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Fix LibFixedMath arithmetic overflows #2255

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Oct 11, 2019
Merged

Fix LibFixedMath arithmetic overflows #2255

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a42f3d1
`@0x/contracts-staking`: Implement better overflow detection in `LibF…
dorothy-zbornak Oct 6, 2019
09c0b83
`@0x/utils`: Consolidated FixedMathRevertErrors
dorothy-zbornak Oct 10, 2019
063d6ff
`@0x/contracts-staking`: Add more overflow safeguards to `LibFixedMath`.
dorothy-zbornak Oct 10, 2019
22fc0b4
`@0x/contracts-staking`: Add another `LibFixedMath.add()` test.
dorothy-zbornak Oct 10, 2019
a22ba86
Update changelogs
dorothy-zbornak Oct 10, 2019
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9 changes: 9 additions & 0 deletions contracts/staking/CHANGELOG.json
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Original file line number Diff line number Diff line change
@@ -1,4 +1,13 @@
[
{
"version": "1.1.0-beta.1",
"changes": [
{
"note": "Add more overflow safeguards to `LibFixedMath`",
"pr": 2255
}
]
},
{
"version": "1.1.0-beta.0",
"changes": [
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30 changes: 22 additions & 8 deletions contracts/staking/contracts/src/libs/LibFixedMath.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,8 @@ library LibFixedMath {

// 1
int256 private constant FIXED_1 = int256(0x0000000000000000000000000000000080000000000000000000000000000000);
// 2**255
int256 private constant MIN_FIXED_VAL = int256(0x8000000000000000000000000000000000000000000000000000000000000000);
// 1^2 (in fixed-point)
int256 private constant FIXED_1_SQUARED = int256(0x4000000000000000000000000000000000000000000000000000000000000000);
// 1
Expand All @@ -50,6 +52,12 @@ library LibFixedMath {

/// @dev Returns the addition of two fixed point numbers, reverting on overflow.
function sub(int256 a, int256 b) internal pure returns (int256 c) {
if (b == MIN_FIXED_VAL) {
LibRichErrors.rrevert(LibFixedMathRichErrors.SignedValueError(
LibFixedMathRichErrors.ValueErrorCodes.TOO_SMALL,
b
));
}
c = _add(a, -b);
}

Expand Down Expand Up @@ -87,6 +95,12 @@ library LibFixedMath {

/// @dev Returns the absolute value of a fixed point number.
function abs(int256 f) internal pure returns (int256 c) {
if (f == MIN_FIXED_VAL) {
LibRichErrors.rrevert(LibFixedMathRichErrors.SignedValueError(
LibFixedMathRichErrors.ValueErrorCodes.TOO_SMALL,
f
));
}
if (f >= 0) {
c = f;
} else {
Expand Down Expand Up @@ -353,20 +367,20 @@ library LibFixedMath {
b
));
}
if (a == MIN_FIXED_VAL && b == -1) {
LibRichErrors.rrevert(LibFixedMathRichErrors.BinOpError(
LibFixedMathRichErrors.BinOpErrorCodes.DIVISION_OVERFLOW,
a,
b
));
}
c = a / b;
}

/// @dev Adds two numbers, reverting on overflow.
function _add(int256 a, int256 b) private pure returns (int256 c) {
c = a + b;
if (c > 0 && a < 0 && b < 0) {
LibRichErrors.rrevert(LibFixedMathRichErrors.BinOpError(
LibFixedMathRichErrors.BinOpErrorCodes.SUBTRACTION_OVERFLOW,
a,
b
));
}
if (c < 0 && a > 0 && b > 0) {
if ((a < 0 && b < 0 && c > a) || (a > 0 && b > 0 && c < a)) {
LibRichErrors.rrevert(LibFixedMathRichErrors.BinOpError(
LibFixedMathRichErrors.BinOpErrorCodes.ADDITION_OVERFLOW,
a,
Expand Down
4 changes: 2 additions & 2 deletions contracts/staking/contracts/src/libs/LibFixedMathRichErrors.sol
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Expand Up @@ -30,9 +30,9 @@ library LibFixedMathRichErrors {

enum BinOpErrorCodes {
ADDITION_OVERFLOW,
SUBTRACTION_OVERFLOW,
MULTIPLICATION_OVERFLOW,
DIVISION_BY_ZERO
DIVISION_BY_ZERO,
DIVISION_OVERFLOW
}

// bytes4(keccak256("SignedValueError(uint8,int256)"))
Expand Down
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