linux.py

import ctypes
import ctypes.util
import os
from pathlib import Path
from typing import Union


libc = ctypes.CDLL(ctypes.util.find_library('c'), use_errno=True)
libc.mount.argtypes = (ctypes.c_char_p, ctypes.c_char_p, ctypes.c_char_p, ctypes.c_ulong, ctypes.c_char_p)
libc.mount.restype = ctypes.c_int
libc.umount.argtypes = (ctypes.c_char_p, )
libc.umount.restype = ctypes.c_int
libc.unshare.argtypes = (ctypes.c_int, )
libc.unshare.restype = ctypes.c_int


CLONE_NEWNET = 0x40000000
CLONE_NEWPID = 0x20000000
CLONE_NEWUSER = 0x10000000
CLONE_NEWIPC = 0x8000000
CLONE_NEWUTS = 0x4000000
CLONE_NEWNS = 0x20000


MS_RDONLY = 0x1
MS_NOSUID = 0x2
MS_NODEV = 0x4
MS_NOEXEC = 0x8
MS_SYNCHRONOUS = 0x10
MS_REMOUNT = 0x20
MS_MANDLOCK = 0x40
MS_DIRSYNC = 0x80
MS_NOATIME = 0x400
MS_NODIRATIME = 0x800
MS_BIND = 0x1000
MS_MOVE = 0x2000
MS_REC = 0x4000
MS_SILENT = 0x8000
MS_UNBINDABLE = 0x20000
MS_PRIVATE = 0x40000
MS_SLAVE = 0x80000
MS_SHARED = 0x100000
MS_RELATIME = 0x200000
MS_STRICTATIME = 0x1000000
MS_LAZYTIME = 0x2000000


def mount(source: Union[str, Path], target: Union[str, Path], fs_type: str, flags: int = 0, options: str = ''):
    ret = libc.mount(str(source).encode(), str(target).encode(), fs_type.encode(), flags, options.encode())
    if ret == -1:
        errno = ctypes.get_errno()
        raise OSError(errno, f'Fail to mount {source} ({fs_type}) on {target} with "{options}": {os.strerror(errno)}')


def umount(target: Union[str, Path]):
    ret = libc.umount(str(target).encode())
    if ret == -1:
        errno = ctypes.get_errno()
        raise OSError(errno, f'Fail to umount {target}: {os.strerror(errno)}')


def unshare(flags: int):
    ret = libc.unshare(flags)
    if ret == -1:
        errno = ctypes.get_errno()
        raise OSError(errno, f'Fail to unshare with flags {flags:#x}: {os.strerror(errno)}')


def want_to_mount_like_root():
    uid, gid = os.geteuid(), os.getegid()
    assert uid != 0 and gid != 0  # already have root privileges
    unshare(CLONE_NEWUSER | CLONE_NEWNS)
    Path('/proc/self/uid_map').write_text(f'0 {uid} 1')
    Path('/proc/self/setgroups').write_text('deny')
    Path('/proc/self/gid_map').write_text(f'0 {gid} 1')