From 59597d23a5ee268c66df96b930f651256661b8c5 Mon Sep 17 00:00:00 2001
From: obscuren <geffobscura@gmail.com>
Date: Sat, 4 Apr 2015 21:29:23 +0200
Subject: [PATCH] Reject integers w/ appended zero's

---
 rlp/decode.go      | 9 +++++++++
 rlp/decode_test.go | 1 +
 2 files changed, 10 insertions(+)

diff --git a/rlp/decode.go b/rlp/decode.go
index 0fde0a9473..3b5617475b 100644
--- a/rlp/decode.go
+++ b/rlp/decode.go
@@ -99,6 +99,8 @@ func (err *decodeError) Error() string {
 
 func wrapStreamError(err error, typ reflect.Type) error {
 	switch err {
+	case ErrCanonInt:
+		return &decodeError{msg: "canon int error appends zero's", typ: typ}
 	case ErrExpectedList:
 		return &decodeError{msg: "expected input list", typ: typ}
 	case ErrExpectedString:
@@ -184,6 +186,12 @@ func decodeBigInt(s *Stream, val reflect.Value) error {
 		i = new(big.Int)
 		val.Set(reflect.ValueOf(i))
 	}
+
+	// Reject big integers which are zero appended
+	if len(b) > 0 && b[0] == 0 {
+		return wrapStreamError(ErrCanonInt, val.Type())
+	}
+
 	i.SetBytes(b)
 	return nil
 }
@@ -460,6 +468,7 @@ var (
 	// Other errors
 	ErrExpectedString = errors.New("rlp: expected String or Byte")
 	ErrExpectedList   = errors.New("rlp: expected List")
+	ErrCanonInt       = errors.New("rlp: expected Int")
 	ErrElemTooLarge   = errors.New("rlp: element is larger than containing list")
 
 	// internal errors
diff --git a/rlp/decode_test.go b/rlp/decode_test.go
index a18ff1d080..73a31c67f5 100644
--- a/rlp/decode_test.go
+++ b/rlp/decode_test.go
@@ -312,6 +312,7 @@ var decodeTests = []decodeTest{
 	// big ints
 	{input: "01", ptr: new(*big.Int), value: big.NewInt(1)},
 	{input: "89FFFFFFFFFFFFFFFFFF", ptr: new(*big.Int), value: veryBigInt},
+	{input: "820001", ptr: new(big.Int), error: "rlp: canon int error appends zero's for *big.Int"},
 	{input: "10", ptr: new(big.Int), value: *big.NewInt(16)}, // non-pointer also works
 	{input: "C0", ptr: new(*big.Int), error: "rlp: expected input string or byte for *big.Int"},