From 5556edbcad3df786071133dec7583d566cf30001 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Fri, 20 Oct 2017 23:11:57 +0700
Subject: [PATCH] fix parsing of long reason phrases in CONNECTION_CLOSE frames

---
 internal/wire/connection_close_frame.go      | 8 ++++++--
 internal/wire/connection_close_frame_test.go | 5 +++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/internal/wire/connection_close_frame.go b/internal/wire/connection_close_frame.go
index 96c25c1ea..432c6a866 100644
--- a/internal/wire/connection_close_frame.go
+++ b/internal/wire/connection_close_frame.go
@@ -38,12 +38,16 @@ func ParseConnectionCloseFrame(r *bytes.Reader, version protocol.VersionNumber)
 		return nil, err
 	}
 
-	if reasonPhraseLen > uint16(protocol.MaxPacketSize) {
-		return nil, qerr.Error(qerr.InvalidConnectionCloseData, "reason phrase too long")
+	// shortcut to prevent the unneccessary allocation of dataLen bytes
+	// if the dataLen is larger than the remaining length of the packet
+	// reading the whole reason phrase would result in EOF when attempting to READ
+	if int(reasonPhraseLen) > r.Len() {
+		return nil, io.EOF
 	}
 
 	reasonPhrase := make([]byte, reasonPhraseLen)
 	if _, err := io.ReadFull(r, reasonPhrase); err != nil {
+		// this should never happen, since we already checked the reasonPhraseLen earlier
 		return nil, err
 	}
 	frame.ReasonPhrase = string(reasonPhrase)
diff --git a/internal/wire/connection_close_frame_test.go b/internal/wire/connection_close_frame_test.go
index 351fa843f..012ca02df 100644
--- a/internal/wire/connection_close_frame_test.go
+++ b/internal/wire/connection_close_frame_test.go
@@ -2,6 +2,7 @@ package wire
 
 import (
 	"bytes"
+	"io"
 	"strings"
 
 	"github.com/lucas-clemente/quic-go/internal/protocol"
@@ -32,7 +33,7 @@ var _ = Describe("ConnectionCloseFrame", func() {
 					0x0, 0xff, // reason phrase length
 				})
 				_, err := ParseConnectionCloseFrame(b, versionLittleEndian)
-				Expect(err).To(MatchError(qerr.Error(qerr.InvalidConnectionCloseData, "reason phrase too long")))
+				Expect(err).To(MatchError(io.EOF))
 			})
 
 			It("errors on EOFs", func() {
@@ -70,7 +71,7 @@ var _ = Describe("ConnectionCloseFrame", func() {
 					0xff, 0x0, // reason phrase length
 				})
 				_, err := ParseConnectionCloseFrame(b, versionBigEndian)
-				Expect(err).To(MatchError(qerr.Error(qerr.InvalidConnectionCloseData, "reason phrase too long")))
+				Expect(err).To(MatchError(io.EOF))
 			})
 
 			It("errors on EOFs", func() {