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# SPDX-License-Identifier: AGPL-3.0-or-later
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"""
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Method ``link_token``
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---------------------
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The ``link_token`` method evaluates a request as :py:obj:`suspicious
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<is_suspicious>` if the URL ``/client<token>.css`` is not requested by the
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client. By adding a random component (the token) in the URL, a bot can not send
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a ping by request a static URL.
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.. note::
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This method requires a redis DB and needs a HTTP X-Forwarded-For_ header.
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To get in use of this method a flask URL route needs to be added:
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.. code:: python
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@app.route('/client<token>.css', methods=['GET', 'POST'])
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def client_token(token=None):
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link_token.ping(request, token)
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return Response('', mimetype='text/css')
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And in the HTML template from flask a stylesheet link is needed (the value of
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``link_token`` comes from :py:obj:`get_token`):
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.. code:: html
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<link rel="stylesheet"
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href="{{ url_for('client_token', token=link_token) }}"
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type="text/css" />
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.. _X-Forwarded-For:
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https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Forwarded-For
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"""
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from __future__ import annotations
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from ipaddress import (
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IPv4Network,
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IPv6Network,
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ip_address,
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)
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import string
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import random
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import flask
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from searx import logger
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from searx import redisdb
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from searx.redislib import secret_hash
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from ._helpers import (
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get_network,
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get_real_ip,
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)
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TOKEN_LIVE_TIME = 600
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"""Livetime (sec) of limiter's CSS token."""
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PING_LIVE_TIME = 3600
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"""Livetime (sec) of the ping-key from a client (request)"""
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PING_KEY = 'SearXNG_limiter.ping'
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"""Prefix of all ping-keys generated by :py:obj:`get_ping_key`"""
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TOKEN_KEY = 'SearXNG_limiter.token'
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"""Key for which the current token is stored in the DB"""
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logger = logger.getChild('botdetection.link_token')
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def is_suspicious(network: IPv4Network | IPv6Network, request: flask.Request, renew: bool = False):
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"""Checks whether a valid ping is exists for this (client) network, if not
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this request is rated as *suspicious*. If a valid ping exists and argument
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``renew`` is ``True`` the expire time of this ping is reset to
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:py:obj:`PING_LIVE_TIME`.
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"""
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redis_client = redisdb.client()
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if not redis_client:
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return False
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ping_key = get_ping_key(network, request)
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if not redis_client.get(ping_key):
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logger.info("missing ping (IP: %s) / request: %s", network.compressed, ping_key)
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return True
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if renew:
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redis_client.set(ping_key, 1, ex=PING_LIVE_TIME)
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logger.debug("found ping for (client) network %s -> %s", network.compressed, ping_key)
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return False
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def ping(request: flask.Request, token: str):
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"""This function is called by a request to URL ``/client<token>.css``. If
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``token`` is valid a :py:obj:`PING_KEY` for the client is stored in the DB.
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The expire time of this ping-key is :py:obj:`PING_LIVE_TIME`.
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"""
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from . import redis_client, cfg # pylint: disable=import-outside-toplevel, cyclic-import
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if not redis_client:
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return
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if not token_is_valid(token):
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return
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real_ip = ip_address(get_real_ip(request))
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network = get_network(real_ip, cfg)
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ping_key = get_ping_key(network, request)
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logger.debug("store ping_key for (client) network %s (IP %s) -> %s", network.compressed, real_ip, ping_key)
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redis_client.set(ping_key, 1, ex=PING_LIVE_TIME)
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def get_ping_key(network: IPv4Network | IPv6Network, request: flask.Request) -> str:
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"""Generates a hashed key that fits (more or less) to a *WEB-browser
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session* in a network."""
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return (
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PING_KEY
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+ "["
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+ secret_hash(
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network.compressed + request.headers.get('Accept-Language', '') + request.headers.get('User-Agent', '')
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)
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+ "]"
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)
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def token_is_valid(token) -> bool:
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valid = token == get_token()
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logger.debug("token is valid --> %s", valid)
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return valid
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def get_token() -> str:
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"""Returns current token. If there is no currently active token a new token
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is generated randomly and stored in the redis DB.
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- :py:obj:`TOKEN_LIVE_TIME`
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- :py:obj:`TOKEN_KEY`
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"""
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redis_client = redisdb.client()
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if not redis_client:
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# This function is also called when limiter is inactive / no redis DB
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# (see render function in webapp.py)
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return '12345678'
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token = redis_client.get(TOKEN_KEY)
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if token:
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token = token.decode('UTF-8')
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else:
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token = ''.join(random.choice(string.ascii_lowercase + string.digits) for _ in range(16))
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redis_client.set(TOKEN_KEY, token, ex=TOKEN_LIVE_TIME)
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return token
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