map: fix psidlen becoming negative (FS#1430)

Fix psidlen becomes negative in case embedded address bit lenght is smaller than
IPv4 suffix length.
While at it improve parameter checking making the code more logical and
easier to read.

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>

package/network/ipv6/map/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=map
 PKG_VERSION:=4
-PKG_RELEASE:=9
+PKG_RELEASE:=10
 PKG_LICENSE:=GPL-2.0
 
 include $(INCLUDE_DIR)/package.mk

package/network/ipv6/map/src/mapcalc.c

@@ -4,6 +4,7 @@
  * Author: Steven Barth <cyrus@openwrt.org>
  * Copyright (c) 2014-2015 cisco Systems, Inc.
  * Copyright (c) 2015 Steven Barth <cyrus@openwrt.org>
+ * Copyright (c) 2018 Hans Dedecker <dedeckeh@gmail.com>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2
@@ -311,25 +312,30 @@ int main(int argc, char *argv[])
 
 		if (psidlen <= 0) {
 			psidlen = ealen - (32 - prefix4len);
+			if (psidlen < 0)
+				psidlen = 0;
+
 			psid = -1;
 		}
 
-		if (psid < 0 && psidlen <= 16 && psidlen >= 0 && pdlen >= 0 && ealen >= psidlen) {
+		if (prefix4len < 0 || prefix6len < 0 || ealen < 0 || psidlen > 16 || ealen < psidlen) {
+			fprintf(stderr, "Skipping invalid or incomplete rule: %s\n", argv[i]);
+			status = 1;
+			continue;
+		}
+
+		if (psid < 0 && psidlen >= 0 && pdlen >= 0) {
 			bmemcpys64(&psid16, &pd, prefix6len + ealen - psidlen, psidlen);
 			psid = be16_to_cpu(psid16);
 		}
 
-		psid = psid >> (16 - psidlen);
-		psid16 = cpu_to_be16(psid);
-		psid = psid << (16 - psidlen);
-
-		if (prefix4len < 0 || prefix6len < 0 || ealen < 0 || ealen < psidlen) {
-			fprintf(stderr, "Skipping invalid or incomplete rule: %s\n", argv[i]);
-			status = 1;
-			continue;
+		if (psidlen > 0) {
+			psid = psid >> (16 - psidlen);
+			psid16 = cpu_to_be16(psid);
+			psid = psid << (16 - psidlen);
 		}
 
-		if ((pdlen >= 0 || ealen == psidlen) && ealen >= psidlen) {
+		if (pdlen >= 0 || ealen == psidlen) {
 			bmemcpys64(&ipv4addr, &pd, prefix6len, ealen - psidlen);
 			ipv4addr.s_addr = htonl(ntohl(ipv4addr.s_addr) >> prefix4len);
 			bmemcpy(&ipv4addr, &ipv4prefix, prefix4len);