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File name : fileutils.py
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'''Functions to manage apport problem report files.'''

# Copyright (C) 2006 - 2009 Canonical Ltd.
# Author: Martin Pitt <martin.pitt@ubuntu.com>
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2 of the License, or (at your
# option) any later version.  See http://www.gnu.org/copyleft/gpl.html for
# the full text of the license.

import os, glob, subprocess, os.path, time, pwd, sys, requests_unixsocket
import stat
from operator import itemgetter

try:
    from configparser import (ConfigParser, NoOptionError, NoSectionError,
                              MissingSectionHeaderError)
    (ConfigParser, NoOptionError, NoSectionError)  # pyflakes
except ImportError:
    # Python 2
    from ConfigParser import (ConfigParser, NoOptionError, NoSectionError,
                              MissingSectionHeaderError)

from problem_report import ProblemReport

from apport.packaging_impl import impl as packaging

report_dir = os.environ.get('APPORT_REPORT_DIR', '/var/crash')
core_dir = '/var/lib/apport/coredump'
max_corefiles_per_uid = 5

_config_file = '~/.config/apport/settings'


def allowed_to_report():
    '''Check whether crash reporting is enabled.'''

    if not os.access("/usr/bin/whoopsie", os.X_OK):
        return True

    try:
        return subprocess.call(["/bin/systemctl", "-q", "is-enabled", "whoopsie.service"]) == 0
    except OSError:
        return False


def get_dbus_socket(dbus_addr):
    '''Extract the socket from a DBus address.'''

    if not dbus_addr:
        return None

    # Only support unix domain sockets, and only the default Ubuntu path
    if not dbus_addr.startswith("unix:path=/run/user/"):
        return None

    # Prevent path traversal
    if "../" in dbus_addr:
        return None

    # Don't support escaped values, multiple addresses, or multiple keys
    # and values
    for search in ["%", ",", ";"]:
        if search in dbus_addr:
            return None

    parts = dbus_addr.split("=")
    if len(parts) != 2:
        return None

    return parts[1]


def find_package_desktopfile(package):
    '''Return a package's .desktop file.

    If given package is installed and has a single .desktop file, return the
    path to it, otherwise return None.
    '''
    if package is None:
        return None

    desktopfile = None

    for line in packaging.get_files(package):
        if line.endswith('.desktop'):
            # restrict to autostart and applications, see LP#1147528
            if not line.startswith('/etc/xdg/autostart') and not line.startswith('/usr/share/applications/'):
                continue

            if desktopfile:
                return None  # more than one
            else:
                # only consider visible ones
                with open(line, 'rb') as f:
                    if b'NoDisplay=true' not in f.read():
                        desktopfile = line

    return desktopfile


def likely_packaged(file):
    '''Check whether the given file is likely to belong to a package.

    This is semi-decidable: A return value of False is definitive, a True value
    is only a guess which needs to be checked with find_file_package().
    However, this function is very fast and does not access the package
    database.
    '''
    pkg_whitelist = ['/bin/', '/boot', '/etc/', '/initrd', '/lib', '/sbin/',
                     '/opt', '/usr/', '/var']  # packages only ship executables in these directories

    whitelist_match = False
    for i in pkg_whitelist:
        if file.startswith(i):
            whitelist_match = True
            break
    return whitelist_match and not file.startswith('/usr/local/') and not \
        file.startswith('/var/lib/')


def find_file_package(file):
    '''Return the package that ships the given file.

    Return None if no package ships it.
    '''
    # resolve symlinks in directories
    (dir, name) = os.path.split(file)
    resolved_dir = os.path.realpath(dir)
    if os.path.isdir(resolved_dir):
        file = os.path.join(resolved_dir, name)

    if not likely_packaged(file):
        return None

    return packaging.get_file_package(file)


def find_snap(snap):
    '''Return the data of the given snap.

    Return None if the snap is not found to be installed.
    '''
    session = requests_unixsocket.Session()
    try:
        r = session.get('http+unix://%2Frun%2Fsnapd.socket/v2/snaps/{}'.format(snap))
        if r.status_code == 200:
            j = r.json()
            return j["result"]
    except Exception:
        return None


def seen_report(report):
    '''Check whether the report file has already been processed earlier.'''

    st = os.stat(report)
    return (st.st_atime > st.st_mtime) or (st.st_size == 0)


def mark_report_upload(report):
    upload = '%s.upload' % report.rsplit('.', 1)[0]
    uploaded = '%s.uploaded' % report.rsplit('.', 1)[0]
    # if uploaded exists and is older than the report remove it and upload
    if os.path.exists(uploaded) and os.path.exists(upload):
        report_st = os.stat(report)
        upload_st = os.stat(upload)
        if upload_st.st_mtime < report_st.st_mtime:
            os.unlink(upload)
    with open(upload, 'a'):
        pass


def mark_hanging_process(report, pid):
    if 'ExecutablePath' in report:
        subject = report['ExecutablePath'].replace('/', '_')
    else:
        raise ValueError('report does not have the ExecutablePath attribute')

    uid = os.geteuid()
    base = '%s.%s.%s.hanging' % (subject, str(uid), pid)
    path = os.path.join(report_dir, base)
    with open(path, 'a'):
        pass


def mark_report_seen(report):
    '''Mark given report file as seen.'''

    st = os.stat(report)
    try:
        os.utime(report, (st.st_mtime, st.st_mtime - 1))
    except OSError:
        # file is probably not our's, so do it the slow and boring way
        # change the file's access time until it stat's different than the mtime.
        # This might take a while if we only have 1-second resolution. Time out
        # after 1.2 seconds.
        timeout = 12
        while timeout > 0:
            f = open(report)
            f.read(1)
            f.close()
            try:
                st = os.stat(report)
            except OSError:
                return

            if st.st_atime > st.st_mtime:
                break
            time.sleep(0.1)
            timeout -= 1

        if timeout == 0:
            # happens on noatime mounted partitions; just give up and delete
            delete_report(report)


def get_all_reports():
    '''Return a list with all report files accessible to the calling user.'''

    reports = []
    for r in glob.glob(os.path.join(report_dir, '*.crash')):
        try:
            if os.path.getsize(r) > 0 and os.access(r, os.R_OK | os.W_OK):
                reports.append(r)
        except OSError:
            # race condition, can happen if report disappears between glob and
            # stat
            pass
    return reports


def get_new_reports():
    '''Get new reports for calling user.

    Return a list with all report files which have not yet been processed
    and are accessible to the calling user.
    '''
    reports = []
    for r in get_all_reports():
        try:
            if not seen_report(r):
                reports.append(r)
        except OSError:
            # race condition, can happen if report disappears between glob and
            # stat
            pass
    return reports


def get_all_system_reports():
    '''Get all system reports.

    Return a list with all report files which belong to a system user (i. e.
    uid < 500 according to LSB).
    '''
    reports = []
    for r in glob.glob(os.path.join(report_dir, '*.crash')):
        try:
            st = os.stat(r)
            if st.st_size > 0 and st.st_uid < 500:
                # filter out guest session crashes; they might have a system UID
                try:
                    pw = pwd.getpwuid(st.st_uid)
                    if pw.pw_name.startswith('guest'):
                        continue
                except KeyError:
                    pass

                reports.append(r)
        except OSError:
            # race condition, can happen if report disappears between glob and
            # stat
            pass
    return reports


def get_new_system_reports():
    '''Get new system reports.

    Return a list with all report files which have not yet been processed
    and belong to a system user (i. e. uid < 500 according to LSB).
    '''
    return [r for r in get_all_system_reports() if not seen_report(r)]


def delete_report(report):
    '''Delete the given report file.

    If unlinking the file fails due to a permission error (if report_dir is not
    writable to normal users), the file will be truncated to 0 bytes instead.
    '''
    try:
        os.unlink(report)
    except OSError:
        with open(report, 'w') as f:
            f.truncate(0)


def get_recent_crashes(report):
    '''Return the number of recent crashes for the given report file.

    Return the number of recent crashes (currently, crashes which happened more
    than 24 hours ago are discarded).
    '''
    pr = ProblemReport()
    pr.load(report, False, key_filter=['CrashCounter', 'Date'])
    try:
        count = int(pr['CrashCounter'])
        report_time = time.mktime(time.strptime(pr['Date']))
        cur_time = time.mktime(time.localtime())
        # discard reports which are older than 24 hours
        if cur_time - report_time > 24 * 3600:
            return 0
        return count
    except (ValueError, KeyError):
        return 0


def make_report_file(report, uid=None):
    '''Construct a canonical pathname for a report and open it for writing

    If uid is not given, it defaults to the effective uid of the current process.
    The report file must not exist already, to prevent losing previous reports
    or symlink attacks.

    Return an open file object for binary writing.
    '''
    if 'ExecutablePath' in report:
        subject = report['ExecutablePath'].replace('/', '_')
    elif 'Package' in report:
        subject = report['Package'].split(None, 1)[0]
    else:
        raise ValueError('report has neither ExecutablePath nor Package attribute')

    if not uid:
        uid = os.geteuid()

    path = os.path.join(report_dir, '%s.%s.crash' % (subject, str(uid)))
    if sys.version >= '3':
        return open(path, 'xb')
    else:
        return os.fdopen(os.open(path, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o640), 'wb')


def check_files_md5(sumfile):
    '''Check file integrity against md5 sum file.

    sumfile must be md5sum(1) format (relative to /).

    Return a list of files that don't match.
    '''
    assert os.path.exists(sumfile)
    m = subprocess.Popen(['/usr/bin/md5sum', '-c', sumfile],
                         stdout=subprocess.PIPE, stderr=subprocess.PIPE,
                         cwd='/', env={})
    out = m.communicate()[0].decode()

    # if md5sum succeeded, don't bother parsing the output
    if m.returncode == 0:
        return []

    mismatches = []
    for line in out.splitlines():
        if line.endswith('FAILED'):
            mismatches.append(line.rsplit(':', 1)[0])

    return mismatches


def get_config(section, setting, default=None, path=None, bool=False):
    '''Return a setting from user configuration.

    This is read from ~/.config/apport/settings or path. If bool is True, the
    value is interpreted as a boolean.

    Privileges may need to be dropped before calling this.
    '''

    if not path:
        # Properly handle dropped privileges
        homedir = pwd.getpwuid(os.geteuid())[5]
        path = _config_file.replace("~", homedir)

    contents = ''
    fd = None
    f = None
    if not get_config.config:
        get_config.config = ConfigParser(interpolation=None)

        try:
            fd = os.open(path, os.O_NOFOLLOW | os.O_RDONLY)
            st = os.fstat(fd)
            if stat.S_ISREG(st.st_mode):
                f = os.fdopen(fd, 'r')
                # Limit size to prevent DoS
                contents = f.read(500)
        except (IOError, OSError):
            pass
        finally:
            if f is not None:
                f.close()
            elif fd is not None:
                os.close(fd)

    try:
        get_config.config.read_string(contents)
    except MissingSectionHeaderError:
        pass

    try:
        if bool:
            return get_config.config.getboolean(section, setting)
        else:
            return get_config.config.get(section, setting)
    except (NoOptionError, NoSectionError):
        return default


get_config.config = None


def get_starttime(contents):
    '''Extracts the starttime from the contents of a stat file'''

    # 22nd field in a stat file is the time the process started after
    # system boot in clock ticks. In order to prevent filename
    # manipulations including spaces or extra parentheses, skip all the way
    # to the very last closing parentheses, then start counting.
    stripped = contents[contents.rfind(")") + 2:]
    # We've skipped over the PID and the filename, so index is now 19.
    return int(stripped.split()[19])


def get_uid_and_gid(contents):
    '''Extracts the uid and gid from the contents of a status file'''

    real_uid = None
    real_gid = None
    for line in contents.splitlines():
        # Iterate through the whole contents to make sure we're getting
        # the last Uid and Gid lines in the file and not a manipulated
        # process name with embedded newlines.
        if line.startswith('Uid:') and len(line.split()) > 1:
            real_uid = int(line.split()[1])
        elif line.startswith('Gid:') and len(line.split()) > 1:
            real_gid = int(line.split()[1])
    return (real_uid, real_gid)


def search_map(mapfd, uid):
    '''Search for an ID in a map fd'''
    for line in mapfd:
        fields = line.split()
        if len(fields) != 3:
            continue

        host_start = int(fields[1])
        host_end = host_start + int(fields[2])

        if uid >= host_start and uid <= host_end:
            return True

    return False


def get_boot_id():
    '''Gets the kernel boot id'''

    with open('/proc/sys/kernel/random/boot_id') as f:
        boot_id = f.read().strip()
    return boot_id


def get_process_path(proc_pid_fd=None):
    '''Gets the process path from a proc directory file descriptor'''

    if proc_pid_fd is None:
        return 'unknown'
    try:
        return os.readlink('exe', dir_fd=proc_pid_fd)
    except OSError:
        return 'unknown'


def get_core_path(pid=None, exe=None, uid=None, timestamp=None, proc_pid_fd=None):
    '''Get the path to a core file'''

    if pid is None:
        pid = 'unknown'
        timestamp = 'unknown'
    else:
        if timestamp is None:
            with open("/proc/%s/stat" % pid) as stat_file:
                stat_contents = stat_file.read()
            timestamp = get_starttime(stat_contents)

    if exe is None:
        exe = get_process_path(proc_pid_fd)
    exe = exe.replace('/', '_').replace('.', '_')

    if uid is None:
        uid = os.getuid()

    # This is similar to systemd-coredump, but with the exe name instead
    # of the command name
    core_name = ('core.%s.%s.%s.%s.%s' % (exe, uid, get_boot_id(),
                                          str(pid), str(timestamp)))

    core_path = os.path.join(core_dir, core_name)

    return (core_name, core_path)


def find_core_files_by_uid(uid):
    '''Searches the core file directory for files that belong to a
       specified uid. Returns a list of lists containing the filename and
       the file modification time.'''
    uid = str(uid)
    core_files = []
    uid_files = []

    if os.path.exists(core_dir):
        core_files = os.listdir(path=core_dir)

    for f in core_files:
        try:
            if f.split('.')[2] == uid:
                time = os.path.getmtime(os.path.join(core_dir, f))
                uid_files.append([f, time])
        except (IndexError, FileNotFoundError):
            continue
    return uid_files


def clean_core_directory(uid):
    '''Removes old files from the core directory if there are more than
       the maximum allowed per uid'''

    uid_files = find_core_files_by_uid(uid)
    sorted_files = sorted(uid_files, key=itemgetter(1))

    # Subtract a extra one to make room for the new core file
    if len(uid_files) > max_corefiles_per_uid - 1:
        for x in range(len(uid_files) - max_corefiles_per_uid + 1):
            os.remove(os.path.join(core_dir, sorted_files[0][0]))
            sorted_files.remove(sorted_files[0])


def shared_libraries(path):
    '''Get libraries with which the specified binary is linked.

    Return a library name -> path mapping, for example 'libc.so.6' ->
    '/lib/x86_64-linux-gnu/libc.so.6'.
    '''
    libs = {}

    ldd = subprocess.Popen(['ldd', path], stdout=subprocess.PIPE,
                           stderr=subprocess.STDOUT,
                           universal_newlines=True)
    for line in ldd.stdout:
        try:
            name, rest = line.split('=>', 1)
        except ValueError:
            continue

        name = name.strip()
        # exclude linux-vdso since that is a virtual so
        if 'linux-vdso' in name:
            continue
        # this is usually "path (address)"
        rest = rest.split()[0].strip()
        if rest.startswith('('):
            continue
        libs[name] = rest
    ldd.stdout.close()
    ldd.wait()

    if ldd.returncode != 0:
        return {}
    return libs


def links_with_shared_library(path, lib):
    '''Check if the binary at path links with the library named lib.

    path should be a fully qualified path (e.g. report['ExecutablePath']),
    lib may be of the form 'lib<name>' or 'lib<name>.so.<version>'
    '''
    libs = shared_libraries(path)

    if lib in libs:
        return True

    for linked_lib in libs:
        if linked_lib.startswith(lib + '.so.'):
            return True

    return False