net: add build-time checks for msg->msg_name size

This is a follow-up patch to f3d3342602 ("net: rework recvmsg
handler msg_name and msg_namelen logic").

DECLARE_SOCKADDR validates that the structure we use for writing the
name information to is not larger than the buffer which is reserved
for msg->msg_name (which is 128 bytes). Also use DECLARE_SOCKADDR
consistently in sendmsg code paths.

Signed-off-by: Steffen Hurrle <steffen@hurrle.net>
Suggested-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/isdn/mISDN/socket.c

@@ -135,7 +135,7 @@ mISDN_sock_recvmsg(struct kiocb *iocb, struct socket *sock,
 		return err;
 
 	if (msg->msg_name) {
-		struct sockaddr_mISDN *maddr = msg->msg_name;
+		DECLARE_SOCKADDR(struct sockaddr_mISDN *, maddr, msg->msg_name);
 
 		maddr->family = AF_ISDN;
 		maddr->dev = _pms(sk)->dev->id;
@@ -179,7 +179,6 @@ mISDN_sock_sendmsg(struct kiocb *iocb, struct socket *sock,
 	struct sock		*sk = sock->sk;
 	struct sk_buff		*skb;
 	int			err = -ENOMEM;
-	struct sockaddr_mISDN	*maddr;
 
 	if (*debug & DEBUG_SOCKET)
 		printk(KERN_DEBUG "%s: len %d flags %x ch %d proto %x\n",
@@ -214,7 +213,7 @@ mISDN_sock_sendmsg(struct kiocb *iocb, struct socket *sock,
 
 	if (msg->msg_namelen >= sizeof(struct sockaddr_mISDN)) {
 		/* if we have a address, we use it */
-		maddr = (struct sockaddr_mISDN *)msg->msg_name;
+		DECLARE_SOCKADDR(struct sockaddr_mISDN *, maddr, msg->msg_name);
 		mISDN_HEAD_ID(skb) = maddr->channel;
 	} else { /* use default for L2 messages */
 		if ((sk->sk_protocol == ISDN_P_LAPD_TE) ||