chore: guard localtxmonitor server against int overflows (#900)

Signed-off-by: Chris Gianelloni <[email protected]>

Author: wolf31o2

protocol/localtxmonitor/messages.go

@@ -1,4 +1,4 @@
-// Copyright 2023 Blink Labs Software
+// Copyright 2025 Blink Labs Software
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -16,6 +16,7 @@ package localtxmonitor
 
 import (
 	"fmt"
+	"math"
 
 	"github.com/blinklabs-io/gouroboros/cbor"
 	"github.com/blinklabs-io/gouroboros/protocol"
@@ -170,13 +171,21 @@ func (m *MsgReplyNextTx) UnmarshalCBOR(data []byte) error {
 	if tmp == nil {
 		return nil
 	}
+	messageType64 := tmp[0].(uint64)
+	if messageType64 > math.MaxUint8 {
+		return fmt.Errorf("message type integer overflow")
+	}
 	// We know what the value will be, but it doesn't hurt to use the actual value from the message
-	m.MessageType = uint8(tmp[0].(uint64))
+	m.MessageType = uint8(messageType64)
 	// The ReplyNextTx message has a variable number of arguments
 	if len(tmp) > 1 {
 		txWrapper := tmp[1].([]interface{})
+		eraId64 := txWrapper[0].(uint64)
+		if eraId64 > math.MaxUint8 {
+			return fmt.Errorf("era id integer overflow")
+		}
 		m.Transaction = MsgReplyNextTxTransaction{
-			EraId: uint8(txWrapper[0].(uint64)),
+			EraId: uint8(eraId64),
 			Tx:    txWrapper[1].(cbor.WrappedCbor).Bytes(),
 		}
 	}

protocol/localtxmonitor/server.go

@@ -1,4 +1,4 @@
-// Copyright 2024 Blink Labs Software
+// Copyright 2025 Blink Labs Software
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@ package localtxmonitor
 import (
 	"encoding/hex"
 	"fmt"
+	"math"
 
 	"github.com/blinklabs-io/gouroboros/ledger"
 	"github.com/blinklabs-io/gouroboros/protocol"
@@ -193,6 +194,9 @@ func (s *Server) handleNextTx() error {
 		return nil
 	}
 	mempoolTx := s.mempoolTxs[s.mempoolNextTxIdx]
+	if mempoolTx.EraId > math.MaxUint8 {
+		return fmt.Errorf("integer overflow in era id")
+	}
 	newMsg := NewMsgReplyNextTx(uint8(mempoolTx.EraId), mempoolTx.Tx)
 	if err := s.SendMessage(newMsg); err != nil {
 		return err
@@ -213,10 +217,18 @@ func (s *Server) handleGetSizes() error {
 	for _, tx := range s.mempoolTxs {
 		totalTxSize += len(tx.Tx)
 	}
+	numTxs := len(s.mempoolTxs)
+	// check for over/underflows
+	if totalTxSize < 0 || totalTxSize > math.MaxUint32 {
+		return fmt.Errorf("integrer overflow in total tx size")
+	}
+	if numTxs < 0 || numTxs > math.MaxUint32 {
+		return fmt.Errorf("integrer overflow in tx count")
+	}
 	newMsg := NewMsgReplyGetSizes(
 		s.mempoolCapacity,
-		uint32(totalTxSize),
-		uint32(len(s.mempoolTxs)),
+		uint32(totalTxSize), // #nosec G115
+		uint32(numTxs),
 	)
 	if err := s.SendMessage(newMsg); err != nil {
 		return err