lnpeer: cooperative close: verify scriptpubkey matches templates

electrum/lnpeer.py

@@ -25,7 +25,8 @@ from . import ecc
 from .ecc import sig_string_from_r_and_s, get_r_and_s_from_sig_string, der_sig_from_sig_string
 from . import constants
 from .util import bh2u, bfh, log_exceptions, ignore_exceptions, chunks, SilentTaskGroup
-from .transaction import Transaction, TxOutput, PartialTxOutput
+from . import transaction
+from .transaction import Transaction, TxOutput, PartialTxOutput, match_script_against_template
 from .logging import Logger
 from .lnonion import (new_onion_packet, decode_onion_error, OnionFailureCode, calc_hops_data_for_payment,
                       process_onion_packet, OnionPacket, construct_onion_error, OnionRoutingFailureMessage,
@@ -1357,9 +1358,12 @@ class Peer(Logger):
 
     @log_exceptions
     async def on_shutdown(self, payload):
-        # length of scripts allowed in BOLT-02
-        if int.from_bytes(payload['len'], 'big') not in (3+20+2, 2+20+1, 2+20, 2+32):
-            raise Exception('scriptpubkey length in received shutdown message invalid: ' + str(payload['len']))
+        their_scriptpubkey = payload['scriptpubkey']
+        # BOLT-02 restrict the scriptpubkey to some templates:
+        if not (match_script_against_template(their_scriptpubkey, transaction.SCRIPTPUBKEY_TEMPLATE_WITNESS_V0)
+                or match_script_against_template(their_scriptpubkey, transaction.SCRIPTPUBKEY_TEMPLATE_P2SH)
+                or match_script_against_template(their_scriptpubkey, transaction.SCRIPTPUBKEY_TEMPLATE_P2PKH)):
+            raise Exception(f'scriptpubkey in received shutdown message does not conform to any template: {their_scriptpubkey.hex()}')
         chan_id = payload['channel_id']
         if chan_id in self.shutdown_received:
             self.shutdown_received[chan_id].set_result(payload)

electrum/transaction.py

@@ -390,20 +390,32 @@ class OPPushDataGeneric:
 
 
 OPPushDataPubkey = OPPushDataGeneric(lambda x: x in (33, 65))
-# note that this does not include x_pubkeys !
 
+SCRIPTPUBKEY_TEMPLATE_P2PKH = [opcodes.OP_DUP, opcodes.OP_HASH160,
+                               OPPushDataGeneric(lambda x: x == 20),
+                               opcodes.OP_EQUALVERIFY, opcodes.OP_CHECKSIG]
+SCRIPTPUBKEY_TEMPLATE_P2SH = [opcodes.OP_HASH160, OPPushDataGeneric(lambda x: x == 20), opcodes.OP_EQUAL]
+SCRIPTPUBKEY_TEMPLATE_WITNESS_V0 = [opcodes.OP_0, OPPushDataGeneric(lambda x: x in (20, 32))]
 
-def match_decoded(decoded, to_match):
-    if decoded is None:
+
+def match_script_against_template(script, template) -> bool:
+    """Returns whether 'script' matches 'template'."""
+    if script is None:
         return False
-    if len(decoded) != len(to_match):
+    # optionally decode script now:
+    if isinstance(script, (bytes, bytearray)):
+        try:
+            script = [x for x in script_GetOp(script)]
+        except MalformedBitcoinScript:
+            return False
+    if len(script) != len(template):
         return False
-    for i in range(len(decoded)):
-        to_match_item = to_match[i]
-        decoded_item = decoded[i]
-        if OPPushDataGeneric.is_instance(to_match_item) and to_match_item.check_data_len(decoded_item[0]):
+    for i in range(len(script)):
+        template_item = template[i]
+        script_item = script[i]
+        if OPPushDataGeneric.is_instance(template_item) and template_item.check_data_len(script_item[0]):
             continue
-        if to_match_item != decoded_item[0]:
+        if template_item != script_item[0]:
             return False
     return True
 
@@ -412,28 +424,25 @@ def get_address_from_output_script(_bytes: bytes, *, net=None) -> Optional[str]:
     try:
         decoded = [x for x in script_GetOp(_bytes)]
     except MalformedBitcoinScript:
-        decoded = None
+        return None
 
     # p2pkh
-    match = [opcodes.OP_DUP, opcodes.OP_HASH160, OPPushDataGeneric(lambda x: x == 20), opcodes.OP_EQUALVERIFY, opcodes.OP_CHECKSIG]
-    if match_decoded(decoded, match):
+    if match_script_against_template(decoded, SCRIPTPUBKEY_TEMPLATE_P2PKH):
         return hash160_to_p2pkh(decoded[2][1], net=net)
 
     # p2sh
-    match = [opcodes.OP_HASH160, OPPushDataGeneric(lambda x: x == 20), opcodes.OP_EQUAL]
-    if match_decoded(decoded, match):
+    if match_script_against_template(decoded, SCRIPTPUBKEY_TEMPLATE_P2SH):
         return hash160_to_p2sh(decoded[1][1], net=net)
 
     # segwit address (version 0)
-    match = [opcodes.OP_0, OPPushDataGeneric(lambda x: x in (20, 32))]
-    if match_decoded(decoded, match):
+    if match_script_against_template(decoded, SCRIPTPUBKEY_TEMPLATE_WITNESS_V0):
         return hash_to_segwit_addr(decoded[1][1], witver=0, net=net)
 
     # segwit address (version 1-16)
     future_witness_versions = list(range(opcodes.OP_1, opcodes.OP_16 + 1))
     for witver, opcode in enumerate(future_witness_versions, start=1):
         match = [opcode, OPPushDataGeneric(lambda x: 2 <= x <= 40)]
-        if match_decoded(decoded, match):
+        if match_script_against_template(decoded, match):
             return hash_to_segwit_addr(decoded[1][1], witver=witver, net=net)
 
     return None
@@ -1348,14 +1357,13 @@ class PartialTxInput(TxInput, PSBTSection):
                 except MalformedBitcoinScript:
                     decoded = None
                 # witness version 0
-                match = [opcodes.OP_0, OPPushDataGeneric(lambda x: x in (20, 32))]
-                if match_decoded(decoded, match):
+                if match_script_against_template(decoded, SCRIPTPUBKEY_TEMPLATE_WITNESS_V0):
                     return True
                 # witness version 1-16
                 future_witness_versions = list(range(opcodes.OP_1, opcodes.OP_16 + 1))
                 for witver, opcode in enumerate(future_witness_versions, start=1):
                     match = [opcode, OPPushDataGeneric(lambda x: 2 <= x <= 40)]
-                    if match_decoded(decoded, match):
+                    if match_script_against_template(decoded, match):
                         return True
                 return False