Merge branch '0.5.x' into 0.6.0.x

Conflicts:
	bitcoin-qt.pro
	doc/README
	doc/README_windows.txt
	share/setup.nsi
	src/serialize.h

1 files changed, 41 insertions, 6 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 7d3432751a..129e09929a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2168,6 +2168,28 @@ bool CAlert::ProcessAlert()
     if (!IsInEffect())
         return false;
 
+    // alert.nID=max is reserved for if the alert key is
+    // compromised. It must have a pre-defined message,
+    // must never expire, must apply to all versions,
+    // and must cancel all previous
+    // alerts or it will be ignored (so an attacker can't
+    // send an "everything is OK, don't panic" version that
+    // cannot be overridden):
+    int maxInt = std::numeric_limits<int>::max();
+    if (nID == maxInt)
+    {
+        if (!(
+                nExpiration == maxInt &&
+                nCancel == (maxInt-1) &&
+                nMinVer == 0 &&
+                nMaxVer == maxInt &&
+                setSubVer.empty() &&
+                nPriority == maxInt &&
+                strStatusBar == "URGENT: Alert key compromised, upgrade required"
+                ))
+            return false;
+    }
+
     CRITICAL_BLOCK(cs_mapAlerts)
     {
         // Cancel previous alerts
@@ -2780,13 +2802,26 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
         CAlert alert;
         vRecv >> alert;
 
-        if (alert.ProcessAlert())
+        uint256 alertHash = alert.GetHash();
+        if (pfrom->setKnown.count(alertHash) == 0)
         {
-            // Relay
-            pfrom->setKnown.insert(alert.GetHash());
-            CRITICAL_BLOCK(cs_vNodes)
-                BOOST_FOREACH(CNode* pnode, vNodes)
-                    alert.RelayTo(pnode);
+            if (alert.ProcessAlert())
+            {
+                // Relay
+                pfrom->setKnown.insert(alertHash);
+                CRITICAL_BLOCK(cs_vNodes)
+                    BOOST_FOREACH(CNode* pnode, vNodes)
+                        alert.RelayTo(pnode);
+            }
+            else {
+                // Small DoS penalty so peers that send us lots of
+                // duplicate/expired/invalid-signature/whatever alerts
+                // eventually get banned.
+                // This isn't a Misbehaving(100) (immediate ban) because the
+                // peer might be an older or different implementation with
+                // a different signature key, etc.
+                pfrom->Misbehaving(10);
+            }
         }
     }