Hard Audit: don't convert directly from sdk.Int to uint64 (#842)

* refactor away from sdk.Int's .Uint64() method * refactor cdp module interest calc
Kava-Labs · Feb 20, 2021 · fe43c2b · fe43c2b
1 parent 5cd9404
commit fe43c2b
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Showing 3 changed files with 22 additions and 4 deletions.
diff --git a/x/cdp/keeper/interest.go b/x/cdp/keeper/interest.go
@@ -93,9 +93,11 @@ func CalculateInterestFactor(perSecondInterestRate sdk.Dec, secondsElapsed sdk.I
 	scalingFactorInt := sdk.NewInt(int64(scalingFactor))
 
 	// Convert per-second interest rate to a uint scaled by 1e18
-	interestMantissa := sdk.NewUint(perSecondInterestRate.MulInt(scalingFactorInt).RoundInt().Uint64())
+	interestMantissa := sdk.NewUintFromBigInt(perSecondInterestRate.MulInt(scalingFactorInt).RoundInt().BigInt())
+
 	// Convert seconds elapsed to uint (*not scaled*)
-	secondsElapsedUint := sdk.NewUint(secondsElapsed.Uint64())
+	secondsElapsedUint := sdk.NewUintFromBigInt(secondsElapsed.BigInt())
+
 	// Calculate the interest factor as a uint scaled by 1e18
 	interestFactorMantissa := sdk.RelativePow(interestMantissa, secondsElapsedUint, scalingFactorUint)
 

diff --git a/x/hard/keeper/interest.go b/x/hard/keeper/interest.go
@@ -193,9 +193,9 @@ func CalculateBorrowInterestFactor(perSecondInterestRate sdk.Dec, secondsElapsed
 	scalingFactorInt := sdk.NewInt(int64(scalingFactor))
 
 	// Convert per-second interest rate to a uint scaled by 1e18
-	interestMantissa := sdk.NewUint(perSecondInterestRate.MulInt(scalingFactorInt).RoundInt().Uint64())
+	interestMantissa := sdk.NewUintFromBigInt(perSecondInterestRate.MulInt(scalingFactorInt).RoundInt().BigInt())
 	// Convert seconds elapsed to uint (*not scaled*)
-	secondsElapsedUint := sdk.NewUint(secondsElapsed.Uint64())
+	secondsElapsedUint := sdk.NewUintFromBigInt(secondsElapsed.BigInt())
 	// Calculate the interest factor as a uint scaled by 1e18
 	interestFactorMantissa := sdk.RelativePow(interestMantissa, secondsElapsedUint, scalingFactorUint)
 

diff --git a/x/hard/keeper/interest_test.go b/x/hard/keeper/interest_test.go
@@ -306,6 +306,22 @@ func (suite *InterestTestSuite) TestCalculateBorrowInterestFactor() {
 				expectedValue:         sdk.MustNewDecFromStr("94702138679846565921082258202543002089.215969366091911769"),
 			},
 		},
+		{
+			"supports calculated values greater than 1.84x10^19",
+			args{
+				perSecondInterestRate: sdk.MustNewDecFromStr("18.5"), // Old uint64 conversion would panic at ~18.45 (1845%/second interest rate)
+				timeElapsed:           sdk.NewInt(30),                // Assume a 30 second period, longer than any expected individual block
+				expectedValue:         sdk.MustNewDecFromStr("103550416986452240450480615551792302106.072205164469778538"),
+			},
+		},
+		{
+			"largest per second interest rate before sdk.Uint overflows 256 bytes",
+			args{
+				perSecondInterestRate: sdk.MustNewDecFromStr("23.3"), // 23.4 overflows bit length 256 by 1 byte
+				timeElapsed:           sdk.NewInt(30),                // Assume a 30 second period, longer than any expected individual block
+				expectedValue:         sdk.MustNewDecFromStr("104876366068119517411103023062013348034546.437155815200037999"),
+			},
+		},
 	}
 
 	for _, tc := range testCases {