[BP: release/v4 <- #71] [pfm][fix] patch arbitrary account passthrough

.gitignore

@@ -14,3 +14,6 @@
 
 # Dependency directories (remove the comment below to include it)
 # vendor/
+target/
+
+go.work.sum

middleware/packet-forward-middleware/README.md

@@ -61,8 +61,10 @@ Utilizing the packet `memo` field, instructions can be encoded as JSON for multi
 ### Minimal Example - Chain forward A->B->C
 
 - The packet-forward-middleware integrated on Chain B.
+- The packet data `receiver` for the `MsgTransfer` on Chain A is set to `"pfm"` or some other invalid bech32 string.*
 - The packet `memo` is included in `MsgTransfer` by user on Chain A.
 
+memo:
 ```
 {
   "forward": {
@@ -76,6 +78,8 @@ Utilizing the packet `memo` field, instructions can be encoded as JSON for multi
 ### Full Example - Chain forward A->B->C->D with retry on timeout
 
 - The packet-forward-middleware integrated on Chain B and Chain C.
+- The packet data `receiver` for the `MsgTransfer` on Chain A is set to `"pfm"` or some other invalid bech32 string.*
+- The forward metadata `receiver` for the hop from Chain B to Chain C is set to `"pfm"` or some other invalid bech32 string.*
 - The packet `memo` is included in `MsgTransfer` by user on Chain A.
 - A packet timeout of 10 minutes and 2 retries is set for both forwards. 
 
@@ -87,7 +91,7 @@ In the case of a timeout after 10 minutes for either forward, the packet would b
 ```
 {
   "forward": {
-    "receiver": "chain-c-bech32-address",
+    "receiver": "pfm", // purposely using invalid bech32 here*
     "port": "transfer",
     "channel": "channel-123",
     "timeout": "10m",
@@ -109,7 +113,7 @@ In the case of a timeout after 10 minutes for either forward, the packet would b
 ```
 {
   "forward": {
-    "receiver": "chain-c-bech32-address",
+    "receiver": "pfm", // purposely using invalid bech32 here*
     "port": "transfer",
     "channel": "channel-123",
     "timeout": "10m",
@@ -119,6 +123,14 @@ In the case of a timeout after 10 minutes for either forward, the packet would b
 }
 ```
 
+## Intermediate Receivers*
+
+PFM does not need the packet data `receiver` address to be valid, as it will create a hash of the sender and channel to derive a receiver address on the intermediate chains. This is done for security purposes to ensure that users cannot move funds through arbitrary accounts on intermediate chains.
+
+To prevent accidentally sending funds to a chain which does not have PFM, it is recommended to use an invalid bech32 string (such as `"pfm"`) for the `receiver` on intermediate chains.  By using an invalid bech32 string, a transfer that is accidentally sent to a chain that does not have PFM would fail to be received, and properly refunded to the user on the source chain, rather than having funds get stuck on the intermediate chain.
+
+The examples above show the intended usage of the `receiver` field for one or multiple intermediate PFM chains.
+
 ## References
 
 - https://www.mintscan.io/cosmos/proposals/56

middleware/packet-forward-middleware/router/ibc_middleware.go

@@ -11,6 +11,7 @@ import (
 	"github.com/cosmos/ibc-apps/middleware/packet-forward-middleware/v4/router/types"
 
 	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/types/address"
 	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
 	capabilitytypes "github.com/cosmos/cosmos-sdk/x/capability/types"
 
@@ -132,6 +133,28 @@ func getBoolFromAny(value any) bool {
 	return boolVal
 }
 
+// getReceiver returns the receiver address for a given channel and original sender.
+// it overrides the receiver address to be a hash of the channel/origSender so that
+// the receiver address is deterministic and can be used to identify the sender on the
+// initial chain.
+func getReceiver(channel string, originalSender string) (string, error) {
+	senderStr := fmt.Sprintf("%s/%s", channel, originalSender)
+	senderHash32 := address.Hash(types.ModuleName, []byte(senderStr))
+	sender := sdk.AccAddress(senderHash32[:20])
+	bech32Prefix := sdk.GetConfig().GetBech32AccountAddrPrefix()
+	return sdk.Bech32ifyAddressBytes(bech32Prefix, sender)
+}
+
+// newErrorAcknowledgement returns an error that identifies PFM and provides the error.
+// It's okay if these errors are non-deterministic, because they will not be committed to state, only emitted as events.
+func newErrorAcknowledgement(err error) channeltypes.Acknowledgement {
+	return channeltypes.Acknowledgement{
+		Response: &channeltypes.Acknowledgement_Error{
+			Error: fmt.Sprintf("packet-forward-middleware error: %s", err.Error()),
+		},
+	}
+}
+
 // OnRecvPacket checks the memo field on this packet and if the metadata inside's root key indicates this packet
 // should be handled by the swap middleware it attempts to perform a swap. If the swap is successful
 // the underlying application's OnRecvPacket callback is invoked, an ack error is returned otherwise.
@@ -140,12 +163,15 @@ func (im IBCMiddleware) OnRecvPacket(
 	packet channeltypes.Packet,
 	relayer sdk.AccAddress,
 ) ibcexported.Acknowledgement {
+	logger := im.keeper.Logger(ctx)
+
 	var data transfertypes.FungibleTokenPacketData
 	if err := transfertypes.ModuleCdc.UnmarshalJSON(packet.GetData(), &data); err != nil {
-		return channeltypes.NewErrorAcknowledgement(err)
+		logger.Error("packetForwardMiddleware OnRecvPacketfailed to unmarshal packet data as FungibleTokenPacketData", "error", err)
+		return newErrorAcknowledgement(fmt.Errorf("failed to unmarshal packet data as FungibleTokenPacketData: %w", err))
 	}
 
-	im.keeper.Logger(ctx).Debug("packetForwardMiddleware OnRecvPacket",
+	logger.Debug("packetForwardMiddleware OnRecvPacket",
 		"sequence", packet.Sequence,
 		"src-channel", packet.SourceChannel, "src-port", packet.SourcePort,
 		"dst-channel", packet.DestinationChannel, "dst-port", packet.DestinationPort,
@@ -156,13 +182,14 @@ func (im IBCMiddleware) OnRecvPacket(
 	err := json.Unmarshal([]byte(data.Memo), &d)
 	if err != nil || d["forward"] == nil {
 		// not a packet that should be forwarded
-		im.keeper.Logger(ctx).Debug("packetForwardMiddleware OnRecvPacket forward metadata does not exist")
+		logger.Debug("packetForwardMiddleware OnRecvPacket forward metadata does not exist")
 		return im.app.OnRecvPacket(ctx, packet, relayer)
 	}
 	m := &types.PacketMetadata{}
 	err = json.Unmarshal([]byte(data.Memo), m)
 	if err != nil {
-		return channeltypes.NewErrorAcknowledgement(fmt.Errorf("packetForwardMiddleware error parsing forward metadata, %s", err))
+		logger.Error("packetForwardMiddleware OnRecvPacket error parsing forward metadata", "error", err)
+		return newErrorAcknowledgement(fmt.Errorf("error parsing forward metadata: %w", err))
 	}
 
 	metadata := m.Forward
@@ -173,16 +200,24 @@ func (im IBCMiddleware) OnRecvPacket(
 	disableDenomComposition := getBoolFromAny(goCtx.Value(types.DisableDenomCompositionKey{}))
 
 	if err := metadata.Validate(); err != nil {
-		return channeltypes.NewErrorAcknowledgement(err)
+		logger.Error("packetForwardMiddleware OnRecvPacket forward metadata is invalid", "error", err)
+		return newErrorAcknowledgement(err)
+	}
+
+	// override the receiver so that senders cannot move funds through arbitrary addresses.
+	overrideReceiver, err := getReceiver(packet.DestinationChannel, data.Sender)
+	if err != nil {
+		logger.Error("packetForwardMiddleware OnRecvPacket failed to construct override receiver", "error", err)
+		return newErrorAcknowledgement(fmt.Errorf("failed to construct override receiver: %w", err))
 	}
 
 	// if this packet has been handled by another middleware in the stack there may be no need to call into the
 	// underlying app, otherwise the transfer module's OnRecvPacket callback could be invoked more than once
 	// which would mint/burn vouchers more than once
 	if !processed {
-		ack := im.app.OnRecvPacket(ctx, packet, relayer)
-		if ack == nil || !ack.Success() {
-			return ack
+		if err := im.receiveFunds(ctx, packet, data, overrideReceiver, relayer); err != nil {
+			logger.Error("packetForwardMiddleware OnRecvPacket error receiving packet", "error", err)
+			return newErrorAcknowledgement(fmt.Errorf("error receiving packet: %w", err))
 		}
 	}
 
@@ -199,7 +234,8 @@ func (im IBCMiddleware) OnRecvPacket(
 
 	amountInt, ok := sdk.NewIntFromString(data.Amount)
 	if !ok {
-		return channeltypes.NewErrorAcknowledgement(fmt.Errorf("error parsing amount for forward: %s", data.Amount))
+		logger.Error("packetForwardMiddleware OnRecvPacket error parsing amount for forward", "amount", data.Amount)
+		return newErrorAcknowledgement(fmt.Errorf("error parsing amount for forward: %s", data.Amount))
 	}
 
 	token := sdk.NewCoin(denomOnThisChain, amountInt)
@@ -217,16 +253,58 @@ func (im IBCMiddleware) OnRecvPacket(
 		retries = im.retriesOnTimeout
 	}
 
-	err = im.keeper.ForwardTransferPacket(ctx, nil, packet, data.Sender, data.Receiver, metadata, token, retries, timeout, []metrics.Label{}, nonrefundable)
+	err = im.keeper.ForwardTransferPacket(ctx, nil, packet, data.Sender, overrideReceiver, metadata, token, retries, timeout, []metrics.Label{}, nonrefundable)
 	if err != nil {
-		return channeltypes.NewErrorAcknowledgement(err)
+		logger.Error("packetForwardMiddleware OnRecvPacket error forwarding packet", "error", err)
+		return newErrorAcknowledgement(err)
 	}
 
 	// returning nil ack will prevent WriteAcknowledgement from occurring for forwarded packet.
 	// This is intentional so that the acknowledgement will be written later based on the ack/timeout of the forwarded packet.
 	return nil
 }
 
+// receiveFunds receives funds from the packet into the override receiver
+// address and returns an error if the funds cannot be received.
+func (im IBCMiddleware) receiveFunds(
+	ctx sdk.Context,
+	packet channeltypes.Packet,
+	data transfertypes.FungibleTokenPacketData,
+	overrideReceiver string,
+	relayer sdk.AccAddress,
+) error {
+	overrideData := transfertypes.FungibleTokenPacketData{
+		Denom:    data.Denom,
+		Amount:   data.Amount,
+		Sender:   data.Sender,
+		Receiver: overrideReceiver, // override receiver
+		// Memo explicitly zeroed
+	}
+	overrideDataBz := transfertypes.ModuleCdc.MustMarshalJSON(&overrideData)
+	overridePacket := channeltypes.Packet{
+		Sequence:           packet.Sequence,
+		SourcePort:         packet.SourcePort,
+		SourceChannel:      packet.SourceChannel,
+		DestinationPort:    packet.DestinationPort,
+		DestinationChannel: packet.DestinationChannel,
+		Data:               overrideDataBz, // override data
+		TimeoutHeight:      packet.TimeoutHeight,
+		TimeoutTimestamp:   packet.TimeoutTimestamp,
+	}
+
+	ack := im.app.OnRecvPacket(ctx, overridePacket, relayer)
+
+	if ack == nil {
+		return fmt.Errorf("ack is nil")
+	}
+
+	if !ack.Success() {
+		return fmt.Errorf("ack error: %s", string(ack.Acknowledgement()))
+	}
+
+	return nil
+}
+
 // OnAcknowledgementPacket implements the IBCModule interface.
 func (im IBCMiddleware) OnAcknowledgementPacket(
 	ctx sdk.Context,
@@ -292,7 +370,7 @@ func (im IBCMiddleware) OnTimeoutPacket(ctx sdk.Context, packet channeltypes.Pac
 			im.keeper.RemoveInFlightPacket(ctx, packet)
 			// this is a forwarded packet, so override handling to avoid refund from being processed on this chain.
 			// WriteAcknowledgement with proxied ack to return success/fail to previous chain.
-			return im.keeper.WriteAcknowledgementForForwardedPacket(ctx, packet, data, inFlightPacket, channeltypes.NewErrorAcknowledgement(err))
+			return im.keeper.WriteAcknowledgementForForwardedPacket(ctx, packet, data, inFlightPacket, newErrorAcknowledgement(err))
 		}
 		// timeout should be retried. In order to do that, we need to handle this timeout to refund on this chain first.
 		if err := im.app.OnTimeoutPacket(ctx, packet, relayer); err != nil {