From 96fd50be10885c9b3033404df698177fdb63d036 Mon Sep 17 00:00:00 2001
From: Martin Holst Swende <martin@swende.se>
Date: Mon, 1 Oct 2018 14:17:37 +0200
Subject: [PATCH] accounts/abi: fix panic in MethodById lookup. Fixes #17797
 (#17798)

---
 accounts/abi/abi.go      |  3 +++
 accounts/abi/abi_test.go | 11 ++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/accounts/abi/abi.go b/accounts/abi/abi.go
index 254b1f7fb..535e5d78b 100644
--- a/accounts/abi/abi.go
+++ b/accounts/abi/abi.go
@@ -137,6 +137,9 @@ func (abi *ABI) UnmarshalJSON(data []byte) error {
 // MethodById looks up a method by the 4-byte id
 // returns nil if none found
 func (abi *ABI) MethodById(sigdata []byte) (*Method, error) {
+	if len(sigdata) < 4 {
+		return nil, fmt.Errorf("data too short (% bytes) for abi method lookup", len(sigdata))
+	}
 	for _, method := range abi.Methods {
 		if bytes.Equal(method.Id(), sigdata[:4]) {
 			return &method, nil
diff --git a/accounts/abi/abi_test.go b/accounts/abi/abi_test.go
index 8018df775..59ba79cb6 100644
--- a/accounts/abi/abi_test.go
+++ b/accounts/abi/abi_test.go
@@ -711,5 +711,14 @@ func TestABI_MethodById(t *testing.T) {
 			t.Errorf("Method %v (id %v) not 'findable' by id in ABI", name, common.ToHex(m.Id()))
 		}
 	}
-
+	// Also test empty
+	if _, err := abi.MethodById([]byte{0x00}); err == nil {
+		t.Errorf("Expected error, too short to decode data")
+	}
+	if _, err := abi.MethodById([]byte{}); err == nil {
+		t.Errorf("Expected error, too short to decode data")
+	}
+	if _, err := abi.MethodById(nil); err == nil {
+		t.Errorf("Expected error, nil is short to decode data")
+	}
 }