Be stricter accepting add_peer requests

- rate-limit onion add_peer requests
- for clearnet peers only accept if the peer resolves to the
  source address

server/controller.py

@@ -49,7 +49,6 @@ class Controller(util.LoggedClass):
         self.executor = ThreadPoolExecutor()
         self.loop.set_default_executor(self.executor)
         self.start_time = time.time()
-        self.next_add_peer_time = self.start_time
         self.coin = env.coin
         self.daemon = Daemon(env.coin.daemon_urls(env.daemon_url))
         self.bp = BlockProcessor(env, self, self.daemon)
@@ -136,15 +135,6 @@ class Controller(util.LoggedClass):
     def is_deprioritized(self, session):
         return self.session_priority(session) > self.BANDS
 
-    def permit_add_peer(self):
-        '''To prevent lots of add_peer requests filling up the peer
-        table, accept only one per random time interval.'''
-        now = time.time()
-        if now < self.next_add_peer_time:
-            return False
-        self.next_add_peer_time = now + random.randrange(0, 1800)
-        return True
-
     async def run_in_executor(self, func, *args):
         '''Wait whilst running func in the executor.'''
         return await self.loop.run_in_executor(None, func, *args)

server/peers.py

@@ -14,6 +14,7 @@ import ssl
 import time
 from collections import defaultdict, Counter
 from functools import partial
+from socket import SOCK_STREAM
 
 from lib.jsonrpc import JSONSession
 from lib.peer import Peer
@@ -221,6 +222,7 @@ class PeerManager(util.LoggedClass):
         # any other peers with the same host name or IP address.
         self.peers = set()
         self.onion_peers = []
+        self.permit_onion_peer_time = time.time()
         self.last_tor_retry_time = 0
         self.tor_proxy = SocksProxy(env.tor_proxy_host, env.tor_proxy_port,
                                     loop=self.loop)
@@ -302,15 +304,43 @@ class PeerManager(util.LoggedClass):
         if retry:
             self.retry_event.set()
 
-    def on_add_peer(self, features, source):
-        '''Add peers from an incoming connection.'''
+    def permit_new_onion_peer(self):
+        '''Accept a new onion peer only once per random time interval.'''
+        now = time.time()
+        if now < self.permit_onion_peer_time:
+            return False
+        self.permit_onion_peer_time = now + random.randrange(0, 1200)
+        return True
+
+    async def on_add_peer(self, features, source_info):
+        '''Add a peer (but only if the peer resolves to the source).'''
+        if not source_info:
+            return False
+        source = source_info[0]
         peers = Peer.peers_from_features(features, source)
-        if peers:
-            hosts = [peer.host for peer in peers]
-            self.log_info('add_peer request from {} for {}'
-                          .format(source, ', '.join(hosts)))
-            self.add_peers(peers, check_ports=True)
-        return bool(peers)
+        if not peers:
+            return False
+
+        # Just look at the first peer, require it
+        peer = peers[0]
+        host = peer.host
+        if peer.is_tor:
+            permit = self.permit_new_onion_peer()
+            reason = 'rate limiting'
+        else:
+            infos = await self.loop.getaddrinfo(host, 80, type=SOCK_STREAM)
+            permit = any(source == info[-1][0] for info in infos)
+            reason = 'source-destination mismatch'
+
+        if permit:
+            self.log_info('accepted add_peer request from {} for {}'
+                          .format(source, host))
+            self.add_peers([peer], check_ports=True)
+        else:
+            self.log_warning('rejected add_peer request from {} for {} ({})'
+                             .format(source, host, reason))
+
+        return permit
 
     def on_peers_subscribe(self, is_tor):
         '''Returns the server peers as a list of (ip, host, details) tuples.

server/session.py

@@ -193,14 +193,10 @@ class ElectrumX(SessionBase):
         self.subscribe_height = True
         return self.height()
 
-    def add_peer(self, features):
-        '''Add a peer.'''
-        if not self.controller.permit_add_peer():
-            return False
+    async def add_peer(self, features):
+        '''Add a peer (but only if the peer resolves to the source).'''
         peer_mgr = self.controller.peer_mgr
-        peer_info = self.peer_info()
-        source = peer_info[0] if peer_info else 'unknown'
-        return peer_mgr.on_add_peer(features, source)
+        return await peer_mgr.on_add_peer(features, self.peer_info())
 
     def peers_subscribe(self):
         '''Return the server peers as a list of (ip, host, details) tuples.'''