#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <sys/wait.h>
#include <sys/vfs.h>
#include <sys/statvfs.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <grp.h>
#include <stdbool.h>
#include <stdarg.h>
#ifndef CLONE_NEWNS
# define CLONE_NEWNS 0x00020000
#endif
#ifndef CLONE_NEWUTS
# define CLONE_NEWUTS 0x04000000
#endif
#ifndef CLONE_NEWIPC
# define CLONE_NEWIPC 0x08000000
#endif
#ifndef CLONE_NEWNET
# define CLONE_NEWNET 0x40000000
#endif
#ifndef CLONE_NEWUSER
# define CLONE_NEWUSER 0x10000000
#endif
#ifndef CLONE_NEWPID
# define CLONE_NEWPID 0x20000000
#endif
#ifndef MS_REC
# define MS_REC 16384
#endif
#ifndef MS_RELATIME
# define MS_RELATIME (1 << 21)
#endif
#ifndef MS_STRICTATIME
# define MS_STRICTATIME (1 << 24)
#endif
static void die(char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vfprintf(stderr, fmt, ap);
va_end(ap);
exit(EXIT_FAILURE);
}
static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt, va_list ap)
{
char buf[4096];
int fd;
ssize_t written;
int buf_len;
buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
if (buf_len < 0) {
die("vsnprintf failed: %s\n",
strerror(errno));
}
if (buf_len >= sizeof(buf)) {
die("vsnprintf output truncated\n");
}
fd = open(filename, O_WRONLY);
if (fd < 0) {
if ((errno == ENOENT) && enoent_ok)
return;
die("open of %s failed: %s\n",
filename, strerror(errno));
}
written = write(fd, buf, buf_len);
if (written != buf_len) {
if (written >= 0) {
die("short write to %s\n", filename);
} else {
die("write to %s failed: %s\n",
filename, strerror(errno));
}
}
if (close(fd) != 0) {
die("close of %s failed: %s\n",
filename, strerror(errno));
}
}
static void maybe_write_file(char *filename, char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vmaybe_write_file(true, filename, fmt, ap);
va_end(ap);
}
static void write_file(char *filename, char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vmaybe_write_file(false, filename, fmt, ap);
va_end(ap);
}
static int read_mnt_flags(const char *path)
{
int ret;
struct statvfs stat;
int mnt_flags;
ret = statvfs(path, &stat);
if (ret != 0) {
die("statvfs of %s failed: %s\n",
path, strerror(errno));
}
if (stat.f_flag & ~(ST_RDONLY | ST_NOSUID | ST_NODEV | \
ST_NOEXEC | ST_NOATIME | ST_NODIRATIME | ST_RELATIME | \
ST_SYNCHRONOUS | ST_MANDLOCK)) {
die("Unrecognized mount flags\n");
}
mnt_flags = 0;
if (stat.f_flag & ST_RDONLY)
mnt_flags |= MS_RDONLY;
if (stat.f_flag & ST_NOSUID)
mnt_flags |= MS_NOSUID;
if (stat.f_flag & ST_NODEV)
mnt_flags |= MS_NODEV;
if (stat.f_flag & ST_NOEXEC)
mnt_flags |= MS_NOEXEC;
if (stat.f_flag & ST_NOATIME)
mnt_flags |= MS_NOATIME;
if (stat.f_flag & ST_NODIRATIME)
mnt_flags |= MS_NODIRATIME;
if (stat.f_flag & ST_RELATIME)
mnt_flags |= MS_RELATIME;
if (stat.f_flag & ST_SYNCHRONOUS)
mnt_flags |= MS_SYNCHRONOUS;
if (stat.f_flag & ST_MANDLOCK)
mnt_flags |= ST_MANDLOCK;
return mnt_flags;
}
static void create_and_enter_userns(void)
{
uid_t uid;
gid_t gid;
uid = getuid();
gid = getgid();
if (unshare(CLONE_NEWUSER) !=0) {
die("unshare(CLONE_NEWUSER) failed: %s\n",
strerror(errno));
}
maybe_write_file("/proc/self/setgroups", "deny");
write_file("/proc/self/uid_map", "0 %d 1", uid);
write_file("/proc/self/gid_map", "0 %d 1", gid);
if (setgid(0) != 0) {
die ("setgid(0) failed %s\n",
strerror(errno));
}
if (setuid(0) != 0) {
die("setuid(0) failed %s\n",
strerror(errno));
}
}
static
bool test_unpriv_remount(const char *fstype, const char *mount_options,
int mount_flags, int remount_flags, int invalid_flags)
{
pid_t child;
child = fork();
if (child == -1) {
die("fork failed: %s\n",
strerror(errno));
}
if (child != 0) {
pid_t pid;
int status;
pid = waitpid(child, &status, 0);
if (pid == -1) {
die("waitpid failed: %s\n",
strerror(errno));
}
if (pid != child) {
die("waited for %d got %d\n",
child, pid);
}
if (!WIFEXITED(status)) {
die("child did not terminate cleanly\n");
}
return WEXITSTATUS(status) == EXIT_SUCCESS;
}
create_and_enter_userns();
if (unshare(CLONE_NEWNS) != 0) {
die("unshare(CLONE_NEWNS) failed: %s\n",
strerror(errno));
}
if (mount("testing", "/tmp", fstype, mount_flags, mount_options) != 0) {
die("mount of %s with options '%s' on /tmp failed: %s\n",
fstype,
mount_options? mount_options : "",
strerror(errno));
}
create_and_enter_userns();
if (unshare(CLONE_NEWNS) != 0) {
die("unshare(CLONE_NEWNS) failed: %s\n",
strerror(errno));
}
if (mount("/tmp", "/tmp", "none",
MS_REMOUNT | MS_BIND | remount_flags, NULL) != 0) {
die("remount of /tmp failed: %s\n",
strerror(errno));
}
if (mount("/tmp", "/tmp", "none",
MS_REMOUNT | MS_BIND | invalid_flags, NULL) == 0) {
die("remount of /tmp with invalid flags "
"succeeded unexpectedly\n");
}
exit(EXIT_SUCCESS);
}
static bool test_unpriv_remount_simple(int mount_flags)
{
return test_unpriv_remount("ramfs", NULL, mount_flags, mount_flags, 0);
}
static bool test_unpriv_remount_atime(int mount_flags, int invalid_flags)
{
return test_unpriv_remount("ramfs", NULL, mount_flags, mount_flags,
invalid_flags);
}
static bool test_priv_mount_unpriv_remount(void)
{
pid_t child;
int ret;
const char *orig_path = "/dev";
const char *dest_path = "/tmp";
int orig_mnt_flags, remount_mnt_flags;
child = fork();
if (child == -1) {
die("fork failed: %s\n",
strerror(errno));
}
if (child != 0) {
pid_t pid;
int status;
pid = waitpid(child, &status, 0);
if (pid == -1) {
die("waitpid failed: %s\n",
strerror(errno));
}
if (pid != child) {
die("waited for %d got %d\n",
child, pid);
}
if (!WIFEXITED(status)) {
die("child did not terminate cleanly\n");
}
return WEXITSTATUS(status) == EXIT_SUCCESS;
}
orig_mnt_flags = read_mnt_flags(orig_path);
create_and_enter_userns();
ret = unshare(CLONE_NEWNS);
if (ret != 0) {
die("unshare(CLONE_NEWNS) failed: %s\n",
strerror(errno));
}
ret = mount(orig_path, dest_path, "bind", MS_BIND | MS_REC, NULL);
if (ret != 0) {
die("recursive bind mount of %s onto %s failed: %s\n",
orig_path, dest_path, strerror(errno));
}
ret = mount(dest_path, dest_path, "none",
MS_REMOUNT | MS_BIND | orig_mnt_flags , NULL);
if (ret != 0) {
die("remount of /tmp failed: %s\n",
strerror(errno));
}
remount_mnt_flags = read_mnt_flags(dest_path);
if (orig_mnt_flags != remount_mnt_flags) {
die("Mount flags unexpectedly changed during remount of %s originally mounted on %s\n",
dest_path, orig_path);
}
exit(EXIT_SUCCESS);
}
int main(int argc, char **argv)
{
if (!test_unpriv_remount_simple(MS_RDONLY)) {
die("MS_RDONLY malfunctions\n");
}
if (!test_unpriv_remount("devpts", "newinstance", MS_NODEV, MS_NODEV, 0)) {
die("MS_NODEV malfunctions\n");
}
if (!test_unpriv_remount_simple(MS_NOSUID)) {
die("MS_NOSUID malfunctions\n");
}
if (!test_unpriv_remount_simple(MS_NOEXEC)) {
die("MS_NOEXEC malfunctions\n");
}
if (!test_unpriv_remount_atime(MS_RELATIME,
MS_NOATIME))
{
die("MS_RELATIME malfunctions\n");
}
if (!test_unpriv_remount_atime(MS_STRICTATIME,
MS_NOATIME))
{
die("MS_STRICTATIME malfunctions\n");
}
if (!test_unpriv_remount_atime(MS_NOATIME,
MS_STRICTATIME))
{
die("MS_NOATIME malfunctions\n");
}
if (!test_unpriv_remount_atime(MS_RELATIME|MS_NODIRATIME,
MS_NOATIME))
{
die("MS_RELATIME|MS_NODIRATIME malfunctions\n");
}
if (!test_unpriv_remount_atime(MS_STRICTATIME|MS_NODIRATIME,
MS_NOATIME))
{
die("MS_STRICTATIME|MS_NODIRATIME malfunctions\n");
}
if (!test_unpriv_remount_atime(MS_NOATIME|MS_NODIRATIME,
MS_STRICTATIME))
{
die("MS_NOATIME|MS_DIRATIME malfunctions\n");
}
if (!test_unpriv_remount("ramfs", NULL, MS_STRICTATIME, 0, MS_NOATIME))
{
die("Default atime malfunctions\n");
}
if (!test_priv_mount_unpriv_remount()) {
die("Mount flags unexpectedly changed after remount\n");
}
return EXIT_SUCCESS;
}
