From 72abb9e2756d5c19f43c7f3d83f3d8eade510ede Mon Sep 17 00:00:00 2001
From: jjungo <j.jungo@gmail.com>
Date: Fri, 18 Dec 2015 12:43:47 +0100
Subject: [PATCH] Fix #12 Segmentation fault

Problem: bad parsing argument
Solution:
    * check the number of arguments
    * first argument is "-s" or "-c"

This commit doesn't check if IPv4 is valid.
---
 icmptunnel.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/icmptunnel.c b/icmptunnel.c
index e6c7d0e..526c044 100644
--- a/icmptunnel.c
+++ b/icmptunnel.c
@@ -8,14 +8,34 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#define ARG_SERVER_MODE "-s"
+#define ARG_CLIENT_MODE "-c"
+
+void usage()
+{
+  printf("Wrong argument\n");
+  fprintf(stdout, "usage: icmptunnel [-s serverip] | [-c clientip]\n");
+}
+
 int main(int argc, char *argv[])
 {
   char ip_addr[100] = {0,};
-  if ((strlen(argv[2]) + 1) > sizeof(ip_addr)){
-      perror("Bad ip argument\n");
-      exit(EXIT_FAILURE);
+  if ((argc < 3) || ((strlen(argv[2]) + 1) > sizeof(ip_addr))) {
+    usage();
+    exit(EXIT_FAILURE);
   }
   memcpy(ip_addr, argv[2], strlen(argv[2]) + 1);
-  run_tunnel(ip_addr, !strcmp(argv[1], "-s"));
+
+  if (strncmp(argv[1], ARG_SERVER_MODE, strlen(argv[1])) == 0) {
+    run_tunnel(ip_addr, 1);
+  }
+  else if (strncmp(argv[1], ARG_CLIENT_MODE, strlen(argv[1])) == 0) {
+    run_tunnel(ip_addr, 0);
+  }
+  else {
+    usage();
+    exit(EXIT_FAILURE);
+  }
+
   return EXIT_SUCCESS;
 }