fix(cardano): don't allow duplicate withdrawals

common/tests/fixtures/cardano/sign_tx.failed.json

@@ -555,6 +555,44 @@
         "error_message": "Invalid withdrawal"
       }
     },
+
+    {
+      "description": "Duplicate withdrawal",
+      "parameters": {
+        "protocol_magic": 764824073,
+        "network_id": 1,
+        "fee": 42,
+        "ttl": 10,
+        "certificates": [],
+        "withdrawals": [
+          {
+            "path": "m/1852'/1815'/0'/2/0",
+            "amount": "1000"
+          },
+          {
+            "path": "m/1852'/1815'/0'/2/0",
+            "amount": "2000"
+          }
+        ],
+        "auxiliary_data": null,
+        "inputs": [
+          {
+            "path": "m/1852'/1815'/0'/0/0",
+            "prev_hash": "3b40265111d8bb3c3c608d95b3a0bf83461ace32d79336579a1939b3aad1c0b7",
+            "prev_index": 0
+          }
+        ],
+        "outputs": [
+          {
+            "address": "Ae2tdPwUPEZCanmBz5g2GEwFqKTKpNJcGYPKfDxoNeKZ8bRHr8366kseiK2",
+            "amount": "3003112"
+          }
+        ]
+      },
+      "result": {
+        "error_message": "Duplicate withdrawals"
+      }
+    },
     {
       "description": "Auxiliary data blob is incomplete",
       "parameters": {

core/src/apps/cardano/sign_tx.py

@@ -309,6 +309,7 @@ def _validate_certificates(
 
 
 def _validate_withdrawals(withdrawals: list[CardanoTxWithdrawalType]) -> None:
+    seen_withdrawals = set()
     for withdrawal in withdrawals:
         if not SCHEMA_STAKING_ANY_ACCOUNT.match(withdrawal.path):
             raise INVALID_WITHDRAWAL
@@ -316,6 +317,12 @@ def _validate_withdrawals(withdrawals: list[CardanoTxWithdrawalType]) -> None:
         if not 0 <= withdrawal.amount < LOVELACE_MAX_SUPPLY:
             raise INVALID_WITHDRAWAL
 
+        path_tuple = tuple(withdrawal.path)
+        if path_tuple in seen_withdrawals:
+            raise wire.ProcessError("Duplicate withdrawals")
+        else:
+            seen_withdrawals.add(path_tuple)
+
 
 def _cborize_signed_tx(
     keychain: seed.Keychain, msg: CardanoSignTx