Enforce valid range of LoanSet.InterestRate

- Addresses FIND-002 from audit.
- Enforces a range of 0-100% in 1/10 bips.
- Also add a couple of unit test checks.

include/xrpl/protocol/Protocol.h

@@ -146,6 +146,14 @@ static_assert(maxCoverRate == TenthBips32(100'000u));
     Valid values are between 0 and 100% inclusive.
 */
 TenthBips32 constexpr maxOverpaymentFee = percentageToTenthBips(100);
+static_assert(maxOverpaymentFee == TenthBips32(100'000u));
+
+/** Annualized interest rate of the Loan in 1/10 bips.
+ *
+ * Valid values are between 0 and 100% inclusive.
+ */
+TenthBips32 constexpr maxInterestRate = percentageToTenthBips(100);
+static_assert(maxInterestRate == TenthBips32(100'000u));
 
 /** The maximum premium added to the interest rate for late payments on a loan
  * in 1/10 bips.
@@ -153,6 +161,7 @@ TenthBips32 constexpr maxOverpaymentFee = percentageToTenthBips(100);
  * Valid values are between 0 and 100% inclusive.
  */
 TenthBips32 constexpr maxLateInterestRate = percentageToTenthBips(100);
+static_assert(maxLateInterestRate == TenthBips32(100'000u));
 
 /** The maximum close interest rate charged for repaying a loan early in 1/10
  * bips.
@@ -160,6 +169,7 @@ TenthBips32 constexpr maxLateInterestRate = percentageToTenthBips(100);
  * Valid values are between 0 and 100% inclusive.
  */
 TenthBips32 constexpr maxCloseInterestRate = percentageToTenthBips(100);
+static_assert(maxCloseInterestRate == TenthBips32(100'000u));
 
 /** The maximum overpayment interest rate charged on loan overpayments in 1/10
  * bips.
@@ -167,6 +177,7 @@ TenthBips32 constexpr maxCloseInterestRate = percentageToTenthBips(100);
  * Valid values are between 0 and 100% inclusive.
  */
 TenthBips32 constexpr maxOverpaymentInterestRate = percentageToTenthBips(100);
+static_assert(maxOverpaymentInterestRate == TenthBips32(100'000u));
 
 /** The maximum length of a URI inside an NFT */
 std::size_t constexpr maxTokenURILength = 256;

src/test/app/Loan_test.cpp

@@ -748,6 +748,19 @@ class Loan_test : public beast::unit_test::suite
             loanSetFee,
             ter(temINVALID));
 
+        // sfInterestRate: good value, bad account
+        env(set(evan, broker.brokerID, principalRequest, startDate),
+            sig(sfCounterpartySignature, borrower),
+            interestRate(maxInterestRate),
+            loanSetFee,
+            ter(tefBAD_AUTH));
+        // sfInterestRate: too big
+        env(set(evan, broker.brokerID, principalRequest, startDate),
+            sig(sfCounterpartySignature, lender),
+            interestRate(maxInterestRate + 1),
+            loanSetFee,
+            ter(temINVALID));
+
         // sfLateInterestRate: good value, bad account
         env(set(evan, broker.brokerID, principalRequest, startDate),
             sig(sfCounterpartySignature, borrower),

src/xrpld/app/tx/detail/LoanSet.cpp

@@ -82,6 +82,8 @@ LoanSet::preflight(PreflightContext const& ctx)
     if (auto const data = tx[~sfData]; data && !data->empty() &&
         !validDataLength(tx[~sfData], maxDataPayloadLength))
         return temINVALID;
+    if (!validNumericRange(tx[~sfInterestRate], maxInterestRate))
+        return temINVALID;
     if (!validNumericRange(tx[~sfOverpaymentFee], maxOverpaymentFee))
         return temINVALID;
     if (!validNumericRange(tx[~sfLateInterestRate], maxLateInterestRate))