pulsar: fix mlen uint64 overflow → chain-halt (CRITICAL launch blocker)

verify parsed mlen from attacker's low-8-bytes, then guarded with
len(body) < mlen+sigSize — which OVERFLOWS uint64 when mlen is near MaxUint64,
slipping past the guard so body[:mlen] panics. A panic in geth's precompile
dispatch has no recover() → every validator halts on the tx. Fixed with a
non-overflowing subtraction guard (mlen > len(body) || len(body)-mlen < sigSize).
Regression test TestVerify_MlenOverflowRejected proves reject-not-panic.
Red-team finding #5.

pulsar/contract.go

@@ -193,7 +193,12 @@ func (p *pulsarVerifyPrecompile) Run(
 		mlen = (mlen << 8) | uint64(body[i])
 	}
 	body = body[32:]
-	if uint64(len(body)) < mlen+uint64(sigSize) {
+	// Bounds check WITHOUT overflow: mlen is attacker-controlled (low 8 bytes
+	// of a uint256), so mlen+sigSize can wrap uint64 and slip past a naive
+	// guard, making body[:mlen] panic — and a panic in the geth precompile
+	// dispatch (no recover) halts every validator on the tx. Compare with
+	// subtraction on the trusted len(body) instead.
+	if mlen > uint64(len(body)) || uint64(len(body))-mlen < uint64(sigSize) {
 		return nil, suppliedGas, ErrInvalidInputLength
 	}
 	msg := body[:mlen]

pulsar/overflow_test.go

@@ -0,0 +1,38 @@
+// Copyright (C) 2025-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package pulsar
+
+import (
+	"encoding/binary"
+	"testing"
+
+	"github.com/luxfi/geth/common"
+)
+
+// TestVerify_MlenOverflowRejected proves the consensus-halt fix: an attacker
+// who sets the message-length field near MaxUint64 must get a clean
+// ErrInvalidInputLength, NOT a slice-out-of-range panic. A panic in geth's
+// precompile dispatch has no recover() — it would halt every validator on the
+// tx. Before the fix, mlen+sigSize wrapped uint64, the guard passed, and
+// body[:mlen] panicked.
+func TestVerify_MlenOverflowRejected(t *testing.T) {
+	p := PulsarVerifyPrecompile
+
+	input := []byte{ModePulsar44}
+	input = append(input, make([]byte, Pulsar44PublicKeySize)...)
+	lenField := make([]byte, 32)
+	binary.BigEndian.PutUint64(lenField[24:], ^uint64(0)-8)
+	input = append(input, lenField...)
+	input = append(input, make([]byte, 64)...)
+
+	defer func() {
+		if r := recover(); r != nil {
+			t.Fatalf("CONSENSUS-HALT: overflow mlen panicked instead of rejecting: %v", r)
+		}
+	}()
+	_, _, err := p.Run(nil, common.Address{}, common.Address{}, input, 100_000_000, true)
+	if err == nil {
+		t.Fatal("expected ErrInvalidInputLength for overflow mlen, got nil")
+	}
+}