From ee24dffae2f31f38c3b1a48314f4bf25a92820c7 Mon Sep 17 00:00:00 2001
From: Oleksii Matiiasevych <lastperson@gmail.com>
Date: Wed, 26 Oct 2016 12:41:56 +0300
Subject: [PATCH] Prevent re-entrancy, fix balance check logic

---
 swarm/services/chequebook/contract/chequebook.sol | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/swarm/services/chequebook/contract/chequebook.sol b/swarm/services/chequebook/contract/chequebook.sol
index cb19d0b27b..6443bd18a1 100644
--- a/swarm/services/chequebook/contract/chequebook.sol
+++ b/swarm/services/chequebook/contract/chequebook.sol
@@ -27,10 +27,12 @@ contract chequebook is mortal {
         if(owner != ecrecover(hash, sig_v, sig_r, sig_s)) return;
         // Attempt sending the difference between the cumulative amount on the cheque
         // and the cumulative amount on the last cashed cheque to beneficiary.
-        if (amount - sent[beneficiary] >= this.balance) {
-            if (beneficiary.send(amount - sent[beneficiary])) {
-                // Upon success, update the cumulative amount.
-                sent[beneficiary] = amount;
+        if (amount - sent[beneficiary] <= this.balance) {
+            // Update the cumulative amount upfront to prevent re-entrancy.
+            sent[beneficiary] = amount;
+            if (!beneficiary.send(amount - sent[beneficiary])) {
+                // Upon failure, rollback.
+                throw;
             }
         } else {
             // Upon failure, punish owner for writing a bounced cheque.