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

This is a follow-up patch to f3d3342602f8bc ("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>
diff --git a/net/llc/af_llc.c b/net/llc/af_llc.c
index c71b699..0080d2b 100644
--- a/net/llc/af_llc.c
+++ b/net/llc/af_llc.c
@@ -707,7 +707,7 @@
 static int llc_ui_recvmsg(struct kiocb *iocb, struct socket *sock,
 			  struct msghdr *msg, size_t len, int flags)
 {
-	struct sockaddr_llc *uaddr = (struct sockaddr_llc *)msg->msg_name;
+	DECLARE_SOCKADDR(struct sockaddr_llc *, uaddr, msg->msg_name);
 	const int nonblock = flags & MSG_DONTWAIT;
 	struct sk_buff *skb = NULL;
 	struct sock *sk = sock->sk;
@@ -884,7 +884,7 @@
 {
 	struct sock *sk = sock->sk;
 	struct llc_sock *llc = llc_sk(sk);
-	struct sockaddr_llc *addr = (struct sockaddr_llc *)msg->msg_name;
+	DECLARE_SOCKADDR(struct sockaddr_llc *, addr, msg->msg_name);
 	int flags = msg->msg_flags;
 	int noblock = flags & MSG_DONTWAIT;
 	struct sk_buff *skb;