fix: reject overflowing ABI offsets and contain decode panics in the evm log parser (F-2026-18804)

Author: Aman035

universalClient/chains/evm/event_parser.go

@@ -29,7 +29,27 @@ const (
 
 // ParseEvent parses a log into a store.Event based on the event type.
 // eventType should be one of: sendFunds, executeUniversalTx, revertUniversalTx.
-func ParseEvent(log *types.Log, eventType string, chainID string, logger zerolog.Logger) *store.Event {
+//
+// A panic in the decoders is contained here rather than allowed to unwind. Log
+// data is supplied by an RPC and the listener runs on a background goroutine, so
+// an unrecovered panic would take down every chain and the TSS node with it. A
+// log we cannot decode is skipped like any other undecodable one.
+func ParseEvent(log *types.Log, eventType string, chainID string, logger zerolog.Logger) (event *store.Event) {
+	defer func() {
+		if r := recover(); r != nil {
+			event = nil
+			logger.Error().
+				Interface("panic", r).
+				Str("event_type", eventType).
+				Str("tx_hash", log.TxHash.Hex()).
+				Uint("log_index", log.Index).
+				Msg("panic while decoding log; skipping it")
+		}
+	}()
+	return parseEvent(log, eventType, chainID, logger)
+}
+
+func parseEvent(log *types.Log, eventType string, chainID string, logger zerolog.Logger) *store.Event {
 	if len(log.Topics) == 0 {
 		return nil
 	}
@@ -175,17 +195,24 @@ func parseUniversalTxEvent(event *store.Event, log *types.Log, chainID string, l
 }
 
 // readDynamicBytes decodes ABI-encoded dynamic bytes at the given absolute offset in data.
+//
+// Both absOff and the length word are attacker-controlled: they come from the
+// log data an RPC returns. Bounds are therefore checked by subtracting from the
+// buffer length rather than adding to the offset — absOff+32 and dataStart+byteLen
+// each wrap on a near-2^64 word and would pass an additive guard, then panic on
+// the slice.
 func readDynamicBytes(data []byte, absOff uint64) (string, bool) {
-	if absOff+32 > uint64(len(data)) {
+	n := uint64(len(data))
+	if absOff > n || n-absOff < 32 {
 		return "", false
 	}
 	byteLen := new(big.Int).SetBytes(data[absOff : absOff+32]).Uint64()
-	dataStart := absOff + 32
-	dataEnd := dataStart + byteLen
-	if dataEnd > uint64(len(data)) {
+
+	dataStart := absOff + 32 // safe: absOff+32 <= n was just established
+	if n-dataStart < byteLen {
 		return "", false
 	}
-	return "0x" + hex.EncodeToString(data[dataStart:dataEnd]), true
+	return "0x" + hex.EncodeToString(data[dataStart : dataStart+byteLen]), true
 }
 
 // readWord returns the i-th 32-byte word from data, or nil if out of bounds.

universalClient/chains/evm/event_parser_test.go

@@ -3,6 +3,7 @@ package evm
 import (
 	"encoding/hex"
 	"encoding/json"
+	"math"
 	"math/big"
 	"testing"
 
@@ -656,3 +657,102 @@ func TestFinalizeEvent(t *testing.T) {
 		assert.Equal(t, "1000", decoded.Amount)
 	})
 }
+
+// abiWord returns a 32-byte big-endian word holding v, for building hostile log data.
+func abiWord(v *big.Int) []byte {
+	w := make([]byte, 32)
+	v.FillBytes(w)
+	return w
+}
+
+// Both the offset and the length word come from the RPC, so both can be chosen
+// to overflow uint64. Addition-based bounds wrap and pass, then the slice panics
+// — and the listener has no caller between here and the goroutine root, so that
+// panic would end the process.
+func TestReadDynamicBytes_OverflowIsRejectedNotPanicked(t *testing.T) {
+	maxU64 := new(big.Int).SetUint64(math.MaxUint64)
+
+	t.Run("offset near 2^64 does not wrap past the bounds check", func(t *testing.T) {
+		data := make([]byte, 128)
+		for _, off := range []uint64{
+			math.MaxUint64,      // absOff + 32 wraps to 31
+			math.MaxUint64 - 16, // wraps to 15
+			math.MaxUint64 - 31, // wraps to 0
+			math.MaxUint64 - 32, // wraps to exactly 0 after the +32
+		} {
+			_, ok := readDynamicBytes(data, off)
+			assert.False(t, ok, "offset %d must be rejected", off)
+		}
+	})
+
+	t.Run("length near 2^64 does not wrap the end below the start", func(t *testing.T) {
+		// Word at offset 0 is the length; make it enormous so dataStart+byteLen wraps.
+		data := make([]byte, 128)
+		copy(data[0:32], abiWord(maxU64))
+
+		_, ok := readDynamicBytes(data, 0)
+		assert.False(t, ok, "a length that wraps the end must be rejected")
+	})
+
+	t.Run("length just past the buffer is rejected without wrapping", func(t *testing.T) {
+		data := make([]byte, 128)
+		copy(data[0:32], abiWord(big.NewInt(97))) // 32 header + 97 > 128
+		_, ok := readDynamicBytes(data, 0)
+		assert.False(t, ok)
+	})
+
+	t.Run("well formed input still decodes", func(t *testing.T) {
+		data := make([]byte, 128)
+		copy(data[0:32], abiWord(big.NewInt(4)))
+		copy(data[32:36], []byte{0xDE, 0xAD, 0xBE, 0xEF})
+
+		got, ok := readDynamicBytes(data, 0)
+		require.True(t, ok)
+		assert.Equal(t, "0xdeadbeef", got)
+	})
+
+	t.Run("zero length decodes to empty", func(t *testing.T) {
+		data := make([]byte, 64)
+		got, ok := readDynamicBytes(data, 0)
+		require.True(t, ok)
+		assert.Equal(t, "0x", got)
+	})
+
+	t.Run("exactly filling the buffer decodes", func(t *testing.T) {
+		data := make([]byte, 64)
+		copy(data[0:32], abiWord(big.NewInt(32)))
+		copy(data[32:64], abiWord(big.NewInt(1)))
+
+		_, ok := readDynamicBytes(data, 32+32-32) // offset 32 is past the end for a 64-byte buffer
+		assert.False(t, ok)
+
+		got, ok := readDynamicBytes(data, 0)
+		require.True(t, ok)
+		assert.Len(t, got, 2+64)
+	})
+}
+
+// End to end: a log carrying an overflowing payload offset must be skipped, not
+// crash the listener goroutine.
+func TestParseEvent_HostileLogDoesNotPanic(t *testing.T) {
+	// 5 words of data so the length guard passes, with word 2 (the payload
+	// offset) set to a value that overflows when 32 is added to it.
+	data := make([]byte, 32*5)
+	copy(data[2*32:3*32], abiWord(new(big.Int).SetUint64(math.MaxUint64)))
+
+	log := &types.Log{
+		Topics: []ethcommon.Hash{
+			ethcommon.HexToHash("0x01"),
+			ethcommon.HexToHash("0x02"),
+			ethcommon.HexToHash("0x03"),
+		},
+		Data:    data,
+		TxHash:  ethcommon.HexToHash("0xabc"),
+		Index:   7,
+		Address: ethcommon.HexToAddress("0xdead"),
+	}
+
+	require.NotPanics(t, func() {
+		ParseEvent(log, EventTypeSendFunds, "eip155:1", zerolog.Nop())
+	})
+}