add cardano output address validation

src/apps/cardano/address.py

@@ -1,3 +1,4 @@
+from trezor import log
 from trezor.crypto import base58, crc, hashlib
 
 from apps.cardano import cbor
@@ -5,6 +6,14 @@ from apps.common import HARDENED
 from apps.common.seed import remove_ed25519_prefix
 
 
+def _encode_address_raw(address_data_encoded):
+    return base58.encode(
+        cbor.encode(
+            [cbor.Tagged(24, address_data_encoded), crc.crc32(address_data_encoded)]
+        )
+    )
+
+
 def derive_address_and_node(keychain, path: list):
     node = keychain.derive(path)
 
@@ -16,12 +25,31 @@ def derive_address_and_node(keychain, path: list):
     address_data = [address_root, address_attributes, address_type]
     address_data_encoded = cbor.encode(address_data)
 
-    address = base58.encode(
-        cbor.encode(
-            [cbor.Tagged(24, address_data_encoded), crc.crc32(address_data_encoded)]
-        )
-    )
-    return (address, node)
+    return (_encode_address_raw(address_data_encoded), node)
+
+
+def is_safe_output_address(address) -> bool:
+    """
+    Determines whether it is safe to include the address as-is as
+    a tx output, preventing unintended side effects (e.g. CBOR injection)
+    """
+    try:
+        address_hex = base58.decode(address)
+        address_unpacked = cbor.decode(address_hex)
+    except ValueError as e:
+        if __debug__:
+            log.exception(__name__, e)
+        return False
+
+    if not isinstance(address_unpacked, list) or len(address_unpacked) != 2:
+        return False
+
+    address_data_encoded = address_unpacked[0]
+
+    if not isinstance(address_data_encoded, bytes):
+        return False
+
+    return _encode_address_raw(address_data_encoded) == address
 
 
 def validate_full_path(path: list) -> bool:

src/apps/cardano/sign_tx.py

@@ -8,7 +8,11 @@ from trezor.messages.CardanoTxRequest import CardanoTxRequest
 from trezor.messages.MessageType import CardanoTxAck
 
 from apps.cardano import cbor, seed
-from apps.cardano.address import derive_address_and_node, validate_full_path
+from apps.cardano.address import (
+    derive_address_and_node,
+    is_safe_output_address,
+    validate_full_path,
+)
 from apps.cardano.layout import confirm_sending, confirm_transaction, progress
 from apps.common.paths import validate_path
 from apps.common.seed import remove_ed25519_prefix
@@ -184,6 +188,8 @@ class Transaction:
                     raise wire.ProcessError(
                         "Each output must have address or address_n field!"
                     )
+                if not is_safe_output_address(output.address):
+                    raise wire.ProcessError("Invalid output address!")
 
                 outgoing_coins.append(output.amount)
                 output_addresses.append(output.address)