will receive on all node address.
		 */
		if (intrfc == ipx_internal_net ||
		    !memcmp(intrfc->if_node, node, IPX_NODE_LEN)) {
			/* Don't charge sender */
			skb_orphan(skb);

			/* Will charge receiver */
			return ipxitf_demux_socket(intrfc, skb, 0);
		}

		/* Broadcast, loop and possibly keep to send on. */
		if (!memcmp(ipx_broadcast_node, node, IPX_NODE_LEN)) {
			if (!send_to_wire)
				skb_orphan(skb);
			ipxitf_demux_socket(intrfc, skb, send_to_wire);
			if (!send_to_wire)
				goto out;
		}
	}

	/*
	 * If the originating net is not equal to our net; this is routed
	 * We are still charging the sender. Which is right - the driver
	 * free will handle this fairly.
	 */
	if (ipx->ipx_source.net != intrfc->if_netnum) {
		/*
		 * Unshare the buffer before modifying the count in
		 * case it's a flood or tcpdump
		 */
		skb = skb_unshare(skb, GFP_ATOMIC);
		if (!skb)
			goto out;
		if (++ipx->ipx_tctrl > ipxcfg_max_hops)
			send_to_wire = 0;
	}

	if (!send_to_wire) {
		kfree_skb(skb);
		goto out;
	}

	/* Determine the appropriate hardware address */
	addr_len = dev->addr_len;
	if (!memcmp(ipx_broadcast_node, node, IPX_NODE_LEN))
		memcpy(dest_node, dev->broadcast, addr_len);
	else
		memcpy(dest_node, &(node[IPX_NODE_LEN-addr_len]), addr_len);

	/* Make any compensation for differing physical/data link size */
	skb = ipxitf_adjust_skbuff(intrfc, skb);
	if (!skb)
		goto out;

	/* set up data link and physical headers */
	skb->dev	= dev;
	skb->protocol	= htons(ETH_P_IPX);

	/* Send it out */
	dl->request(dl, skb, dest_node);
out:
	return 0;
}
