core/sign_tx: If there is a non-multisig input, then change output cannot be multisig.

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

@@ -111,6 +111,8 @@ async def check_tx_fee(tx: SignTx, keychain: seed.Keychain):
 
         if txi.multisig:
             multifp.add(txi.multisig)
+        else:
+            multifp.mismatch = True
 
         if txi.script_type in (
             InputScriptType.SPENDWITNESS,

tests/device_tests/test_msg_signtx_segwit_native.py

@@ -804,3 +804,119 @@ class TestMsgSigntxSegwitNative:
             serialized_tx.hex()
             == "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"
         )
+
+    # Ensure that if there is a non-multisig input, then a multisig output
+    # will not be identified as a change output.
+    def test_multisig_mismatch_inputs_single(self, client):
+        # m/84'/1'/0' for "alcohol woman abuse ..." seed.
+        node_int = deserialize(
+            "Vpub5kFDCYhiYuAzjk7TBQPNFffbexHF7iAd8AVVgHQKUany7e6NQvthgk86d7DfH57DY2dwBK4PyVTDDaS1r2gjkdyJyUYGoV9qNujGSrW9Dpe"
+        )
+
+        # m/84'/1'/0' for "all all ... all" seed.
+        node_ext = deserialize(
+            "Vpub5jR76XyyhBaQXPSRf3PBeY3gF914d9sf7DWFVhMESEQMCdNv35XiVvp8gZsFXAv222VPHLNnAEXxMPG8DPiSuhAXfEydBf55LTLBGHCDzH2"
+        )
+
+        # tb1qpzmgzpcumztvmpu3q27wwdggqav26j9dgks92pvnne2lz9ferxgssmhzlq
+        multisig_in = proto.MultisigRedeemScriptType(
+            nodes=[node_int, node_ext], address_n=[0, 0], signatures=[b"", b""], m=1
+        )
+
+        multisig_out = proto.MultisigRedeemScriptType(
+            nodes=[node_int, node_ext], address_n=[1, 0], signatures=[b"", b""], m=1
+        )
+
+        inp1 = proto.TxInputType(
+            address_n=parse_path("84'/1'/0'/0/0"),
+            amount=12300000,
+            prev_hash=bytes.fromhex(
+                "09144602765ce3dd8f4329445b20e3684e948709c5cdcaf12da3bb079c99448a"
+            ),
+            prev_index=0,
+            script_type=proto.InputScriptType.SPENDWITNESS,
+        )
+
+        inp2 = proto.TxInputType(
+            address_n=parse_path("84'/1'/0'/0/0"),
+            prev_hash=bytes.fromhex(
+                "a345b85759b385c6446055e4c3baa77e8161a65009dc009489b48aa6587ce348"
+            ),
+            prev_index=0,
+            script_type=proto.InputScriptType.SPENDWITNESS,
+            multisig=multisig_in,
+            amount=100,
+        )
+
+        out1 = proto.TxOutputType(
+            address="2N4Q5FhU2497BryFfUgbqkAJE87aKHUhXMp",
+            amount=5000000,
+            script_type=proto.OutputScriptType.PAYTOADDRESS,
+        )
+
+        out2 = proto.TxOutputType(
+            address_n=parse_path("84'/1'/0'/1/0"),
+            script_type=proto.OutputScriptType.PAYTOWITNESS,
+            multisig=multisig_out,
+            amount=12300000 + 100 - 5000000 - 10000,
+        )
+
+        with client:
+            client.set_expected_responses(
+                [
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXINPUT,
+                        details=proto.TxRequestDetailsType(request_index=0),
+                    ),
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXINPUT,
+                        details=proto.TxRequestDetailsType(request_index=1),
+                    ),
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXOUTPUT,
+                        details=proto.TxRequestDetailsType(request_index=0),
+                    ),
+                    proto.ButtonRequest(code=proto.ButtonRequestType.ConfirmOutput),
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXOUTPUT,
+                        details=proto.TxRequestDetailsType(request_index=1),
+                    ),
+                    # Ensure that the multisig output is not identified as a change output.
+                    proto.ButtonRequest(code=proto.ButtonRequestType.ConfirmOutput),
+                    proto.ButtonRequest(code=proto.ButtonRequestType.SignTx),
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXINPUT,
+                        details=proto.TxRequestDetailsType(request_index=0),
+                    ),
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXINPUT,
+                        details=proto.TxRequestDetailsType(request_index=1),
+                    ),
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXOUTPUT,
+                        details=proto.TxRequestDetailsType(request_index=0),
+                    ),
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXOUTPUT,
+                        details=proto.TxRequestDetailsType(request_index=1),
+                    ),
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXINPUT,
+                        details=proto.TxRequestDetailsType(request_index=0),
+                    ),
+                    proto.TxRequest(
+                        request_type=proto.RequestType.TXINPUT,
+                        details=proto.TxRequestDetailsType(request_index=1),
+                    ),
+                    proto.TxRequest(request_type=proto.RequestType.TXFINISHED),
+                ]
+            )
+
+            _, serialized_tx = btc.sign_tx(
+                client, "Testnet", [inp1, inp2], [out1, out2], prev_txes=TX_API
+            )
+
+        assert (
+            serialized_tx.hex()
+            == "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"
+        )