net: correctly ban before the handshake is complete

7a8c251901 made a change to avoid getting into SendMessages() until the
version handshake (VERSION + VERACK) is complete. That was done to avoid
leaking out messages to nodes who could connect, but never bothered sending
us their version/verack.

Unfortunately, the ban tally and possible disconnect are done as part of
SendMessages(). So after 7a8c251901, if a peer managed to do something
bannable before completing the handshake (say send 100 non-version messages
before their version), they wouldn't actually end up getting
disconnected/banned. That's fixed here by checking the banscore as part of
ProcessMessages() in addition to SendMessages().

src/net_processing.cpp

@@ -2596,6 +2596,36 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
     return true;
 }
 
+static bool SendRejectsAndCheckIfBanned(CNode* pnode, CConnman& connman)
+{
+    AssertLockHeld(cs_main);
+    CNodeState &state = *State(pnode->GetId());
+
+    BOOST_FOREACH(const CBlockReject& reject, state.rejects) {
+        connman.PushMessage(pnode, CNetMsgMaker(INIT_PROTO_VERSION).Make(NetMsgType::REJECT, (std::string)NetMsgType::BLOCK, reject.chRejectCode, reject.strRejectReason, reject.hashBlock));
+    }
+    state.rejects.clear();
+
+    if (state.fShouldBan) {
+        state.fShouldBan = false;
+        if (pnode->fWhitelisted)
+            LogPrintf("Warning: not punishing whitelisted peer %s!\n", pnode->addr.ToString());
+        else if (pnode->fAddnode)
+            LogPrintf("Warning: not punishing addnoded peer %s!\n", pnode->addr.ToString());
+        else {
+            pnode->fDisconnect = true;
+            if (pnode->addr.IsLocal())
+                LogPrintf("Warning: not banning local peer %s!\n", pnode->addr.ToString());
+            else
+            {
+                connman.Ban(pnode->addr, BanReasonNodeMisbehaving);
+            }
+        }
+        return true;
+    }
+    return false;
+}
+
 bool ProcessMessages(CNode* pfrom, CConnman& connman, const std::atomic<bool>& interruptMsgProc)
 {
     const CChainParams& chainparams = Params();
@@ -2706,8 +2736,12 @@ bool ProcessMessages(CNode* pfrom, CConnman& connman, const std::atomic<bool>& i
             PrintExceptionContinue(NULL, "ProcessMessages()");
         }
 
-        if (!fRet)
+        if (!fRet) {
             LogPrintf("%s(%s, %u bytes) FAILED peer=%d\n", __func__, SanitizeString(strCommand), nMessageSize, pfrom->id);
+        }
+
+        LOCK(cs_main);
+        SendRejectsAndCheckIfBanned(pfrom, connman);
 
     return fMoreWork;
 }
@@ -2773,29 +2807,9 @@ bool SendMessages(CNode* pto, CConnman& connman, const std::atomic<bool>& interr
         if (!lockMain)
             return true;
 
-        CNodeState &state = *State(pto->GetId());
-
-        BOOST_FOREACH(const CBlockReject& reject, state.rejects)
-            connman.PushMessage(pto, msgMaker.Make(NetMsgType::REJECT, (std::string)NetMsgType::BLOCK, reject.chRejectCode, reject.strRejectReason, reject.hashBlock));
-        state.rejects.clear();
-
-        if (state.fShouldBan) {
-            state.fShouldBan = false;
-            if (pto->fWhitelisted)
-                LogPrintf("Warning: not punishing whitelisted peer %s!\n", pto->addr.ToString());
-            else if (pto->fAddnode)
-                LogPrintf("Warning: not punishing addnoded peer %s!\n", pto->addr.ToString());
-            else {
-                pto->fDisconnect = true;
-                if (pto->addr.IsLocal())
-                    LogPrintf("Warning: not banning local peer %s!\n", pto->addr.ToString());
-                else
-                {
-                    connman.Ban(pto->addr, BanReasonNodeMisbehaving);
-                }
+        if (SendRejectsAndCheckIfBanned(pto, connman))
             return true;
-            }
-        }
+        CNodeState &state = *State(pto->GetId());
 
         // Address refresh broadcast
         int64_t nNow = GetTimeMicros();