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/x25/af_x25.c b/net/x25/af_x25.c
index c8a8297..6177479 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -1082,7 +1082,7 @@
 {
 	struct sock *sk = sock->sk;
 	struct x25_sock *x25 = x25_sk(sk);
-	struct sockaddr_x25 *usx25 = (struct sockaddr_x25 *)msg->msg_name;
+	DECLARE_SOCKADDR(struct sockaddr_x25 *, usx25, msg->msg_name);
 	struct sockaddr_x25 sx25;
 	struct sk_buff *skb;
 	unsigned char *asmptr;
@@ -1258,7 +1258,7 @@
 {
 	struct sock *sk = sock->sk;
 	struct x25_sock *x25 = x25_sk(sk);
-	struct sockaddr_x25 *sx25 = (struct sockaddr_x25 *)msg->msg_name;
+	DECLARE_SOCKADDR(struct sockaddr_x25 *, sx25, msg->msg_name);
 	size_t copied;
 	int qbit, header_len;
 	struct sk_buff *skb;