Audit fixes (#613)

* TokenForceCloseBorrows: Respect reduce-only flag
* ForceCancelOrders: Readability of early-out condition

programs/mango-v4/src/instructions/perp_liq_force_cancel_orders.rs

@@ -23,10 +23,10 @@ pub fn perp_liq_force_cancel_orders(
     // Early return if if liquidation is not allowed or if market is not in force close
     //
     let liquidatable = account.check_liquidatable(&health_cache)?;
-    if account.fixed.is_operational()
-        && liquidatable != CheckLiquidatable::Liquidatable
-        && !perp_market.is_force_close()
-    {
+    let can_force_cancel = !account.fixed.is_operational()
+        || liquidatable == CheckLiquidatable::Liquidatable
+        || perp_market.is_force_close();
+    if !can_force_cancel {
         return Ok(());
     }
 

programs/mango-v4/src/instructions/serum3_liq_force_cancel_orders.rs

@@ -60,14 +60,12 @@ pub fn serum3_liq_force_cancel_orders(
         let health_cache =
             new_health_cache(&account.borrow(), &retriever).context("create health cache")?;
 
-        {
-            let liquidatable = account.check_liquidatable(&health_cache)?;
-            if account.fixed.is_operational()
-                && liquidatable != CheckLiquidatable::Liquidatable
-                && !serum_market.is_force_close()
-            {
-                return Ok(());
-            }
+        let liquidatable = account.check_liquidatable(&health_cache)?;
+        let can_force_cancel = !account.fixed.is_operational()
+            || liquidatable == CheckLiquidatable::Liquidatable
+            || serum_market.is_force_close();
+        if !can_force_cancel {
+            return Ok(());
         }
 
         health_cache

programs/mango-v4/src/instructions/token_force_close_borrows_with_token.rs

@@ -56,6 +56,12 @@ pub fn token_force_close_borrows_with_token(
         // account constraint #2
         require!(liab_bank.is_force_close(), MangoError::TokenInForceClose);
 
+        // We might create asset borrows, so forbid asset tokens that don't allow them.
+        require!(
+            !asset_bank.are_borrows_reduce_only(),
+            MangoError::TokenInReduceOnlyMode
+        );
+
         // account constraint #3
         // only allow combination of asset and liab token,
         // where liqee's health would be guaranteed to not decrease