Check for message truncation in RADIUS client

The RADIUS client currently determines if a radius message is longer
than the supported maximum length by checking whether the size of the
received buffer and the length of the buffer (as returned by recv()) is
equal. This method fails to detect if the buffer has actually been
truncated. This change modifies the RADIUS client to instead use the
recvmsg() call and then check the message header flags to determine
whether or not the received message has been truncated and drop the
message if that is the case.

Signed-off-by: Anusha Datar <anusha@meter.com>
Reviewed-by: Steve deRosier <derosier@cal-sierra.com>
Reviewed-by: Julian Squires <julian@cipht.net>

src/radius/radius_client.c

@@ -816,7 +816,9 @@ static void radius_client_receive(int sock, void *eloop_ctx, void *sock_ctx)
 	struct hostapd_radius_servers *conf = radius->conf;
 	RadiusType msg_type = (RadiusType) sock_ctx;
 	int len, roundtrip;
-	unsigned char buf[RADIUS_MAX_MSG_LEN + 1];
+	unsigned char buf[RADIUS_MAX_MSG_LEN];
+	struct msghdr msghdr = {0};
+	struct iovec iov;
 	struct radius_msg *msg;
 	struct radius_hdr *hdr;
 	struct radius_rx_handler *handlers;
@@ -836,15 +838,22 @@ static void radius_client_receive(int sock, void *eloop_ctx, void *sock_ctx)
 		rconf = conf->auth_server;
 	}
 
-	len = recv(sock, buf, sizeof(buf), MSG_DONTWAIT);
+	iov.iov_base = buf;
+	iov.iov_len = RADIUS_MAX_MSG_LEN;
+	msghdr.msg_iov = &iov;
+	msghdr.msg_iovlen = 1;
+	msghdr.msg_flags = 0;
+	len = recvmsg(sock, &msghdr, MSG_DONTWAIT);
 	if (len < 0) {
-		wpa_printf(MSG_INFO, "recv[RADIUS]: %s", strerror(errno));
+		wpa_printf(MSG_INFO, "recvmsg[RADIUS]: %s", strerror(errno));
 		return;
 	}
+
 	hostapd_logger(radius->ctx, NULL, HOSTAPD_MODULE_RADIUS,
 		       HOSTAPD_LEVEL_DEBUG, "Received %d bytes from RADIUS "
 		       "server", len);
-	if (len == sizeof(buf)) {
+
+	if (msghdr.msg_flags & MSG_TRUNC) {
 		wpa_printf(MSG_INFO, "RADIUS: Possibly too long UDP frame for our buffer - dropping it");
 		return;
 	}