__init__.py 56.3 KB
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#!/usr/bin/env python
#
# Copyright 2017-2018 Amazon.com, Inc. and its affiliates. All Rights Reserved.
#
# Licensed under the MIT License. See the LICENSE accompanying this file
# for the specific language governing permissions and limitations under
# the License.
#
#
# Copy this script to /sbin/mount.efs and make sure it is executable.
#
# You will be able to mount an EFS file system by its short name, by adding it
# to /etc/fstab. The syntax of an fstab entry is:
#
# [Device] [Mount Point] [File System Type] [Options] [Dump] [Pass]
#
# Add an entry like this:
#
#   fs-deadbeef     /mount_point    efs     _netdev         0   0
#
# Using the 'efs' type will cause '/sbin/mount.efs' to be called by 'mount -a'
# for this file system. The '_netdev' option tells the init system that the
# 'efs' type is a networked file system type. This has been tested with systemd
# (Amazon Linux 2, CentOS 7, RHEL 7, Debian 9, and Ubuntu 16.04), and upstart
# (Amazon Linux 2017.09).
#
# Once there is an entry in fstab, the file system can be mounted with:
#
#   sudo mount /mount_point
#
# The script will add recommended mount options, if not provided in fstab.

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import base64
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import errno
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import hashlib
import hmac
import itertools
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import json
import logging
import os
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import pwd
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import random
import re
import socket
import subprocess
import sys
import threading
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import time
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from contextlib import contextmanager
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from datetime import datetime, timedelta
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from logging.handlers import RotatingFileHandler

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try:
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    import ConfigParser
    from ConfigParser import NoOptionError, NoSectionError
except ImportError:
    from configparser import ConfigParser, NoOptionError, NoSectionError
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try:
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    from urllib.parse import quote_plus
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except ImportError:
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    from urllib import quote_plus
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try:
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    from urllib2 import URLError, HTTPError, build_opener, urlopen, Request, HTTPHandler
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except ImportError:
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    from urllib.request import urlopen, Request
    from urllib.error import URLError, HTTPError
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VERSION = '1.24'
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SERVICE = 'elasticfilesystem'
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CONFIG_FILE = '/etc/amazon/efs/efs-utils.conf'
CONFIG_SECTION = 'mount'
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CLIENT_INFO_SECTION = 'client-info'
CLIENT_SOURCE_STR_LEN_LIMIT = 100
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LOG_DIR = '/var/log/amazon/efs'
LOG_FILE = 'mount.log'

STATE_FILE_DIR = '/var/run/efs'

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PRIVATE_KEY_FILE = '/etc/amazon/efs/privateKey.pem'
DATE_ONLY_FORMAT = '%Y%m%d'
SIGV4_DATETIME_FORMAT = '%Y%m%dT%H%M%SZ'
CERT_DATETIME_FORMAT = '%y%m%d%H%M%SZ'

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AWS_CREDENTIALS_FILE = os.path.expanduser(os.path.join('~' + pwd.getpwuid(os.getuid()).pw_name, '.aws', 'credentials'))
AWS_CONFIG_FILE = os.path.expanduser(os.path.join('~' + pwd.getpwuid(os.getuid()).pw_name, '.aws', 'config'))

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CA_CONFIG_BODY = """dir = %s
RANDFILE = $dir/database/.rand

[ ca ]
default_ca = local_ca

[ local_ca ]
database = $dir/database/index.txt
serial = $dir/database/serial
private_key = %s
cert = $dir/certificate.pem
new_certs_dir = $dir/certs
default_md = sha256
preserve = no
policy = efsPolicy
x509_extensions = v3_ca

[ efsPolicy ]
CN = supplied

[ req ]
prompt = no
distinguished_name = req_distinguished_name

[ req_distinguished_name ]
CN = %s

%s

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%s

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%s
"""

# SigV4 Auth
ALGORITHM = 'AWS4-HMAC-SHA256'
AWS4_REQUEST = 'aws4_request'

HTTP_REQUEST_METHOD = 'GET'
CANONICAL_URI = '/'
CANONICAL_HEADERS_DICT = {
    'host': '%s'
}
CANONICAL_HEADERS = '\n'.join(['%s:%s' % (k, v) for k, v in sorted(CANONICAL_HEADERS_DICT.items())])
SIGNED_HEADERS = ';'.join(CANONICAL_HEADERS_DICT.keys())
REQUEST_PAYLOAD = ''

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FS_ID_RE = re.compile('^(?P<fs_id>fs-[0-9a-f]+)$')
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EFS_FQDN_RE = re.compile(r'^(?P<fs_id>fs-[0-9a-f]+)\.efs\.(?P<region>[a-z0-9-]+)\.(?P<dns_name_suffix>[a-z0-9.]+)$')
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AP_ID_RE = re.compile('^fsap-[0-9a-f]{17}$')
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CREDENTIALS_KEYS = ['AccessKeyId', 'SecretAccessKey', 'Token']
ECS_URI_ENV = 'AWS_CONTAINER_CREDENTIALS_RELATIVE_URI'
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ECS_TASK_METADATA_API = 'http://169.254.170.2'
INSTANCE_METADATA_TOKEN_URL = 'http://169.254.169.254/latest/api/token'
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INSTANCE_METADATA_SERVICE_URL = 'http://169.254.169.254/latest/dynamic/instance-identity/document/'
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INSTANCE_IAM_URL = 'http://169.254.169.254/latest/meta-data/iam/security-credentials/'
SECURITY_CREDS_ECS_URI_HELP_URL = 'https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task-iam-roles.html'
SECURITY_CREDS_IAM_ROLE_HELP_URL = 'https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html'
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DEFAULT_STUNNEL_VERIFY_LEVEL = 2
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DEFAULT_STUNNEL_CAFILE = '/etc/amazon/efs/efs-utils.crt'
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NOT_BEFORE_MINS = 15
NOT_AFTER_HOURS = 3

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EFS_ONLY_OPTIONS = [
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    'accesspoint',
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    'awscredsuri',
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    'awsprofile',
    'cafile',
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    'iam',
    'netns',
    'noocsp',
    'ocsp',
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    'tls',
    'tlsport',
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    'verify'
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]

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UNSUPPORTED_OPTIONS = [
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    'capath'
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]

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STUNNEL_GLOBAL_CONFIG = {
    'fips': 'no',
    'foreground': 'yes',
    'socket': [
        'l:SO_REUSEADDR=yes',
        'a:SO_BINDTODEVICE=lo',
    ],
}

STUNNEL_EFS_CONFIG = {
    'client': 'yes',
    'accept': '127.0.0.1:%s',
    'connect': '%s:2049',
    'sslVersion': 'TLSv1.2',
    'renegotiation': 'no',
    'TIMEOUTbusy': '20',
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    'TIMEOUTclose': '0',
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    'TIMEOUTidle': '70',
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    'delay': 'yes',
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}

WATCHDOG_SERVICE = 'amazon-efs-mount-watchdog'
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SYSTEM_RELEASE_PATH = '/etc/system-release'
RHEL8_RELEASE_NAME = 'Red Hat Enterprise Linux release 8'
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def fatal_error(user_message, log_message=None, exit_code=1):
    if log_message is None:
        log_message = user_message

    sys.stderr.write('%s\n' % user_message)
    logging.error(log_message)
    sys.exit(exit_code)


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def get_target_region(config):
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    def _fatal_error(message):
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        fatal_error('Error retrieving region. Please set the "region" parameter in the efs-utils configuration file.', message)

    metadata_exception = 'Unknown error'
    try:
        return config.get(CONFIG_SECTION, 'region')
    except NoOptionError:
        pass

    try:
        return get_region_from_instance_metadata()
    except Exception as e:
        metadata_exception = e
        logging.warn('Region not found in config file and metadata service call failed, falling back '
                     'to legacy "dns_name_format" check')
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    try:
        region = get_region_from_legacy_dns_format(config)
        sys.stdout.write('Warning: region obtained from "dns_name_format" field. Please set the "region" '
                         'parameter in the efs-utils configuration file.')
        return region
    except Exception:
        logging.warn('Legacy check for region in "dns_name_format" failed')

    _fatal_error(metadata_exception)


def get_region_from_instance_metadata():
    err_msg = None
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    try:
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        headers = {}
        instance_identity = get_aws_ec2_metadata(headers)
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        return instance_identity['region']
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    except HTTPError as e:
        # 401:Unauthorized, the GET request uses an invalid token, so generate a new one
        if e.code == 401:
            token = get_aws_ec2_metadata_token()
            headers = {'X-aws-ec2-metadata-token': token}
            instance_identity = get_aws_ec2_metadata(headers)
            return instance_identity['region']
        err_msg = 'Unable to reach instance metadata service at %s: status=%d, reason is %s' \
                  % (INSTANCE_METADATA_SERVICE_URL, e.code, e.reason)
    except URLError as e:
        err_msg = 'Unable to reach instance metadata service at %s, reason is %s' % (INSTANCE_METADATA_SERVICE_URL, e.reason)
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    except ValueError as e:
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        err_msg = 'Error parsing json: %s' % (e,)
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    except KeyError as e:
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        err_msg = 'Region not present in %s: %s' % (instance_identity, e)

    if err_msg:
        raise Exception(err_msg)


def get_region_from_legacy_dns_format(config):
    """
    For backwards compatibility check dns_name_format to obtain the target region. This functionality
    should only be used if region is not present in the config file and metadata calls fail.
    """
    dns_name_format = config.get(CONFIG_SECTION, 'dns_name_format')
    if '{region}' not in dns_name_format:
        split_dns_name_format = dns_name_format.split('.')
        if '{dns_name_suffix}' in dns_name_format:
            return split_dns_name_format[-2]
        elif 'amazonaws.com' in dns_name_format:
            return split_dns_name_format[-3]
    raise Exception('Region not found in dns_name_format')
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def get_aws_ec2_metadata_token():
    try:
        opener = build_opener(HTTPHandler)
        request = Request(INSTANCE_METADATA_TOKEN_URL)
        request.add_header('X-aws-ec2-metadata-token-ttl-seconds', 21600)
        request.get_method = lambda: 'PUT'
        res = opener.open(request)
        return res.read()
    except NameError:
        headers = {'X-aws-ec2-metadata-token-ttl-seconds': 21600}
        req = Request(INSTANCE_METADATA_TOKEN_URL, headers=headers, method='PUT')
        res = urlopen(req)
        return res.read()


def get_aws_ec2_metadata(headers):
    request = Request(INSTANCE_METADATA_SERVICE_URL, headers=headers)
    response = urlopen(request, timeout=1)
    data = response.read()
    if type(data) is str:
        instance_identity = json.loads(data)
    else:
        instance_identity = json.loads(data.decode(response.headers.get_content_charset() or 'us-ascii'))
    return instance_identity


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def get_aws_security_credentials(use_iam, awsprofile=None, aws_creds_uri=None):
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    """
    Lookup AWS security credentials (access key ID and secret access key). Adapted credentials provider chain from:
    https://boto3.amazonaws.com/v1/documentation/api/latest/guide/configuration.html and
    https://docs.aws.amazon.com/sdk-for-java/v1/developer-guide/credentials.html
    """
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    if not use_iam:
        return None, None

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    # attempt to lookup AWS security credentials through the credentials URI the ECS agent generated
    if aws_creds_uri:
        return get_aws_security_credentials_from_ecs(aws_creds_uri, True)

    # attempt to lookup AWS security credentials in AWS credentials file (~/.aws/credentials)
    # and configs file (~/.aws/config) with given awsprofile
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    if awsprofile:
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        return get_aws_security_credentials_from_awsprofile(awsprofile, True)

    # attempt to lookup AWS security credentials through AWS_CONTAINER_CREDENTIALS_RELATIVE_URI environment variable
    if ECS_URI_ENV in os.environ:
        credentials, credentials_source = get_aws_security_credentials_from_ecs(os.environ[ECS_URI_ENV], False)
        if credentials and credentials_source:
            return credentials, credentials_source

    # attempt to lookup AWS security credentials with IAM role name attached to instance
    # through IAM role name security credentials lookup uri
    iam_role_name = get_iam_role_name()
    if iam_role_name:
        credentials, credentials_source = get_aws_security_credentials_from_instance_metadata(iam_role_name)
        if credentials and credentials_source:
            return credentials, credentials_source
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    error_msg = 'AWS Access Key ID and Secret Access Key are not found in AWS credentials file (%s), config file (%s), ' \
                'from ECS credentials relative uri, or from the instance security credentials service' % \
                (AWS_CREDENTIALS_FILE, AWS_CONFIG_FILE)
    fatal_error(error_msg, error_msg)


def get_aws_security_credentials_from_awsprofile(awsprofile, is_fatal=False):
    for file_path in [AWS_CREDENTIALS_FILE, AWS_CONFIG_FILE]:
        if os.path.exists(file_path):
            credentials = credentials_file_helper(file_path, awsprofile)
            if credentials['AccessKeyId']:
                return credentials, os.path.basename(file_path) + ':' + awsprofile

    # Fail if credentials cannot be fetched from the given awsprofile
    if is_fatal:
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        log_message = 'AWS security credentials not found in %s or %s under named profile [%s]' % \
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                    (AWS_CREDENTIALS_FILE, AWS_CONFIG_FILE, awsprofile)
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        fatal_error(log_message)
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    else:
        return None, None
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def get_aws_security_credentials_from_ecs(aws_creds_uri, is_fatal=False):
    ecs_uri = ECS_TASK_METADATA_API + aws_creds_uri
    ecs_unsuccessful_resp = 'Unsuccessful retrieval of AWS security credentials at %s.' % ecs_uri
    ecs_url_error_msg = 'Unable to reach %s to retrieve AWS security credentials. See %s for more info.' \
                        % (ecs_uri, SECURITY_CREDS_ECS_URI_HELP_URL)
    ecs_security_dict = url_request_helper(ecs_uri, ecs_unsuccessful_resp, ecs_url_error_msg)
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    if ecs_security_dict and all(k in ecs_security_dict for k in CREDENTIALS_KEYS):
        return ecs_security_dict, 'ecs:' + aws_creds_uri
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    # Fail if credentials cannot be fetched from the given aws_creds_uri
    if is_fatal:
        fatal_error(ecs_unsuccessful_resp, ecs_unsuccessful_resp)
    else:
        return None, None


def get_aws_security_credentials_from_instance_metadata(iam_role_name):
    security_creds_lookup_url = INSTANCE_IAM_URL + str(iam_role_name)
    unsuccessful_resp = 'Unsuccessful retrieval of AWS security credentials at %s.' % security_creds_lookup_url
    url_error_msg = 'Unable to reach %s to retrieve AWS security credentials. See %s for more info.',\
                    security_creds_lookup_url, SECURITY_CREDS_IAM_ROLE_HELP_URL
    iam_security_dict = url_request_helper(security_creds_lookup_url, unsuccessful_resp, url_error_msg)

    if iam_security_dict and all(k in iam_security_dict for k in CREDENTIALS_KEYS):
        return iam_security_dict, 'metadata:'
    else:
        return None, None


def get_iam_role_name():
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    iam_role_unsuccessful_resp = 'Unsuccessful retrieval of IAM role name at %s.' % INSTANCE_IAM_URL
    iam_role_url_error_msg = 'Unable to reach %s to retrieve IAM role name. See %s for more info.', INSTANCE_IAM_URL, \
                             SECURITY_CREDS_IAM_ROLE_HELP_URL
    iam_role_name = url_request_helper(INSTANCE_IAM_URL, iam_role_unsuccessful_resp, iam_role_url_error_msg)
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    return iam_role_name
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def credentials_file_helper(file_path, awsprofile):
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    aws_credentials_configs = read_config(file_path)
    credentials = {'AccessKeyId': None, 'SecretAccessKey': None, 'Token': None}

    try:
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        access_key = aws_credentials_configs.get(awsprofile, 'aws_access_key_id')
        secret_key = aws_credentials_configs.get(awsprofile, 'aws_secret_access_key')
        session_token = aws_credentials_configs.get(awsprofile, 'aws_session_token')
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        credentials['AccessKeyId'] = access_key
        credentials['SecretAccessKey'] = secret_key
        credentials['Token'] = session_token
    except NoOptionError as e:
        if 'aws_access_key_id' in str(e) or 'aws_secret_access_key' in str(e):
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            logging.debug('aws_access_key_id or aws_secret_access_key not found in %s under named profile [%s]', file_path,
                          awsprofile)
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        if 'aws_session_token' in str(e):
            logging.debug('aws_session_token not found in %s', file_path)
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            credentials['AccessKeyId'] = aws_credentials_configs.get(awsprofile, 'aws_access_key_id')
            credentials['SecretAccessKey'] = aws_credentials_configs.get(awsprofile, 'aws_secret_access_key')
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    except NoSectionError:
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        logging.debug('No [%s] section found in config file %s', awsprofile, file_path)
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    return credentials


def get_correct_default_case_combination(aws_credentials_configs):
    default_str = 'default'
    for perm in map(''.join, itertools.product(*zip(default_str.upper(), default_str.lower()))):
        try:
            access_key = aws_credentials_configs.get(perm, 'aws_access_key_id')
            if access_key is not None:
                return perm
        except (NoSectionError, NoOptionError):
            continue

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    return None


def get_aws_profile(options, use_iam):
    awsprofile = options.get('awsprofile')
    if not awsprofile and use_iam:
        for file_path in [AWS_CREDENTIALS_FILE, AWS_CONFIG_FILE]:
            aws_credentials_configs = read_config(file_path)
            awsprofile = get_correct_default_case_combination(aws_credentials_configs)
            if awsprofile:
                break

    return awsprofile
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def url_request_helper(url, unsuccessful_resp, url_error_msg):
    try:
        request_resp = urlopen(url, timeout=1)

        if request_resp.getcode() != 200:
            logging.debug(unsuccessful_resp + ' %s: ResponseCode=%d', url, request_resp.getcode())
            return None

        resp_body = request_resp.read()
        try:
            if type(resp_body) is str:
                resp_dict = json.loads(resp_body)
            else:
                resp_dict = json.loads(resp_body.decode(request_resp.headers.get_content_charset() or 'us-ascii'))

            return resp_dict
        except ValueError as e:
            logging.debug('Error parsing json: %s, returning raw response body: %s' % (e, str(resp_body)))
            return resp_body
    except URLError as e:
        logging.debug('%s %s', url_error_msg, e)
        return None


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def parse_options(options):
    opts = {}
    for o in options.split(','):
        if '=' in o:
            k, v = o.split('=')
            opts[k] = v
        else:
            opts[o] = None
    return opts


def get_tls_port_range(config):
    lower_bound = config.getint(CONFIG_SECTION, 'port_range_lower_bound')
    upper_bound = config.getint(CONFIG_SECTION, 'port_range_upper_bound')

    if lower_bound >= upper_bound:
        fatal_error('Configuration option "port_range_upper_bound" defined as %d '
                    'must be strictly greater than "port_range_lower_bound" defined as %d.'
                    % (upper_bound, lower_bound))

    return lower_bound, upper_bound


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def choose_tls_port(config, options):
    if 'tlsport' in options:
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        ports_to_try = [int(options['tlsport'])]
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    else:
        lower_bound, upper_bound = get_tls_port_range(config)
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        tls_ports = list(range(lower_bound, upper_bound))
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        # Choose a random midpoint, and then try ports in-order from there
        mid = random.randrange(len(tls_ports))
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        ports_to_try = tls_ports[mid:] + tls_ports[:mid]
        assert len(tls_ports) == len(ports_to_try)
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    sock = socket.socket()
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    for tls_port in ports_to_try:
        try:
            sock.bind(('localhost', tls_port))
            sock.close()
            return tls_port
        except socket.error:
            continue

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    sock.close()

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    if 'tlsport' in options:
        fatal_error('Specified port [%s] is unavailable. Try selecting a different port.' % options['tlsport'])
    else:
        fatal_error('Failed to locate an available port in the range [%d, %d], try specifying a different port range in %s'
                    % (lower_bound, upper_bound, CONFIG_FILE))


def is_ocsp_enabled(config, options):
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    if 'ocsp' in options:
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        return True
    elif 'noocsp' in options:
        return False
    else:
        return config.getboolean(CONFIG_SECTION, 'stunnel_check_cert_validity')
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def get_mount_specific_filename(fs_id, mountpoint, tls_port):
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    return '%s.%s.%d' % (fs_id, os.path.abspath(mountpoint).replace(os.sep, '.').lstrip('.'), tls_port)
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def serialize_stunnel_config(config, header=None):
    lines = []

    if header:
        lines.append('[%s]' % header)

    for k, v in config.items():
        if type(v) is list:
            for item in v:
                lines.append('%s = %s' % (k, item))
        else:
            lines.append('%s = %s' % (k, v))

    return lines


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def add_stunnel_ca_options(efs_config, config, options):
    if 'cafile' in options:
        stunnel_cafile = options['cafile']
    else:
        try:
            stunnel_cafile = config.get(CONFIG_SECTION, 'stunnel_cafile')
        except NoOptionError:
            logging.debug('No CA file configured, using default CA file %s', DEFAULT_STUNNEL_CAFILE)
            stunnel_cafile = DEFAULT_STUNNEL_CAFILE

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    if not os.path.exists(stunnel_cafile):
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        fatal_error('Failed to find certificate authority file for verification',
                    'Failed to find CAfile "%s"' % stunnel_cafile)

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    efs_config['CAfile'] = stunnel_cafile


def is_stunnel_option_supported(stunnel_output, stunnel_option_name):
    supported = False
    for line in stunnel_output:
        if line.startswith(stunnel_option_name):
            supported = True
            break

    if not supported:
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        logging.warning('stunnel does not support "%s"', stunnel_option_name)
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    return supported


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def get_version_specific_stunnel_options():
    stunnel_command = [_stunnel_bin(), '-help']
    proc = subprocess.Popen(stunnel_command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, close_fds=True)
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    proc.wait()
    _, err = proc.communicate()
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    stunnel_output = err.splitlines()
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    check_host_supported = is_stunnel_option_supported(stunnel_output, b'checkHost')
    ocsp_aia_supported = is_stunnel_option_supported(stunnel_output, b'OCSPaia')
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    return check_host_supported, ocsp_aia_supported
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def _stunnel_bin():
    return find_command_path('stunnel',
                             'Please install it following the instructions at '
                             'https://docs.aws.amazon.com/efs/latest/ug/using-amazon-efs-utils.html#upgrading-stunnel')


def find_command_path(command, install_method):
    try:
        env_path = '/sbin:/usr/sbin:/usr/local/sbin:/root/bin:/usr/local/bin:/usr/bin:/bin'
        os.putenv('PATH', env_path)
        path = subprocess.check_output(['which', command])
    except subprocess.CalledProcessError as e:
        fatal_error('Failed to locate %s in %s - %s' % (command, env_path, install_method), e)
    return path.strip().decode()


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def get_system_release_version():
    system_release_version = 'unknown'
    try:
        with open(SYSTEM_RELEASE_PATH) as f:
            system_release_version = f.read().strip()
    except IOError:
        logging.debug('Unable to read %s', SYSTEM_RELEASE_PATH)

    return system_release_version


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def write_stunnel_config_file(config, state_file_dir, fs_id, mountpoint, tls_port, dns_name, verify_level, ocsp_enabled,
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                              options, log_dir=LOG_DIR, cert_details=None):
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    """
    Serializes stunnel configuration to a file. Unfortunately this does not conform to Python's config file format, so we have to
    hand-serialize it.
    """

    mount_filename = get_mount_specific_filename(fs_id, mountpoint, tls_port)

    global_config = dict(STUNNEL_GLOBAL_CONFIG)
    if config.getboolean(CONFIG_SECTION, 'stunnel_debug_enabled'):
        global_config['debug'] = 'debug'
        global_config['output'] = os.path.join(log_dir, '%s.stunnel.log' % mount_filename)

    efs_config = dict(STUNNEL_EFS_CONFIG)
    efs_config['accept'] = efs_config['accept'] % tls_port
    efs_config['connect'] = efs_config['connect'] % dns_name
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    efs_config['verify'] = verify_level
    if verify_level > 0:
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        add_stunnel_ca_options(efs_config, config, options)

    if cert_details:
        efs_config['cert'] = cert_details['certificate']
        efs_config['key'] = cert_details['privateKey']
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    check_host_supported, ocsp_aia_supported = get_version_specific_stunnel_options()
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    tls_controls_message = 'WARNING: Your client lacks sufficient controls to properly enforce TLS. Please upgrade stunnel, ' \
        'or disable "%%s" in %s.\nSee %s for more detail.' % (CONFIG_FILE,
                                                              'https://docs.aws.amazon.com/console/efs/troubleshooting-tls')
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    if config.getboolean(CONFIG_SECTION, 'stunnel_check_cert_hostname'):
        if check_host_supported:
            efs_config['checkHost'] = dns_name
        else:
            fatal_error(tls_controls_message % 'stunnel_check_cert_hostname')
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    # Only use the config setting if the override is not set
    if ocsp_enabled:
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        if ocsp_aia_supported:
            efs_config['OCSPaia'] = 'yes'
        else:
            fatal_error(tls_controls_message % 'stunnel_check_cert_validity')
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    if RHEL8_RELEASE_NAME not in get_system_release_version():
        efs_config['libwrap'] = 'no'

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    stunnel_config = '\n'.join(serialize_stunnel_config(global_config) + serialize_stunnel_config(efs_config, 'efs'))
    logging.debug('Writing stunnel configuration:\n%s', stunnel_config)

    stunnel_config_file = os.path.join(state_file_dir, 'stunnel-config.%s' % mount_filename)

    with open(stunnel_config_file, 'w') as f:
        f.write(stunnel_config)

    return stunnel_config_file


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def write_tls_tunnel_state_file(fs_id, mountpoint, tls_port, tunnel_pid, command, files, state_file_dir, cert_details=None):
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    """
    Return the name of the temporary file containing TLS tunnel state, prefixed with a '~'. This file needs to be renamed to a
    non-temporary version following a successful mount.
    """
    state_file = '~' + get_mount_specific_filename(fs_id, mountpoint, tls_port)

    state = {
        'pid': tunnel_pid,
        'cmd': command,
        'files': files,
    }

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    if cert_details:
        state.update(cert_details)

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    with open(os.path.join(state_file_dir, state_file), 'w') as f:
        json.dump(state, f)

    return state_file


def test_tunnel_process(tunnel_proc, fs_id):
    tunnel_proc.poll()
    if tunnel_proc.returncode is not None:
        out, err = tunnel_proc.communicate()
        fatal_error('Failed to initialize TLS tunnel for %s' % fs_id,
                    'Failed to start TLS tunnel (errno=%d). stdout="%s" stderr="%s"'
                    % (tunnel_proc.returncode, out.strip(), err.strip()))


def poll_tunnel_process(tunnel_proc, fs_id, mount_completed):
    """
    poll the tunnel process health every .5s during the mount attempt to fail fast if the tunnel dies - since this is not called
    from the main thread, if the tunnel fails, exit uncleanly with os._exit
    """
    while not mount_completed.is_set():
        try:
            test_tunnel_process(tunnel_proc, fs_id)
        except SystemExit as e:
            os._exit(e.code)
        mount_completed.wait(.5)


def get_init_system(comm_file='/proc/1/comm'):
    init_system = 'unknown'
    try:
        with open(comm_file) as f:
            init_system = f.read().strip()
    except IOError:
        logging.warning('Unable to read %s', comm_file)

    logging.debug('Identified init system: %s', init_system)
    return init_system


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def check_network_target(fs_id):
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    with open(os.devnull, 'w') as devnull:
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        rc = subprocess.call(['systemctl', 'status', 'network.target'], stdout=devnull, stderr=devnull, close_fds=True)
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    if rc != 0:
        fatal_error('Failed to mount %s because the network was not yet available, add "_netdev" to your mount options' % fs_id,
                    exit_code=0)


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def check_network_status(fs_id, init_system):
    if init_system != 'systemd':
        logging.debug('Not testing network on non-systemd init systems')
        return

    check_network_target(fs_id)


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def start_watchdog(init_system):
    if init_system == 'init':
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        proc = subprocess.Popen(
                ['/sbin/status', WATCHDOG_SERVICE], stdout=subprocess.PIPE, stderr=subprocess.PIPE, close_fds=True)
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        status, _ = proc.communicate()
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        if 'stop' in status:
            with open(os.devnull, 'w') as devnull:
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                subprocess.Popen(['/sbin/start', WATCHDOG_SERVICE], stdout=devnull, stderr=devnull, close_fds=True)
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        elif 'start' in status:
            logging.debug('%s is already running', WATCHDOG_SERVICE)

    elif init_system == 'systemd':
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        rc = subprocess.call(['systemctl', 'is-active', '--quiet', WATCHDOG_SERVICE], close_fds=True)
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        if rc != 0:
            with open(os.devnull, 'w') as devnull:
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                subprocess.Popen(['systemctl', 'start', WATCHDOG_SERVICE], stdout=devnull, stderr=devnull, close_fds=True)
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        else:
            logging.debug('%s is already running', WATCHDOG_SERVICE)

    else:
        error_message = 'Could not start %s, unrecognized init system "%s"' % (WATCHDOG_SERVICE, init_system)
        sys.stderr.write('%s\n' % error_message)
        logging.warning(error_message)


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def create_required_directory(config, directory):
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    mode = 0o750
    try:
        mode_str = config.get(CONFIG_SECTION, 'state_file_dir_mode')
        try:
            mode = int(mode_str, 8)
        except ValueError:
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            logging.warning('Bad state_file_dir_mode "%s" in config file "%s"', mode_str, CONFIG_FILE)
    except NoOptionError:
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        pass

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    try:
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        os.makedirs(directory, mode)
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    except OSError as e:
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        if errno.EEXIST != e.errno or not os.path.isdir(directory):
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            raise
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@contextmanager
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def bootstrap_tls(config, init_system, dns_name, fs_id, mountpoint, options, state_file_dir=STATE_FILE_DIR):
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    tls_port = choose_tls_port(config, options)
    # override the tlsport option so that we can later override the port the NFS client uses to connect to stunnel.
    # if the user has specified tlsport=X at the command line this will just re-set tlsport to X.
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    options['tlsport'] = tls_port
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    use_iam = 'iam' in options
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    ap_id = options.get('accesspoint')
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    cert_details = {}

    if use_iam or ap_id:
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        aws_creds_uri = options.get('awscredsuri')
        if aws_creds_uri:
            kwargs = {'aws_creds_uri': aws_creds_uri}
        else:
            kwargs = {'awsprofile': get_aws_profile(options, use_iam)}

        security_credentials, credentials_source = get_aws_security_credentials(use_iam, **kwargs)
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        # additional symbol appended to avoid naming collisions
        cert_details['mountStateDir'] = get_mount_specific_filename(fs_id, mountpoint, tls_port) + '+'
        # common name for certificate signing request is max 64 characters
        cert_details['commonName'] = socket.gethostname()[0:64]
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        cert_details['region'] = get_target_region(config)
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        cert_details['certificateCreationTime'] = create_certificate(config, cert_details['mountStateDir'],
                                                                     cert_details['commonName'], cert_details['region'], fs_id,
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                                                                     security_credentials, ap_id=ap_id, base_path=state_file_dir)
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        cert_details['certificate'] = os.path.join(state_file_dir, cert_details['mountStateDir'], 'certificate.pem')
        cert_details['privateKey'] = get_private_key_path()
        cert_details['fsId'] = fs_id

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        if credentials_source:
            cert_details['awsCredentialsMethod'] = credentials_source
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        if ap_id:
            cert_details['accessPoint'] = ap_id
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    start_watchdog(init_system)

    if not os.path.exists(state_file_dir):
        create_required_directory(config, state_file_dir)

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    verify_level = int(options.get('verify', DEFAULT_STUNNEL_VERIFY_LEVEL))
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    ocsp_enabled = is_ocsp_enabled(config, options)
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    stunnel_config_file = write_stunnel_config_file(config, state_file_dir, fs_id, mountpoint, tls_port, dns_name, verify_level,
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                                                    ocsp_enabled, options, cert_details=cert_details)
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    tunnel_args = [_stunnel_bin(), stunnel_config_file]
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    if 'netns' in options:
        tunnel_args = ['nsenter', '--net=' + options['netns']] + tunnel_args
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    # launch the tunnel in a process group so if it has any child processes, they can be killed easily by the mount watchdog
    logging.info('Starting TLS tunnel: "%s"', ' '.join(tunnel_args))
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    tunnel_proc = subprocess.Popen(
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        tunnel_args, stdout=subprocess.PIPE, stderr=subprocess.PIPE, preexec_fn=os.setsid, close_fds=True)
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    logging.info('Started TLS tunnel, pid: %d', tunnel_proc.pid)

    temp_tls_state_file = write_tls_tunnel_state_file(fs_id, mountpoint, tls_port, tunnel_proc.pid, tunnel_args,
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                                                      [stunnel_config_file], state_file_dir, cert_details=cert_details)
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    try:
        yield tunnel_proc
    finally:
        os.rename(os.path.join(state_file_dir, temp_tls_state_file), os.path.join(state_file_dir, temp_tls_state_file[1:]))


def get_nfs_mount_options(options):
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    # If you change these options, update the man page as well at man/mount.efs.8
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    if 'nfsvers' not in options and 'vers' not in options:
        options['nfsvers'] = '4.1'
    if 'rsize' not in options:
        options['rsize'] = '1048576'
    if 'wsize' not in options:
        options['wsize'] = '1048576'
    if 'soft' not in options and 'hard' not in options:
        options['hard'] = None
    if 'timeo' not in options:
        options['timeo'] = '600'
    if 'retrans' not in options:
        options['retrans'] = '2'
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    if 'noresvport' not in options:
        options['noresvport'] = None
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    if 'tls' in options:
        options['port'] = options['tlsport']

    def to_nfs_option(k, v):
        if v is None:
            return k
        return '%s=%s' % (str(k), str(v))

    nfs_options = [to_nfs_option(k, v) for k, v in options.items() if k not in EFS_ONLY_OPTIONS]

    return ','.join(nfs_options)


def mount_nfs(dns_name, path, mountpoint, options):
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    if 'tls' in options:
        mount_path = '127.0.0.1:%s' % path
    else:
        mount_path = '%s:%s' % (dns_name, path)

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    command = ['/sbin/mount.nfs4', mount_path, mountpoint, '-o', get_nfs_mount_options(options)]
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    if 'netns' in options:
        command = ['nsenter', '--net=' + options['netns']] + command

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    logging.info('Executing: "%s"', ' '.join(command))

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    proc = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, close_fds=True)
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    out, err = proc.communicate()
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    if proc.returncode == 0:
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        logging.info('Successfully mounted %s at %s', dns_name, mountpoint)
    else:
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        message = 'Failed to mount %s at %s: returncode=%d, stderr="%s"' % (dns_name, mountpoint, proc.returncode, err.strip())
        fatal_error(err.strip(), message, proc.returncode)
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def usage(out, exit_code=1):
    out.write('Usage: mount.efs [--version] [-h|--help] <fsname> <mountpoint> [-o <options>]\n')
    sys.exit(exit_code)


def parse_arguments_early_exit(args=None):
    """Parse arguments, checking for early exit conditions only"""
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    if args is None:
        args = sys.argv

    if '-h' in args[1:] or '--help' in args[1:]:
        usage(out=sys.stdout, exit_code=0)

    if '--version' in args[1:]:
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        sys.stdout.write('%s Version: %s\n' % (args[0], VERSION))
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        sys.exit(0)

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def parse_arguments(config, args=None):
    """Parse arguments, return (fsid, path, mountpoint, options)"""
    if args is None:
        args = sys.argv

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    fsname = None
    mountpoint = None
    options = {}

    if len(args) > 1:
        fsname = args[1]
    if len(args) > 2:
        mountpoint = args[2]
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    if len(args) > 4 and '-o' in args[:-1]:
        options_index = args.index('-o') + 1
        options = parse_options(args[options_index])
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    if not fsname or not mountpoint:
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        usage(out=sys.stderr)
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    fs_id, path = match_device(config, fsname)
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    return fs_id, path, mountpoint, options


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def get_client_info(config):
    client_info = {}

    # source key/value pair in config file
    if config.has_option(CLIENT_INFO_SECTION, 'source'):
        client_source = config.get(CLIENT_INFO_SECTION, 'source')
        if 0 < len(client_source) <= CLIENT_SOURCE_STR_LEN_LIMIT:
            client_info['source'] = client_source

    return client_info


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def create_certificate(config, mount_name, common_name, region, fs_id, security_credentials, ap_id, base_path=STATE_FILE_DIR):
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    current_time = get_utc_now()
    tls_paths = tls_paths_dictionary(mount_name, base_path)

    certificate_config = os.path.join(tls_paths['mount_dir'], 'config.conf')
    certificate_signing_request = os.path.join(tls_paths['mount_dir'], 'request.csr')
    certificate = os.path.join(tls_paths['mount_dir'], 'certificate.pem')

    ca_dirs_check(config, tls_paths['database_dir'], tls_paths['certs_dir'])
    ca_supporting_files_check(tls_paths['index'], tls_paths['index_attr'], tls_paths['serial'], tls_paths['rand'])

    private_key = check_and_create_private_key(base_path)

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    if security_credentials:
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        public_key = os.path.join(tls_paths['mount_dir'], 'publicKey.pem')
        create_public_key(private_key, public_key)

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    client_info = get_client_info(config)
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    create_ca_conf(certificate_config, common_name, tls_paths['mount_dir'], private_key, current_time, region, fs_id,
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                   security_credentials, ap_id, client_info)
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    create_certificate_signing_request(certificate_config, private_key, certificate_signing_request)

    not_before = get_certificate_timestamp(current_time, minutes=-NOT_BEFORE_MINS)
    not_after = get_certificate_timestamp(current_time, hours=NOT_AFTER_HOURS)

    cmd = 'openssl ca -startdate %s -enddate %s -selfsign -batch -notext -config %s -in %s -out %s' % \
          (not_before, not_after, certificate_config, certificate_signing_request, certificate)
    subprocess_call(cmd, 'Failed to create self-signed client-side certificate')
    return current_time.strftime(CERT_DATETIME_FORMAT)


def get_private_key_path():
    """Wrapped for mocking purposes in unit tests"""
    return PRIVATE_KEY_FILE


def check_and_create_private_key(base_path=STATE_FILE_DIR):
    # Creating RSA private keys is slow, so we will create one private key and allow mounts to share it.
    # This means, however, that we have to include a locking mechanism to ensure that the private key is
    # atomically created, as mounts occurring in parallel may try to create the key simultaneously.
    key = get_private_key_path()

    @contextmanager
    def open_lock_file():
        lock_file = os.path.join(base_path, 'efs-utils-lock')
        f = os.open(lock_file, os.O_CREAT | os.O_DSYNC | os.O_EXCL | os.O_RDWR)
        try:
            lock_file_contents = 'PID: %s' % os.getpid()
            os.write(f, lock_file_contents.encode('utf-8'))
            yield f
        finally:
            os.close(f)
            os.remove(lock_file)

    def do_with_lock(function):
        while True:
            try:
                with open_lock_file():
                    return function()
            except OSError as e:
                if e.errno == errno.EEXIST:
                    logging.info('Failed to take out private key creation lock, sleeping 50 ms')
                    time.sleep(0.05)
                else:
                    raise

    def generate_key():
        if os.path.isfile(key):
            return

        cmd = 'openssl genpkey -algorithm RSA -out %s -pkeyopt rsa_keygen_bits:3072' % key
        subprocess_call(cmd, 'Failed to create private key')
        read_only_mode = 0o400
        os.chmod(key, read_only_mode)

    do_with_lock(generate_key)
    return key


def create_certificate_signing_request(config_path, private_key, csr_path):
    cmd = 'openssl req -new -config %s -key %s -out %s' % (config_path, private_key, csr_path)
    subprocess_call(cmd, 'Failed to create certificate signing request (csr)')


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def create_ca_conf(config_path, common_name, directory, private_key, date,
                   region, fs_id, security_credentials, ap_id, client_info):
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    """Populate ca/req configuration file with fresh configurations at every mount since SigV4 signature can change"""
    public_key_path = os.path.join(directory, 'publicKey.pem')
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    ca_extension_body = ca_extension_builder(ap_id, security_credentials, fs_id, client_info)
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    efs_client_auth_body = efs_client_auth_builder(public_key_path, security_credentials['AccessKeyId'],
                                                   security_credentials['SecretAccessKey'], date, region, fs_id,
                                                   security_credentials['Token']) if security_credentials else ''
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    efs_client_info_body = efs_client_info_builder(client_info) if client_info else ''
    full_config_body = CA_CONFIG_BODY % (directory, private_key, common_name, ca_extension_body,
                                         efs_client_auth_body, efs_client_info_body)
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    with open(config_path, 'w') as f:
        f.write(full_config_body)

    return full_config_body


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def ca_extension_builder(ap_id, security_credentials, fs_id, client_info):
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    ca_extension_str = '[ v3_ca ]\nsubjectKeyIdentifier = hash'
    if ap_id:
        ca_extension_str += '\n1.3.6.1.4.1.4843.7.1 = ASN1:UTF8String:' + ap_id
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    if security_credentials:
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        ca_extension_str += '\n1.3.6.1.4.1.4843.7.2 = ASN1:SEQUENCE:efs_client_auth'
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    ca_extension_str += '\n1.3.6.1.4.1.4843.7.3 = ASN1:UTF8String:' + fs_id
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    if client_info:
        ca_extension_str += '\n1.3.6.1.4.1.4843.7.4 = ASN1:SEQUENCE:efs_client_info'

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    return ca_extension_str


def efs_client_auth_builder(public_key_path, access_key_id, secret_access_key, date, region, fs_id, session_token=None):
    public_key_hash = get_public_key_sha1(public_key_path)
    canonical_request = create_canonical_request(public_key_hash, date, access_key_id, region, fs_id, session_token)
    string_to_sign = create_string_to_sign(canonical_request, date, region)
    signature = calculate_signature(string_to_sign, date, secret_access_key, region)
    efs_client_auth_str = '[ efs_client_auth ]'
    efs_client_auth_str += '\naccessKeyId = UTF8String:' + access_key_id
    efs_client_auth_str += '\nsignature = OCTETSTRING:' + signature
    efs_client_auth_str += '\nsigv4DateTime = UTCTIME:' + date.strftime(CERT_DATETIME_FORMAT)

    if session_token:
        efs_client_auth_str += '\nsessionToken = EXPLICIT:0,UTF8String:' + session_token

    return efs_client_auth_str


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def efs_client_info_builder(client_info):
    efs_client_info_str = '[ efs_client_info ]'
    for key, value in client_info.items():
        efs_client_info_str += '\n%s = UTF8String: %s' % (key, value)
    return efs_client_info_str


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def create_public_key(private_key, public_key):
    cmd = 'openssl rsa -in %s -outform PEM -pubout -out %s' % (private_key, public_key)
    subprocess_call(cmd, 'Failed to create public key')


def subprocess_call(cmd, error_message):
    """Helper method to run shell openssl command and to handle response error messages"""
    process = subprocess.Popen(cmd.split(), stdout=subprocess.PIPE, stderr=subprocess.PIPE, close_fds=True)
    (output, err) = process.communicate()
    rc = process.poll()
    if rc != 0:
        logging.error('Command %s failed, rc=%s, stdout="%s", stderr="%s"' % (cmd, rc, output, err))
        fatal_error(error_message, error_message)
    else:
        return output, err


def ca_dirs_check(config, database_dir, certs_dir):
    """Check if mount's database and certs directories exist and if not, create directories (also create all intermediate
    directories if they don't exist)."""
    if not os.path.exists(database_dir):
        create_required_directory(config, database_dir)
    if not os.path.exists(certs_dir):
        create_required_directory(config, certs_dir)


def ca_supporting_files_check(index_path, index_attr_path, serial_path, rand_path):
    """Recreate all supporting openssl ca and req files if they're not present in their respective directories"""
    if not os.path.isfile(index_path):
        open(index_path, 'w').close()
    if not os.path.isfile(index_attr_path):
        with open(index_attr_path, 'w+') as f:
            f.write('unique_subject = no')
    if not os.path.isfile(serial_path):
        with open(serial_path, 'w+') as f:
            f.write('00')
    if not os.path.isfile(rand_path):
        open(rand_path, 'w').close()


def get_certificate_timestamp(current_time, **kwargs):
    updated_time = current_time + timedelta(**kwargs)
    return updated_time.strftime(CERT_DATETIME_FORMAT)


def get_utc_now():
    """
    Wrapped for patching purposes in unit tests
    """
    return datetime.utcnow()


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def assert_root():
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    if os.geteuid() != 0:
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        sys.stderr.write('only root can run mount.efs\n')
        sys.exit(1)


def read_config(config_file=CONFIG_FILE):
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    try:
        p = ConfigParser.SafeConfigParser()
    except AttributeError:
        p = ConfigParser()
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    p.read(config_file)
    return p


def bootstrap_logging(config, log_dir=LOG_DIR):
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    raw_level = config.get(CONFIG_SECTION, 'logging_level')
    levels = {
        'debug': logging.DEBUG,
        'info': logging.INFO,
        'warning': logging.WARNING,
        'error': logging.ERROR,
        'critical': logging.CRITICAL
    }
    level = levels.get(raw_level.lower())
    level_error = False

    if not level:
        # delay logging error about malformed log level until after logging is configured
        level_error = True
        level = logging.INFO

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    max_bytes = config.getint(CONFIG_SECTION, 'logging_max_bytes')
    file_count = config.getint(CONFIG_SECTION, 'logging_file_count')

    handler = RotatingFileHandler(os.path.join(log_dir, LOG_FILE), maxBytes=max_bytes, backupCount=file_count)
    handler.setFormatter(logging.Formatter(fmt='%(asctime)s - %(levelname)s - %(message)s'))

    logger = logging.getLogger()
    logger.setLevel(level)
    logger.addHandler(handler)

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    if level_error:
        logging.error('Malformed logging level "%s", setting logging level to %s', raw_level, level)

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def get_dns_name(config, fs_id):
    def _validate_replacement_field_count(format_str, expected_ct):
        if format_str.count('{') != expected_ct or format_str.count('}') != expected_ct:
            raise ValueError('DNS name format has an incorrect number of replacement fields')

    dns_name_format = config.get(CONFIG_SECTION, 'dns_name_format')

    if '{fs_id}' not in dns_name_format:
        raise ValueError('DNS name format must include {fs_id}')

    format_args = {'fs_id': fs_id}

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    expected_replacement_field_ct = 1

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    if '{region}' in dns_name_format:
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        expected_replacement_field_ct += 1
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        format_args['region'] = get_target_region(config)
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    if '{dns_name_suffix}' in dns_name_format:
        expected_replacement_field_ct += 1
        config_section = CONFIG_SECTION
        region = format_args.get('region')

        if region:
            region_specific_config_section = '%s.%s' % (CONFIG_SECTION, region)
            if config.has_section(region_specific_config_section):
                config_section = region_specific_config_section

        format_args['dns_name_suffix'] = config.get(config_section, 'dns_name_suffix')

        logging.debug("Using dns_name_suffix %s in config section [%s]", format_args.get('dns_name_suffix'), config_section)

    _validate_replacement_field_count(dns_name_format, expected_replacement_field_ct)
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    dns_name = dns_name_format.format(**format_args)

    try:
        socket.gethostbyname(dns_name)
    except socket.gaierror:
        fatal_error('Failed to resolve "%s" - check that your file system ID is correct.\nSee %s for more detail.'
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                    % (dns_name, 'https://docs.aws.amazon.com/console/efs/mount-dns-name'),
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                    'Failed to resolve "%s"' % dns_name)

    return dns_name


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def tls_paths_dictionary(mount_name, base_path=STATE_FILE_DIR):
    tls_dict = {
        'mount_dir': os.path.join(base_path, mount_name),
        # every mount will have its own ca mode assets due to lack of multi-threading support in openssl
        'database_dir': os.path.join(base_path, mount_name, 'database'),
        'certs_dir': os.path.join(base_path, mount_name, 'certs'),
        'index': os.path.join(base_path, mount_name, 'database/index.txt'),
        'index_attr': os.path.join(base_path, mount_name, 'database/index.txt.attr'),
        'serial': os.path.join(base_path, mount_name, 'database/serial'),
        'rand': os.path.join(base_path, mount_name, 'database/.rand')
    }

    return tls_dict


def get_public_key_sha1(public_key):
    # truncating public key to remove the header and footer '-----(BEGIN|END) PUBLIC KEY-----'
    with open(public_key, 'r') as f:
        lines = f.readlines()
        lines = lines[1:-1]

    key = ''.join(lines)
    key = bytearray(base64.b64decode(key))

    # Parse the public key to pull out the actual key material by looking for the key BIT STRING
    # Example:
    #     0:d=0  hl=4 l= 418 cons: SEQUENCE
    #     4:d=1  hl=2 l=  13 cons: SEQUENCE
    #     6:d=2  hl=2 l=   9 prim: OBJECT            :rsaEncryption
    #    17:d=2  hl=2 l=   0 prim: NULL
    #    19:d=1  hl=4 l= 399 prim: BIT STRING
    cmd = 'openssl asn1parse -inform PEM -in %s' % public_key
    output, err = subprocess_call(cmd, 'Unable to ASN1 parse public key file, %s, correctly' % public_key)

    key_line = ''
    for line in output.splitlines():
        if 'BIT STRING' in line.decode('utf-8'):
            key_line = line.decode('utf-8')

    if not key_line:
        err_msg = 'Public key file, %s, is incorrectly formatted' % public_key
        fatal_error(err_msg, err_msg)

    key_line = key_line.replace(' ', '')

    # DER encoding TLV (Tag, Length, Value)
    # - the first octet (byte) is the tag (type)
    # - the next octets are the length - "definite form"
    #   - the first octet always has the high order bit (8) set to 1
    #   - the remaining 127 bits are used to encode the number of octets that follow
    #   - the following octets encode, as big-endian, the length (which may be 0) as a number of octets
    # - the remaining octets are the "value" aka content
    #
    # For a BIT STRING, the first octet of the value is used to signify the number of unused bits that exist in the last
    # content byte. Note that this is explicitly excluded from the SubjectKeyIdentifier hash, per
    # https://tools.ietf.org/html/rfc5280#section-4.2.1.2
    #
    # Example:
    #   0382018f00...<subjectPublicKey>
    #   - 03 - BIT STRING tag
    #   - 82 - 2 length octets to follow (ignore high order bit)
    #   - 018f - length of 399
    #   - 00 - no unused bits in the last content byte
    offset = int(key_line.split(':')[0])
    key = key[offset:]

    num_length_octets = key[1] & 0b01111111

    # Exclude the tag (1), length (1 + num_length_octets), and number of unused bits (1)
    offset = 1 + 1 + num_length_octets + 1
    key = key[offset:]

    sha1 = hashlib.sha1()
    sha1.update(key)

    return sha1.hexdigest()


def create_canonical_request(public_key_hash, date, access_key, region, fs_id, session_token=None):
    """
    Create a Canonical Request - https://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html
    """
    formatted_datetime = date.strftime(SIGV4_DATETIME_FORMAT)
    credential = quote_plus(access_key + '/' + get_credential_scope(date, region))

    request = HTTP_REQUEST_METHOD + '\n'
    request += CANONICAL_URI + '\n'
    request += create_canonical_query_string(public_key_hash, credential, formatted_datetime, session_token) + '\n'
    request += CANONICAL_HEADERS % fs_id + '\n'
    request += SIGNED_HEADERS + '\n'

    sha256 = hashlib.sha256()
    sha256.update(REQUEST_PAYLOAD.encode())
    request += sha256.hexdigest()

    return request


def create_canonical_query_string(public_key_hash, credential, formatted_datetime, session_token=None):
    canonical_query_params = {
        'Action': 'Connect',
        # Public key hash is included in canonical request to tie the signature to a specific key pair to avoid replay attacks
        'PublicKeyHash': quote_plus(public_key_hash),
        'X-Amz-Algorithm': ALGORITHM,
        'X-Amz-Credential': credential,
        'X-Amz-Date': quote_plus(formatted_datetime),
        'X-Amz-Expires': 86400,
        'X-Amz-SignedHeaders': SIGNED_HEADERS,
    }

    if session_token:
        canonical_query_params['X-Amz-Security-Token'] = quote_plus(session_token)

    # Cannot use urllib.urlencode because it replaces the %s's
    return '&'.join(['%s=%s' % (k, v) for k, v in sorted(canonical_query_params.items())])


def create_string_to_sign(canonical_request, date, region):
    """
    Create a String to Sign - https://docs.aws.amazon.com/general/latest/gr/sigv4-create-string-to-sign.html
    """
    string_to_sign = ALGORITHM + '\n'
    string_to_sign += date.strftime(SIGV4_DATETIME_FORMAT) + '\n'
    string_to_sign += get_credential_scope(date, region) + '\n'

    sha256 = hashlib.sha256()
    sha256.update(canonical_request.encode())
    string_to_sign += sha256.hexdigest()

    return string_to_sign


def calculate_signature(string_to_sign, date, secret_access_key, region):
    """
    Calculate the Signature - https://docs.aws.amazon.com/general/latest/gr/sigv4-calculate-signature.html
    """
    def _sign(key, msg):
        return hmac.new(key, msg.encode('utf-8'), hashlib.sha256)

    key_date = _sign(('AWS4' + secret_access_key).encode('utf-8'), date.strftime(DATE_ONLY_FORMAT)).digest()
    add_region = _sign(key_date, region).digest()
    add_service = _sign(add_region, SERVICE).digest()
    signing_key = _sign(add_service, 'aws4_request').digest()

    return _sign(signing_key, string_to_sign).hexdigest()


def get_credential_scope(date, region):
    return '/'.join([date.strftime(DATE_ONLY_FORMAT), region, SERVICE, AWS4_REQUEST])


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def match_device(config, device):
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    """Return the EFS id and the remote path to mount"""
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    try:
        remote, path = device.split(':', 1)
    except ValueError:
        remote = device
        path = '/'

    if FS_ID_RE.match(remote):
        return remote, path

    try:
        primary, secondaries, _ = socket.gethostbyname_ex(remote)
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        hostnames = list(filter(lambda e: e is not None, [primary] + secondaries))
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    except socket.gaierror:
        fatal_error(
            'Failed to resolve "%s" - check that the specified DNS name is a CNAME record resolving to a valid EFS DNS '
            'name' % remote,
            'Failed to resolve "%s"' % remote
        )

    if not hostnames:
        fatal_error(
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            'The specified domain name "%s" did not resolve to an EFS mount target' % remote
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        )

    for hostname in hostnames:
        efs_fqdn_match = EFS_FQDN_RE.match(hostname)
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        if efs_fqdn_match:
            fs_id = efs_fqdn_match.group('fs_id')
            expected_dns_name = get_dns_name(config, fs_id)
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            # check that the DNS name of the mount target matches exactly the DNS name the CNAME resolves to
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            if hostname == expected_dns_name:
                return fs_id, path
    else:
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        fatal_error('The specified CNAME "%s" did not resolve to a valid DNS name for an EFS mount target. '
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                    'Please refer to the EFS documentation for mounting with DNS names for examples: %s'
                    % (remote, 'https://docs.aws.amazon.com/efs/latest/ug/mounting-fs-mount-cmd-dns-name.html'))
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def mount_tls(config, init_system, dns_name, path, fs_id, mountpoint, options):
    with bootstrap_tls(config, init_system, dns_name, fs_id, mountpoint, options) as tunnel_proc:
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        mount_completed = threading.Event()
        t = threading.Thread(target=poll_tunnel_process, args=(tunnel_proc, fs_id, mount_completed))
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        t.daemon = True
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        t.start()
        mount_nfs(dns_name, path, mountpoint, options)
        mount_completed.set()
        t.join()


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def check_unsupported_options(options):
    for unsupported_option in UNSUPPORTED_OPTIONS:
        if unsupported_option in options:
            warn_message = 'The "%s" option is not supported and has been ignored, as amazon-efs-utils relies on a built-in ' \
                           'trust store.' % unsupported_option
            sys.stderr.write('WARN: %s\n' % warn_message)
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            logging.warning(warn_message)
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            del options[unsupported_option]


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