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/rds/recv.c b/net/rds/recv.c
index de339b2..bd82522 100644
--- a/net/rds/recv.c
+++ b/net/rds/recv.c
@@ -402,7 +402,7 @@
 	struct rds_sock *rs = rds_sk_to_rs(sk);
 	long timeo;
 	int ret = 0, nonblock = msg_flags & MSG_DONTWAIT;
-	struct sockaddr_in *sin;
+	DECLARE_SOCKADDR(struct sockaddr_in *, sin, msg->msg_name);
 	struct rds_incoming *inc = NULL;
 
 	/* udp_recvmsg()->sock_recvtimeo() gets away without locking too.. */
@@ -479,7 +479,6 @@
 
 		rds_stats_inc(s_recv_delivered);
 
-		sin = (struct sockaddr_in *)msg->msg_name;
 		if (sin) {
 			sin->sin_family = AF_INET;
 			sin->sin_port = inc->i_hdr.h_sport;
diff --git a/net/rds/send.c b/net/rds/send.c
index 88eace5..a82fb66 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -922,7 +922,7 @@
 {
 	struct sock *sk = sock->sk;
 	struct rds_sock *rs = rds_sk_to_rs(sk);
-	struct sockaddr_in *usin = (struct sockaddr_in *)msg->msg_name;
+	DECLARE_SOCKADDR(struct sockaddr_in *, usin, msg->msg_name);
 	__be32 daddr;
 	__be16 dport;
 	struct rds_message *rm = NULL;