transaction.py: fix script_GetOp for malformed scripts

related fyookball/electrum#829

electrum/tests/test_transaction.py

@@ -307,6 +307,12 @@ class TestTransaction(SequentialTestCase):
         txid = '9b9f39e314662a7433aadaa5c94a2f1e24c7e7bf55fc9e1f83abd72be933eb95'
         self._run_naive_tests_on_tx(raw_tx, txid)
 
+    # see https://bitcoin.stackexchange.com/questions/38006/txout-script-criteria-scriptpubkey-critieria
+    def test_txid_invalid_op_return(self):
+        raw_tx = '01000000019ac03d5ae6a875d970128ef9086cef276a1919684a6988023cc7254691d97e6d010000006b4830450221009d41dc793ba24e65f571473d40b299b6459087cea1509f0d381740b1ac863cb6022039c425906fcaf51b2b84d8092569fb3213de43abaff2180e2a799d4fcb4dd0aa012102d5ede09a8ae667d0f855ef90325e27f6ce35bbe60a1e6e87af7f5b3c652140fdffffffff080100000000000000010101000000000000000202010100000000000000014c0100000000000000034c02010100000000000000014d0100000000000000044dffff010100000000000000014e0100000000000000064effffffff0100000000'
+        txid = 'ebc9fa1196a59e192352d76c0f6e73167046b9d37b8302b6bb6968dfd279b767'
+        self._run_naive_tests_on_tx(raw_tx, txid)
+
 
 # these transactions are from Bitcoin Core unit tests --->
 # https://github.com/bitcoin/bitcoin/blob/11376b5583a283772c82f6d32d0007cdbf5b8ef0/src/test/data/tx_valid.json

electrum/transaction.py

@@ -59,6 +59,10 @@ class NotRecognizedRedeemScript(Exception):
     pass
 
 
+class MalformedBitcoinScript(Exception):
+    pass
+
+
 TxOutput = NamedTuple("TxOutput", [('type', int), ('address', str), ('value', Union[int, str])])
 # ^ value is str when the output is set to max: '!'
 
@@ -263,13 +267,16 @@ def script_GetOp(_bytes : bytes):
         if opcode <= opcodes.OP_PUSHDATA4:
             nSize = opcode
             if opcode == opcodes.OP_PUSHDATA1:
-                nSize = _bytes[i]
+                try: nSize = _bytes[i]
+                except IndexError: raise MalformedBitcoinScript()
                 i += 1
             elif opcode == opcodes.OP_PUSHDATA2:
-                (nSize,) = struct.unpack_from('<H', _bytes, i)
+                try: (nSize,) = struct.unpack_from('<H', _bytes, i)
+                except struct.error: raise MalformedBitcoinScript()
                 i += 2
             elif opcode == opcodes.OP_PUSHDATA4:
-                (nSize,) = struct.unpack_from('<I', _bytes, i)
+                try: (nSize,) = struct.unpack_from('<I', _bytes, i)
+                except struct.error: raise MalformedBitcoinScript()
                 i += 4
             vch = _bytes[i:i + nSize]
             i += nSize
@@ -281,21 +288,11 @@ def script_GetOpName(opcode):
     return (opcodes.whatis(opcode)).replace("OP_", "")
 
 
-def decode_script(bytes):
-    result = ''
-    for (opcode, vch, i) in script_GetOp(bytes):
-        if len(result) > 0: result += " "
-        if opcode <= opcodes.OP_PUSHDATA4:
-            result += "%d:"%(opcode,)
-            result += short_hex(vch)
-        else:
-            result += script_GetOpName(opcode)
-    return result
-
-
 def match_decoded(decoded, to_match):
+    if decoded is None:
+        return False
     if len(decoded) != len(to_match):
-        return False;
+        return False
     for i in range(len(decoded)):
         if to_match[i] == opcodes.OP_PUSHDATA4 and decoded[i][0] <= opcodes.OP_PUSHDATA4 and decoded[i][0]>0:
             continue  # Opcodes below OP_PUSHDATA4 all just push data onto stack, and are equivalent.
@@ -413,7 +410,10 @@ def parse_scriptSig(d, _bytes):
 
 
 def parse_redeemScript_multisig(redeem_script: bytes):
-    dec2 = [ x for x in script_GetOp(redeem_script) ]
+    try:
+        dec2 = [ x for x in script_GetOp(redeem_script) ]
+    except MalformedBitcoinScript:
+        raise NotRecognizedRedeemScript()
     try:
         m = dec2[0][0] - opcodes.OP_1 + 1
         n = dec2[-2][0] - opcodes.OP_1 + 1
@@ -434,7 +434,10 @@ def parse_redeemScript_multisig(redeem_script: bytes):
 
 
 def get_address_from_output_script(_bytes, *, net=None):
-    decoded = [x for x in script_GetOp(_bytes)]
+    try:
+        decoded = [x for x in script_GetOp(_bytes)]
+    except MalformedBitcoinScript:
+        decoded = None
 
     # The Genesis Block, self-payments, and pay-by-IP-address payments look like:
     # 65 BYTES:... CHECKSIG