my attempt at level0 on vortex wargame at www.overthewire.org

level0.c

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <byteswap.h>

/* TODO:
   * replace static return codes with constants
   * factor helper functions into separate companion library
   * replace reliance on __builtin_bswap32 with more portable function
*/

/* prototypes for socket helper functions */
int senddata (int sockfd, const void *msg, int len);
int recvdata (int sockfd, void *buf, int len);

int main (int argc, char **argv) {
   int status, sockfd;
   unsigned int sum, buf[4], i;
   char ip[INET_ADDRSTRLEN], credsbuf[1024];
   struct addrinfo hints, *servinfo, *p;

   memset(&hints, 0, sizeof hints);
   memset(credsbuf, 0, sizeof credsbuf);
   hints.ai_family = AF_UNSPEC;
   hints.ai_socktype = SOCK_STREAM;

   if ((status = getaddrinfo("vortex.labs.overthewire.org", "5842", &hints, &servinfo)) != 0) {
      fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
      exit(1);
   }

   for (p = servinfo; p != NULL; p = p->ai_next) {

      inet_ntop(AF_INET, ((struct sockaddr_in *) p->ai_addr)->sin_addr, ip, INET_ADDRSTRLEN);
      printf("Connecting to %s ...\n",ip); 

      if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) {
         perror("socket");
         continue;
      }

      if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
         close(sockfd);
         perror("connect");
         continue;
      }

      break;
   }

   if (p == NULL) {
      fprintf(stderr, "failed to connect\n");
      exit(2);
   }

   printf("success.  reading 4 unsigned integers\n");

   for (i=0; i < 4; i++) {
      recvdata(sockfd, buf + i, sizeof buf[i]);
      buf[i] = __builtin_bswap32(buf[i]);
   }

   printf("The numbers returned were: %u\t%u\t%u\t%u\n", buf[0], buf[1], buf[2], buf[3]);

   sum = __builtin_bswap32(buf[0] + buf[1] + buf[2] + buf[3]);

   status = 0;

   printf("Sending sum of %u back\n", sum);

   do {
      status = senddata(sockfd, &sum + status, (sizeof sum) - status);
   } while (status < sizeof sum);
      

   printf("Receiving feedback:\n");

   recvdata(sockfd, credsbuf, sizeof credsbuf);

   printf("%s\n", credsbuf);
   freeaddrinfo(servinfo);
   return 0;
}

int senddata (int sockfd, const void *msg, int len) {
   int status;

   status = send(sockfd, msg, len, 0);

   if (status == -1) {
      fprintf(stderr, "send failed; %s\n", strerror(errno));
      exit(5);
   }

   return status;
}

int recvdata (int sockfd, void *buf, int len) {
   int status;

   status = recv(sockfd, buf, len, 0);

   if (status == -1 || status == 0) {
      fprintf(stderr, "recv failed; %s\n", strerror(errno));
      exit(errno);
   }

   /*
   if (status == 0) {
      fprintf(stderr, "connection closed by remote host\n");
      exit(4);
   }
   */

   return status;
}