From 56f165bdc1ad3940fee2e345aa2706f502866c67 Mon Sep 17 00:00:00 2001
From: kazcw <keziahw@gmail.com>
Date: Wed, 16 Jul 2014 14:31:41 -0700
Subject: [PATCH 1/2] prevent peer flooding request queue for an inv

mapAlreadyAskedFor does not keep track of which peer has a request queued for a
particular tx. As a result, a peer can blind a node to a tx indefinitely by
sending many invs for the same tx, and then never replying to getdatas for it.
Each inv received will be placed 2 minutes farther back in mapAlreadyAskedFor,
so a short message containing 10 invs would render that tx unavailable for 20
minutes.

This is fixed by disallowing a peer from having more than one entry for a
particular inv in mapAlreadyAskedFor at a time.
---
 src/main.cpp | 1 +
 src/net.cpp  | 4 ++++
 src/net.h    | 1 +
 3 files changed, 6 insertions(+)

diff --git a/src/main.cpp b/src/main.cpp
index 082456af2..88686df6d 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -5452,6 +5452,7 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                     vGetData.clear();
                 }
             }
+            pto->setAskFor.erase(inv.hash);
             pto->mapAskFor.erase(pto->mapAskFor.begin());
         }
         if (!vGetData.empty())
diff --git a/src/net.cpp b/src/net.cpp
index 04e48ac62..710e61678 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2180,6 +2180,10 @@ void CNode::AskFor(const CInv& inv)
 {
     if (mapAskFor.size() > MAPASKFOR_MAX_SZ)
         return;
+    // a peer may not occupy multiple positions in an inv's request queue
+    if (!setAskFor.insert(inv.hash).second)
+        return;
+
     // We're using mapAskFor as a priority queue,
     // the key is the earliest time the request can be sent
     int64_t nRequestTime;
diff --git a/src/net.h b/src/net.h
index 66f733e01..bc6ab291a 100644
--- a/src/net.h
+++ b/src/net.h
@@ -310,6 +310,7 @@ public:
     mruset<CInv> setInventoryKnown;
     std::vector<CInv> vInventoryToSend;
     CCriticalSection cs_inventory;
+    std::set<uint256> setAskFor;
     std::multimap<int64_t, CInv> mapAskFor;
 
     // Ping time measurement:

From e2190f8017ece64ecd31321e6e44f466d2224cf6 Mon Sep 17 00:00:00 2001
From: Gregory Maxwell <greg@xiph.org>
Date: Mon, 23 Nov 2015 01:54:23 +0000
Subject: [PATCH 2/2] Limit setAskFor and retire requested entries only when a
 getdata returns.

The setAskFor duplicate elimination was too eager and removed entries
 when we still had no getdata response, allowing the peer to keep
 INVing and not responding.
---
 src/main.cpp | 5 ++++-
 src/net.cpp  | 4 ++--
 src/net.h    | 2 ++
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 88686df6d..94fa6aeca 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4657,6 +4657,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         bool fMissingInputs = false;
         CValidationState state;
 
+        pfrom->setAskFor.erase(inv.hash);
         mapAlreadyAskedFor.erase(inv);
 
         // Check for recently rejected (and do other quick existence checks)
@@ -5451,8 +5452,10 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                     pto->PushMessage("getdata", vGetData);
                     vGetData.clear();
                 }
+            } else {
+                //If we're not going to ask, don't expect a response.
+                pto->setAskFor.erase(inv.hash);
             }
-            pto->setAskFor.erase(inv.hash);
             pto->mapAskFor.erase(pto->mapAskFor.begin());
         }
         if (!vGetData.empty())
diff --git a/src/net.cpp b/src/net.cpp
index 710e61678..636e3d5e7 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2178,9 +2178,9 @@ CNode::~CNode()
 
 void CNode::AskFor(const CInv& inv)
 {
-    if (mapAskFor.size() > MAPASKFOR_MAX_SZ)
+    if (mapAskFor.size() > MAPASKFOR_MAX_SZ || setAskFor.size() > SETASKFOR_MAX_SZ)
         return;
-    // a peer may not occupy multiple positions in an inv's request queue
+    // a peer may not have multiple non-responded queue positions for a single inv item
     if (!setAskFor.insert(inv.hash).second)
         return;
 
diff --git a/src/net.h b/src/net.h
index bc6ab291a..44f14fd43 100644
--- a/src/net.h
+++ b/src/net.h
@@ -59,6 +59,8 @@ static const bool DEFAULT_UPNP = false;
 #endif
 /** The maximum number of entries in mapAskFor */
 static const size_t MAPASKFOR_MAX_SZ = MAX_INV_SZ;
+/** The maximum number of entries in setAskFor (larger due to getdata latency)*/
+static const size_t SETASKFOR_MAX_SZ = 2 * MAX_INV_SZ;
 
 unsigned int ReceiveFloodSize();
 unsigned int SendBufferSize();