core, legacy: make sure OPRETURN ouput is not marked as change

core/src/apps/wallet/sign_tx/signing.py

@@ -790,6 +790,13 @@ def output_is_change(
     segwit_in: int,
     multifp: multisig.MultisigFingerprint,
 ) -> bool:
+    if o.script_type not in (
+        OutputScriptType.PAYTOADDRESS,
+        OutputScriptType.PAYTOMULTISIG,
+        OutputScriptType.PAYTOWITNESS,
+        OutputScriptType.PAYTOP2SHWITNESS,
+    ):
+        return False
     if o.multisig and not multifp.matches(o.multisig):
         return False
     if output_is_segwit(o) and o.amount > segwit_in:

legacy/firmware/signing.c

@@ -696,6 +696,13 @@ static bool signing_check_output(TxOutputType *txoutput) {
     }
   }
 
+  if ((txoutput->script_type != OutputScriptType_PAYTOADDRESS) &&
+      (txoutput->script_type != OutputScriptType_PAYTOMULTISIG) &&
+      (txoutput->script_type != OutputScriptType_PAYTOWITNESS) &&
+      (txoutput->script_type != OutputScriptType_PAYTOP2SHWITNESS)) {
+    is_change = false;
+  }
+
   if (is_change) {
     if (change_spend == 0) {  // not set
       change_spend = txoutput->amount;