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Filename : secureio.py
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# coding=utf-8

# Copyright © Cloud Linux GmbH & Cloud Linux Software, Inc 2010-2018 All Rights Reserved
#
# Licensed under CLOUD LINUX LICENSE AGREEMENT
# http://cloudlinux.com/docs/LICENSE.TXT

# This module provides functions for secure I/O and filesystem operations

from __future__ import print_function
from __future__ import absolute_import
from __future__ import division
import grp
import sys
import tempfile
import contextlib
from clcommon import ClPwd
from clcommon.clpwd import drop_user_privileges

import os
from ctypes import (cdll, c_long, Structure, c_ushort, c_ubyte, c_char, POINTER,
                    c_int, c_void_p, c_char_p)

libc = cdll.LoadLibrary("libc.so.6")
try:
    liblve = cdll.LoadLibrary("libsecureio.so.0")
except OSError:
    liblve = cdll.LoadLibrary("liblve.so.0")
# --- libc functions -----------------------------------------------

ino_t = c_long
off_t = c_long


class DIRENTRY(Structure):
    _fields_ = [
        ('d_ino', ino_t),  # inode number
        ('d_off', off_t),  # offset to the next dirent
        ('d_reclen', c_ushort),  # length of this record
        ('d_type', c_ubyte),  # type of file; not supported by all file system types
        ('d_name', c_char * 256),  # filename
    ]


DIRENTRY_P = POINTER(DIRENTRY)

fchown = libc.fchown
fchown.argtypes = [c_int, c_int, c_int]
fchown.restype = c_int

fchmod = libc.fchmod
fchmod.argtypes = [c_int, c_int]
fchmod.restype = c_int

fdopendir = libc.fdopendir
# accepts file/dir descriptor (integer)
fdopendir.argtypes = [c_int]
# returns pointer to DIR structure
fdopendir.restype = c_void_p

readdir = libc.readdir
# accepts pointer to DIR structure
readdir.argtypes = [c_void_p]
# returns pointer to DIRENTRY structure
readdir.restype = DIRENTRY_P

rewinddir = libc.rewinddir
# accepts pointer to DIR structure
rewinddir.argtypes = [c_void_p]
# returns void
rewinddir.restype = None

closedir = libc.closedir
# accepts pointer to DIR structure
closedir.argtypes = [c_void_p]
closedir.restype = c_int


# --- liblve functions -----------------------------------------------

# Opens path for reading not following symlinks and verifies that opened path is inside parent_path
# Returns:
# descriptor if successful
# -1 if path does not exist or is a symlink
# -2 if opened path is NOT inside parent_path or cannot be determined
# accepts path, parent_path
_open_not_symlink = liblve.open_not_symlink
_open_not_symlink.argtypes = [c_char_p, c_char_p]
_open_not_symlink.restype = c_int

# Closes descriptor (if it is not equal -1)
# accepts file/dir descriptor (integer)
liblve.closefd.argtypes = [c_int]
# returns void
liblve.closefd.restype = None

# Tries to read first directory entry in order to ensure that descriptor is valid
# Returns 0 if reading succeeded or -1 if error has occured
check_dir = liblve.check_dir
# accepts descriptor
check_dir.argtypes = [c_int]
check_dir.restype = c_int

# Checks if path is a directory (in secure manner)
# Also opens path (if descriptor fd == -1) and then checks that opened path is inside parent_path
# Returns descriptor if path refers to directory
# Returns -1 if path does not exist or is not a directory
# Returns -2 if opened path is NOT inside parent_path or cannot be determined
isdir = liblve.isdir
# accepts path, descriptor, parent_path
isdir.argtypes = [c_char_p, c_int, c_char_p]
isdir.restype = c_int

# Sets permissions to directory (in secure manner)
# Returns descriptor if successful
# Returns -1 if error has occured
# Returns -2 if opened path is NOT inside parent_path or cannot be determined
# accepts: const char *path, mode_t perm, int fd, const char *parent_path
liblve.set_perm_dir_secure.argtypes = [c_char_p, c_int, c_int, c_char_p]
liblve.set_perm_dir_secure.restype = c_int

# Sets owner and group of directory (in secure manner)
# Returns descriptor if successful
# Returns -1 if error has occured
# Returns -2 if opened path is NOT inside parent_path or cannot be determined
# accepts: const char *path, uid_t uid, gid_t gid, int fd, const char *parent_path
liblve.set_owner_dir_secure.argtypes = [c_char_p, c_int, c_int, c_int, c_char_p]
liblve.set_owner_dir_secure.restype = c_int

# Creates directory if it does not exist, sets permissions/owner otherwise
# Returns descriptor if successful
# Returns -1 if error has occured
# accepts: const char *path, mode_t perm, uid_t uid, gid_t gid, int fd, const char *parent_path
liblve.create_dir_secure.argtypes = [c_char_p, c_int, c_int, c_int, c_int, c_char_p]
liblve.create_dir_secure.restype = c_int

# Recursive directory creation function
# Returns 0 if successful
# Returns -1 if error has occured
# accepts: const char *path, mode_t perm, uid_t uid, gid_t gid, const char *parent_path
liblve.makedirs_secure.argtypes = [c_char_p, c_int, c_int, c_int, c_char_p]
liblve.makedirs_secure.restype = c_int

# Writes absolute path pointed by descriptor fd to buffer *buf
# Returns buf if successful
# Returns NULL if error has occured
get_path_from_descriptor = liblve.get_path_from_descriptor
get_path_from_descriptor.argtypes = [c_int, c_char_p]
get_path_from_descriptor.restype = c_char_p

# Returns 1 if subdir is subdirectory of dir, 0 otherwise
is_subdir = liblve.is_subdir
is_subdir.argtypes = [c_char_p, c_char_p]
is_subdir.restype = c_int

# True :  euid/egid == 0/0
# False : euid/egid == user/user
# set by set_user_perm() and set_root_perm() functions
root_flag = True

LOGFILE = "/var/log/cagefs-update.log"

MIN_UID = 500

SILENT_FLAG = False


def open_not_symlink(path):
    return os.open(path, os.O_RDONLY | os.O_NOFOLLOW)


def open_file_not_symlink(path):
    return os.fdopen(open_not_symlink(path), 'r')


def flistdir(fd):
    """Returns list of entries of directory pointed by descriptor"""
    # Duplicate descriptor, because closedir() closes descriptor associated with directory stream
    fd2 = os.dup(fd)

    # Open directory stream
    dirp = fdopendir(fd2)
    if not dirp:
        raise Exception("fdopendir error")

    # Reset position of directory stream
    # (so it will be possible to read content of directory multiple times
    # via other descriptors that refer to the directory)
    rewinddir(dirp)

    dirlist = []
    while True:
        entryp = readdir(dirp)
        if not entryp:
            break
        entry = entryp.contents
        dirlist.append(entry.d_name)

    rewinddir(dirp)
    closedir(dirp)
    return dirlist


def closefd(fd):
    if fd is not None:
        try:
            os.close(fd)
        except OSError:
            pass


def set_perm_dir_secure(path, perm, parent_path, fd=None, logger=None):
    """Sets permissions to directory (in secure manner)
    Returns descriptor if successful
    Returns None if error has occured"""
    if fd is None:
        fd = -1
    fd = liblve.set_perm_dir_secure(path.encode(), perm, fd, parent_path.encode())
    if fd > 0:
        return fd
    if logger is not None:
        logger('Error: failed to set permissions of directory ' + path, False, True)
    return None


def set_owner_dir_secure(path, uid, gid, parent_path, fd=None, logger=None):
    """Sets owner and group of directory (in secure manner)
    Returns descriptor if successful
    Returns None if error has occured"""
    if fd is None:
        fd = -1
    fd = liblve.set_owner_dir_secure(path.encode(), uid, gid, fd, parent_path.encode())
    if fd > 0:
        return fd
    if logger is not None:
        logger('Error: failed to set owner of directory ' + path, False, True)
    return None


def create_dir_secure(path, perm, uid, gid, parent_path, fd=None, logger=None):
    """Creates directory if it does not exist, sets permissions/owner otherwise
    Returns descriptor if successful
    Returns None if error has occured"""
    if fd is None:
        fd = -1
    fd = liblve.create_dir_secure(path.encode(), perm, uid, gid, fd, parent_path.encode())
    if fd > 0:
        return fd
    if logger is not None:
        logger('Error : failed to create directory ' + path, False, True)
    return None


def makedirs_secure(path, perm, uid, gid, parent_path, logger=None):
    """Recursive directory creation function
    Returns 0 if successful
    Returns -1 if error has occured"""
    res = liblve.makedirs_secure(path.encode(), perm, uid, gid, parent_path.encode())
    if res and logger:
        logger('Error : failed to create directory ' + path, False, True)
    return res


def read_file_secure(filename, uid=None, gid=None, exit_on_error=True, write_log=True):
    """read file not following symlinks"""
    if (uid is None and not gid is None) or (not uid is None and gid is None):
        raise Exception("read_file_secure: uid and gid should be both null or be both not null")

    drop_perm = (uid is not None) and (gid is not None)
    if drop_perm:
        set_user_perm(uid, gid)

    try:
        file_object = open_file_not_symlink(filename)
        content = file_object.readlines()
        file_object.close()
        if drop_perm:
            set_root_perm()
        return content
    except (OSError, IOError) as e:
        if drop_perm:
            set_root_perm()
        logging('Error: failed to read ' + filename + ' : ' + str(e), SILENT_FLAG, 1, write_log)
        if not exit_on_error:
            raise
        sys.exit(1)


def write_file_secure(content, ini_path, uid, gid, drop_perm=True, perm=0o644, write_log=True):
    """Returns True if error has occured"""
    dirpath = os.path.dirname(ini_path)

    if drop_perm:
        set_user_perm(uid, gid)

    try:
        fd, temp_path = tempfile.mkstemp(prefix='cagefs_', dir=dirpath)
        file_object = os.fdopen(fd, 'w')
        file_object.write(''.join(content))
        if not drop_perm and uid is not None and gid is not None:
            if fchown(fd, uid, gid):
                raise OSError('fchown failed')
        if fchmod(fd, perm):
            raise OSError('fchmod failed')
        file_object.close()
    except (IOError, OSError) as e:
        try:
            file_object.close()
        except:
            pass
        try:
            os.close(fd)
        except:
            pass
        try:
            os.unlink(temp_path)
        except:
            pass
        if drop_perm:
            set_root_perm()
        logging('Error : failed to write file ' + ini_path + ' : ' + str(e).replace('Errno', 'Err code'), SILENT_FLAG, True, write_log)
        return True
    except Exception as e:
        logging('Error: ' + str(e), SILENT_FLAG, 1)
        sys.exit(1)

    error = False
    try:
        os.rename(temp_path, ini_path)
    except OSError as e:
        error = True
        logging('Error: failed to rename tempfile to ' + ini_path + ' : ' + str(e), SILENT_FLAG, 1, write_log)
        try:
            os.unlink(temp_path)
        except OSError:
            pass

    if drop_perm:
        set_root_perm()

    return error


def write_file_via_tempfile(
        content, dest_path, perm, prefix='', suffix='', as_user=None):
    """
    Safely write string content to a file
    :param content: str
    :param dest_path: str -> path to a file
    :param perm: int -> permissions for the file
    :param prefix: str -> add to temporary file name
    :param suffix: str -> add to temporary file name
    :param as_user: str -> name of the user to drop privileges to
    """
    if as_user is not None:
        old_groups = os.getgroups()
        drop_user_privileges(as_user, effective_or_real=True, set_env=False)

    dirpath = os.path.dirname(dest_path)
    fd, temp_path = None, None
    try:
        fd, temp_path = tempfile.mkstemp(
                prefix=prefix, suffix=suffix, dir=dirpath)
        with os.fdopen(fd, 'w', errors='surrogateescape') as f_temp:
            f_temp.write(content)
    except (IOError, OSError):
        if fd is None or temp_path is None:
            raise
        try:
            os.close(fd)
        except (IOError, OSError):
            pass
        try:
            os.unlink(temp_path)
        except (IOError, OSError):
            pass
        raise

    try:
        os.chmod(temp_path, perm)
        os.rename(temp_path, dest_path)
    except (OSError, IOError, TypeError):
        try:
            os.unlink(temp_path)
        except (OSError, IOError):
            pass
        raise

    if as_user is not None:
        ruid = os.getuid()
        os.seteuid(ruid)
        os.setegid(os.getgid())
        # All of the above can be called from user named as_user
        if ruid == 0:
            os.setgroups(old_groups)


def set_user_perm(uid, gid, exit=True):
    global root_flag

    try:
        os.setegid(gid)
    except (OSError,) as e:
        if exit:
            print_error('failed to set egid to ' + str(gid) + ': ' + str(e))
            sys.exit(1)
        else:
            return -1

    groups = get_groups(uid, gid)
    try:
        os.setgroups(groups)
    except (OSError,) as e:
        if exit:
            print_error('failed to set supplementary groups to :', groups, str(e))
            sys.exit(1)
        else:
            return -1

    try:
        os.seteuid(uid)
    except (OSError,) as e:
        if exit:
            print_error('failed to set euid to ' + str(uid) + ': ' + str(e))
            sys.exit(1)
        else:
            return -1

    if uid == 0:
        root_flag = True
    else:
        # If it's possible, switch on CAP_SYS_RESOURCE
        liblve.enable_quota_capability()
        root_flag = False


def set_root_perm(exit=True):
    global root_flag

    try:
        os.seteuid(0)
    except (OSError,) as e:
        if exit:
            print_error('failed to set euid to 0 :', str(e))
            sys.exit(1)
        else:
            return -1

    try:
        os.setegid(0)
    except (OSError,) as e:
        if exit:
            print_error('Error: failed to set egid to 0 :', str(e))
            sys.exit(1)
        else:
            return -1

    groups = get_groups(0, 0)
    try:
        os.setgroups(groups)
    except (OSError,) as e:
        if exit:
            print_error('Error: failed to set supplementary groups to :', groups, str(e))
            sys.exit(1)
        else:
            return -1

    root_flag = True


def print_error(*args):
    print("Error:", end=' ', file=sys.stderr)
    for a in args:
        print(a, end=' ', file=sys.stderr)
    print(file=sys.stderr)


def get_groups(uid, gid):
    """Returns supplementary groups for uid"""
    gr = get_grp_dict()
    pw = get_pwd_dict()
    groups = set()
    for group in gr:
        members = gr[group].gr_mem
        for user in members:
            try:
                member_uid = pw[user].pw_uid
            except KeyError:
                continue
            if member_uid == uid:
                groups.add(gr[group].gr_gid)
    groups.add(gid)
    return list(groups)

grp_dict = None


def get_grp_dict():
    global grp_dict
    if grp_dict is None:
        grp_dict = {}
        gr = grp.getgrall()
        for line in gr:
            grp_dict[line.gr_name] = line
    return grp_dict


clpwd = ClPwd(min_uid=MIN_UID)


def get_pwd_dict():
    return clpwd.get_user_dict()



log_file = None

def logging(msg, silent=False, verbose=True, write_log=True):
    global log_file
    if not silent:
        if verbose:
            print(msg)

    if write_log:
        root_flag_saved = root_flag
        if not root_flag:
            uid, gid = get_perm()
            set_root_perm()
        try:
            if log_file is None:
                umask_saved = os.umask(0o22)
                # log_file is opened in "line buffered" mode
                log_file = open(LOGFILE, 'w', 1)
                os.umask(umask_saved)
            log_file.write(msg)
            log_file.write("\n")
        except (OSError, IOError) as e:
            print_error("writing to ", LOGFILE, str(e))
            sys.exit(1)
        if not root_flag_saved:
            set_user_perm(uid, gid)


def get_perm():
    try:
        uid = os.geteuid()
        gid = os.getegid()
    except (OSError,) as e:
        print_error('failed to get (euid,egid)', str(e))
        sys.exit(1)
    return uid, gid


def set_capability(clear=False):
    """
    Set CAP_SYS_RESOURCE capability

    :param bool clear: Set on if it's true, set off otherwise
    :return: 0 for success, -1 otherwise
    :rtype: int
    """
    return liblve.disable_quota_capability() if clear \
        else liblve.enable_quota_capability()


def change_uid(uid):
    """
    Change effective uid of current process and set CAP_SYS_RESOURCE capbality
    to prevent "Disk quota exceeded" error

    :param int euid: User ID to set it as current effective UID
    :return: 0 if capability was set successfuly, -1 otherwise
    :rtype: int
    """
    os.seteuid(uid)
    return set_capability()


def _set_quota_checks_status(enabled):
    """
    Disable quota kernel check to allow us to write
    more than user can by quota.
    """
    if not enabled:
        liblve.enable_quota_capability()
    else:
        liblve.disable_quota_capability()


@contextlib.contextmanager
def disable_quota():
    _set_quota_checks_status(enabled=False)
    try:
        yield
    finally:
        _set_quota_checks_status(enabled=True)


@contextlib.contextmanager
def set_umask(umask_value):
    saved_umask = os.umask(umask_value)
    try:
        yield
    finally:
        os.umask(saved_umask)