From 8565fdf7226d92dfe2af32bac75cafd126165fc7 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Mon, 10 Apr 2017 17:51:18 +0700
Subject: [PATCH] fix limit of undecrytable packets queue length

fixes #517
Also fixes an off-by-one error, such that the queue now holds exactly
protocol.MaxUndecrytablePackets packets when enough undecryptable
packets are received.
---
 session.go      | 12 ++++++++----
 session_test.go | 19 ++++++++++++++++---
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/session.go b/session.go
index 11c940d8..a8eaf39f 100644
--- a/session.go
+++ b/session.go
@@ -782,12 +782,16 @@ func (s *session) tryQueueingUndecryptablePacket(p *receivedPacket) {
 	if s.cryptoSetup.HandshakeComplete() {
 		return
 	}
-	utils.Infof("Queueing packet 0x%x for later decryption", p.publicHeader.PacketNumber)
-	if len(s.undecryptablePackets)+1 >= protocol.MaxUndecryptablePackets && s.receivedTooManyUndecrytablePacketsTime.IsZero() {
-		s.receivedTooManyUndecrytablePacketsTime = time.Now()
-		s.maybeResetTimer()
+	if len(s.undecryptablePackets)+1 > protocol.MaxUndecryptablePackets {
+		// if this is the first time the undecryptablePackets runs full, start the timer to send a Public Reset
+		if s.receivedTooManyUndecrytablePacketsTime.IsZero() {
+			s.receivedTooManyUndecrytablePacketsTime = time.Now()
+			s.maybeResetTimer()
+		}
+		utils.Infof("Dropping undecrytable packet 0x%x (undecryptable packet queue full)", p.publicHeader.PacketNumber)
 		return
 	}
+	utils.Infof("Queueing packet 0x%x for later decryption", p.publicHeader.PacketNumber)
 	s.undecryptablePackets = append(s.undecryptablePackets, p)
 }
 
diff --git a/session_test.go b/session_test.go
index a996618a..009d3f39 100644
--- a/session_test.go
+++ b/session_test.go
@@ -1193,7 +1193,7 @@ var _ = Describe("Session", func() {
 	Context("sending a Public Reset when receiving undecryptable packets during the handshake", func() {
 		It("doesn't immediately send a Public Reset after receiving too many undecryptable packets", func() {
 			go sess.run()
-			for i := 0; i < protocol.MaxUndecryptablePackets; i++ {
+			for i := 0; i < protocol.MaxUndecryptablePackets+1; i++ {
 				hdr := &PublicHeader{
 					PacketNumber: protocol.PacketNumber(i + 1),
 				}
@@ -1205,7 +1205,7 @@ var _ = Describe("Session", func() {
 
 		It("sets a deadline to send a Public Reset after receiving too many undecryptable packets", func() {
 			go sess.run()
-			for i := 0; i < protocol.MaxUndecryptablePackets; i++ {
+			for i := 0; i < protocol.MaxUndecryptablePackets+1; i++ {
 				hdr := &PublicHeader{
 					PacketNumber: protocol.PacketNumber(i + 1),
 				}
@@ -1214,6 +1214,19 @@ var _ = Describe("Session", func() {
 			Eventually(func() time.Time { return sess.receivedTooManyUndecrytablePacketsTime }).Should(BeTemporally("~", time.Now(), 10*time.Millisecond))
 		})
 
+		It("drops undecryptable packets when the undecrytable packet queue is full", func() {
+			go sess.run()
+			for i := 0; i < protocol.MaxUndecryptablePackets+10; i++ {
+				hdr := &PublicHeader{
+					PacketNumber: protocol.PacketNumber(i + 1),
+				}
+				sess.handlePacket(&receivedPacket{publicHeader: hdr, data: []byte("foobar")})
+			}
+			Eventually(func() []*receivedPacket { return sess.undecryptablePackets }).Should(HaveLen(protocol.MaxUndecryptablePackets))
+			// check that old packets are kept, and the new packets are dropped
+			Expect(sess.undecryptablePackets[0].publicHeader.PacketNumber).To(Equal(protocol.PacketNumber(1)))
+		})
+
 		It("sends a Public Reset after a timeout", func() {
 			sess.receivedTooManyUndecrytablePacketsTime = time.Now().Add(-protocol.PublicResetTimeout)
 			go sess.run()
@@ -1226,7 +1239,7 @@ var _ = Describe("Session", func() {
 
 		It("ignores undecryptable packets after the handshake is complete", func() {
 			*(*bool)(unsafe.Pointer(reflect.ValueOf(sess.cryptoSetup).Elem().FieldByName("receivedForwardSecurePacket").UnsafeAddr())) = true
-			for i := 0; i < protocol.MaxUndecryptablePackets; i++ {
+			for i := 0; i < protocol.MaxUndecryptablePackets+1; i++ {
 				hdr := &PublicHeader{
 					PacketNumber: protocol.PacketNumber(i + 1),
 				}