fix(math): defend NewIntFromBigInt argument mutation (#17352)

cosmos · Aug 10, 2023 · 658a88a · 658a88a
1 parent c3c82e2
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diff --git a/math/CHANGELOG.md b/math/CHANGELOG.md
@@ -43,6 +43,7 @@ Ref: https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.j
 
 ### Bug Fixes
 
+* [#17352](https://github.com/cosmos/cosmos-sdk/pull/17352) Ensure that modifying the argument to `NewIntFromBigInt` doesn't mutate the returned value.
 * [#16266](https://github.com/cosmos/cosmos-sdk/pull/16266) fix: legacy dec power mut zero exponent precision.
 
 ## [math/v1.0.1](https://github.com/cosmos/cosmos-sdk/releases/tag/math/v1.0.1) - 2023-05-15

diff --git a/math/int.go b/math/int.go
@@ -106,6 +106,7 @@ func NewIntFromUint64(n uint64) Int {
 
 // NewIntFromBigInt constructs Int from big.Int. If the provided big.Int is nil,
 // it returns an empty instance. This function panics if the bit length is > 256.
+// Note, the caller can safely mutate the argument after this function returns.
 func NewIntFromBigInt(i *big.Int) Int {
 	if i == nil {
 		return Int{}
@@ -114,7 +115,8 @@ func NewIntFromBigInt(i *big.Int) Int {
 	if i.BitLen() > MaxBitLen {
 		panic("NewIntFromBigInt() out of bound")
 	}
-	return Int{i}
+
+	return Int{new(big.Int).Set(i)}
 }
 
 // NewIntFromString constructs Int from string

diff --git a/math/int_test.go b/math/int_test.go
@@ -43,6 +43,19 @@ func (s *intTestSuite) TestFromUint64() {
 	}
 }
 
+func (s *intTestSuite) TestNewIntFromBigInt() {
+	i := math.NewIntFromBigInt(nil)
+	s.Require().True(i.IsNil())
+
+	r := big.NewInt(42)
+	i = math.NewIntFromBigInt(r)
+	s.Require().Equal(r, i.BigInt())
+
+	// modify r and ensure i doesn't change
+	r = r.SetInt64(100)
+	s.Require().NotEqual(r, i.BigInt())
+}
+
 func (s *intTestSuite) TestIntPanic() {
 	// Max Int = 2^256-1 = 1.1579209e+77
 	// Min Int = -(2^256-1) = -1.1579209e+77