[nice to have] multisig preventing signing with wrong key (#286)

## Describe your changes and provide context
Doesn't seem to be absolutely necessary since it would just fail when
broadcasting, more of an UI improvement. We can wait until 3.0.4 is out
and then merging

Copying from: cosmos/cosmos-sdk#12548

## Testing performed to validate your change
unit tests

x/auth/client/cli/tx_sign.go

@@ -4,12 +4,14 @@ import (
 	"fmt"
 	"os"
 
+	"github.com/cosmos/cosmos-sdk/crypto/keyring"
 	"github.com/spf13/cobra"
 
 	"github.com/cosmos/cosmos-sdk/client"
 	"github.com/cosmos/cosmos-sdk/client/flags"
 	"github.com/cosmos/cosmos-sdk/client/tx"
-	sdk "github.com/cosmos/cosmos-sdk/types"
+	kmultisig "github.com/cosmos/cosmos-sdk/crypto/keys/multisig"
+	"github.com/cosmos/cosmos-sdk/types/errors"
 	authclient "github.com/cosmos/cosmos-sdk/x/auth/client"
 )
 
@@ -215,7 +217,6 @@ func makeSignCmd() func(cmd *cobra.Command, args []string) error {
 			return err
 		}
 
-		txFactory := tx.NewFactoryCLI(clientCtx, cmd.Flags())
 		txCfg := clientCtx.TxConfig
 		txBuilder, err := txCfg.WrapTxBuilder(newTx)
 		if err != nil {
@@ -235,14 +236,33 @@ func makeSignCmd() func(cmd *cobra.Command, args []string) error {
 
 		overwrite, _ := f.GetBool(flagOverwrite)
 		if multisig != "" {
-			multisigAddr, err := sdk.AccAddressFromBech32(multisig)
+			// Bech32 decode error, maybe it's a name, we try to fetch from keyring
+			multisigAddr, multisigName, _, err := client.GetFromFields(txF.Keybase(), multisig, clientCtx.GenerateOnly)
 			if err != nil {
-				// Bech32 decode error, maybe it's a name, we try to fetch from keyring
-				multisigAddr, _, _, err = client.GetFromFields(txFactory.Keybase(), multisig, clientCtx.GenerateOnly)
-				if err != nil {
-					return fmt.Errorf("error getting account from keybase: %w", err)
+				return fmt.Errorf("error getting account from keybase: %w", err)
+			}
+			multisigkey, err := getMultisigRecord(clientCtx, multisigName)
+			if err != nil {
+				return err
+			}
+			multisigPubKey := multisigkey.GetPubKey()
+			multisigLegacyPub := multisigPubKey.(*kmultisig.LegacyAminoPubKey)
+
+			fromRecord, err := clientCtx.Keyring.Key(fromName)
+			if err != nil {
+				return fmt.Errorf("error getting account from keybase: %w", err)
+			}
+			fromPubKey := fromRecord.GetPubKey()
+
+			var found bool
+			for _, pubkey := range multisigLegacyPub.GetPubKeys() {
+				if pubkey.Equals(fromPubKey) {
+					found = true
 				}
 			}
+			if !found {
+				return fmt.Errorf("signing key is not a part of multisig key")
+			}
 			err = authclient.SignTxWithSignerAddress(
 				txF, clientCtx, multisigAddr, fromName, txBuilder, clientCtx.Offline, overwrite)
 			if err != nil {
@@ -316,3 +336,13 @@ func marshalSignatureJSON(txConfig client.TxConfig, txBldr client.TxBuilder, sig
 
 	return txConfig.TxJSONEncoder()(parsedTx)
 }
+
+func getMultisigRecord(clientCtx client.Context, name string) (keyring.Info, error) {
+	kb := clientCtx.Keyring
+	multisigRecord, err := kb.Key(name)
+	if err != nil {
+		return nil, errors.Wrap(err, "error getting keybase multisig account")
+	}
+
+	return multisigRecord, nil
+}

x/auth/client/testutil/suite.go

@@ -60,6 +60,10 @@ func (s *IntegrationTestSuite) SetupSuite() {
 	account2, _, err := kb.NewMnemonic("newAccount2", keyring.English, sdk.FullFundraiserPath, keyring.DefaultBIP39Passphrase, hd.Secp256k1)
 	s.Require().NoError(err)
 
+	// Create a dummy account for testing purpose
+	_, _, err = kb.NewMnemonic("dummyAccount", keyring.English, sdk.FullFundraiserPath, keyring.DefaultBIP39Passphrase, hd.Secp256k1)
+	s.Require().NoError(err)
+
 	multi := kmultisig.NewLegacyAminoPubKey(2, []cryptotypes.PubKey{account1.GetPubKey(), account2.GetPubKey()})
 	_, err = kb.SaveMultisig("multi", multi)
 	s.Require().NoError(err)
@@ -737,6 +741,10 @@ func (s *IntegrationTestSuite) TestCLIMultisignSortSignatures() {
 	multisigInfo, err := val1.ClientCtx.Keyring.Key("multi")
 	s.Require().NoError(err)
 
+	// Generate dummy account which is not a part of multisig.
+	dummyAcc, err := val1.ClientCtx.Keyring.Key("dummyAccount")
+	s.Require().NoError(err)
+
 	resp, err := bankcli.QueryBalancesExec(val1.ClientCtx, multisigInfo.GetAddress())
 	s.Require().NoError(err)
 
@@ -789,12 +797,19 @@ func (s *IntegrationTestSuite) TestCLIMultisignSortSignatures() {
 
 	sign1File := testutil.WriteToNewTempFile(s.T(), account1Signature.String())
 
-	// Sign with account1
+	// Sign with account2
 	account2Signature, err := TxSignExec(val1.ClientCtx, account2.GetAddress(), multiGeneratedTxFile.Name(), "--multisig", multisigInfo.GetAddress().String())
 	s.Require().NoError(err)
 
 	sign2File := testutil.WriteToNewTempFile(s.T(), account2Signature.String())
 
+	// Sign with dummy account
+	dummyAddr := dummyAcc.GetAddress()
+	s.Require().NoError(err)
+	_, err = TxSignExec(val1.ClientCtx, dummyAddr, multiGeneratedTxFile.Name(), "--multisig", multisigInfo.GetAddress().String())
+	s.Require().Error(err)
+	s.Require().Contains(err.Error(), "signing key is not a part of multisig key")
+
 	multiSigWith2Signatures, err := TxMultiSignExec(val1.ClientCtx, multisigInfo.GetName(), multiGeneratedTxFile.Name(), sign1File.Name(), sign2File.Name())
 	s.Require().NoError(err)
 
@@ -849,7 +864,7 @@ func (s *IntegrationTestSuite) TestSignWithMultisig() {
 	// as the main point of this test is to test the `--multisig` flag with an address
 	// that is not in the keyring.
 	_, err = TxSignExec(val1.ClientCtx, addr1, multiGeneratedTx2File.Name(), "--multisig", multisigAddr.String())
-	s.Require().Contains(err.Error(), "tx intended signer does not match the given signer")
+	s.Require().Contains(err.Error(), "error getting account from keybase")
 }
 
 func (s *IntegrationTestSuite) TestCLIMultisign() {