Add checks for settxfee reasonableness

Author: ajtowns

src/wallet/rpcwallet.cpp

@@ -2982,8 +2982,16 @@ static UniValue settxfee(const JSONRPCRequest& request)
     LOCK2(cs_main, pwallet->cs_wallet);
 
     CAmount nAmount = AmountFromValue(request.params[0]);
+    CFeeRate tx_fee_rate(nAmount, 1000);
+    if (tx_fee_rate == 0) {
+        // automatic selection
+    } else if (tx_fee_rate < ::minRelayTxFee) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("txfee cannot be less than min relay tx fee (%s)", ::minRelayTxFee.ToString()));
+    } else if (tx_fee_rate < pwallet->m_min_fee) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("txfee cannot be less than wallet min fee (%s)", pwallet->m_min_fee.ToString()));
+    }
 
-    pwallet->m_pay_tx_fee = CFeeRate(nAmount, 1000);
+    pwallet->m_pay_tx_fee = tx_fee_rate;
     return true;
 }