net: sockets: Fix sendmsg() user mode param checks for dst address

If we are calling sendmsg() for a connected socket, then msg_namelen
is 0 and msg_name is NULL. Check these allowed values properly.

Also modify unit tests so that we test this scenario.

Fixes #25925

Signed-off-by: Jukka Rissanen <[email protected]>

Author: jukkar

subsys/net/lib/sockets/sockets.c

@@ -643,11 +643,13 @@ static inline ssize_t z_vrfy_zsock_sendmsg(int sock,
 		msg_copy.msg_iov[i].iov_len = msg->msg_iov[i].iov_len;
 	}
 
-	msg_copy.msg_name = z_user_alloc_from_copy(msg->msg_name,
-						   msg->msg_namelen);
-	if (!msg_copy.msg_name) {
-		errno = ENOMEM;
-		goto fail;
+	if (msg->msg_namelen > 0) {
+		msg_copy.msg_name = z_user_alloc_from_copy(msg->msg_name,
+							   msg->msg_namelen);
+		if (!msg_copy.msg_name) {
+			errno = ENOMEM;
+			goto fail;
+		}
 	}
 
 	msg_copy.msg_control = z_user_alloc_from_copy(msg->msg_control,

tests/net/socket/udp/src/main.c

@@ -572,8 +572,6 @@ void test_v4_sendmsg_recvfrom_connected(void)
 	msg.msg_controllen = sizeof(cmsgbuf.buf);
 	msg.msg_iov = io_vector;
 	msg.msg_iovlen = 1;
-	msg.msg_name = &server_addr;
-	msg.msg_namelen = sizeof(server_addr);
 
 	cmsg = CMSG_FIRSTHDR(&msg);
 	cmsg->cmsg_len = CMSG_LEN(sizeof(int));
@@ -636,8 +634,6 @@ void test_v6_sendmsg_recvfrom_connected(void)
 	msg.msg_controllen = sizeof(cmsgbuf.buf);
 	msg.msg_iov = io_vector;
 	msg.msg_iovlen = 1;
-	msg.msg_name = &server_addr;
-	msg.msg_namelen = sizeof(server_addr);
 
 	cmsg = CMSG_FIRSTHDR(&msg);
 	cmsg->cmsg_len = CMSG_LEN(sizeof(int));