From 160316d53c8a757695542b1071e251be41ae913a Mon Sep 17 00:00:00 2001
From: mmmray <142015632+mmmray@users.noreply.github.com>
Date: Sat, 17 Aug 2024 13:01:58 +0200
Subject: [PATCH] SplitHTTP: Do not produce too large upload (#3691)

---
 transport/internet/splithttp/dialer.go        | 46 +++++++++++++--
 .../internet/splithttp/splithttp_test.go      | 56 ++++++++++++++++++-
 transport/pipe/impl.go                        |  8 +++
 transport/pipe/writer.go                      |  4 ++
 4 files changed, 108 insertions(+), 6 deletions(-)

diff --git a/transport/internet/splithttp/dialer.go b/transport/internet/splithttp/dialer.go
index 0d487b58..a95ab34b 100644
--- a/transport/internet/splithttp/dialer.go
+++ b/transport/internet/splithttp/dialer.go
@@ -227,7 +227,11 @@ func Dial(ctx context.Context, dest net.Destination, streamSettings *internet.Me
 
 	httpClient := getHTTPClient(ctx, dest, streamSettings)
 
-	uploadPipeReader, uploadPipeWriter := pipe.New(pipe.WithSizeLimit(scMaxEachPostBytes.roll()))
+	maxUploadSize := scMaxEachPostBytes.roll()
+	// WithSizeLimit(0) will still allow single bytes to pass, and a lot of
+	// code relies on this behavior. Subtract 1 so that together with
+	// uploadWriter wrapper, exact size limits can be enforced
+	uploadPipeReader, uploadPipeWriter := pipe.New(pipe.WithSizeLimit(maxUploadSize - 1))
 
 	go func() {
 		requestsLimiter := semaphore.New(int(scMaxConcurrentPosts.roll()))
@@ -318,12 +322,13 @@ func Dial(ctx context.Context, dest net.Destination, streamSettings *internet.Me
 		},
 	}
 
-	// necessary in order to send larger chunks in upload
-	bufferedUploadPipeWriter := buf.NewBufferedWriter(uploadPipeWriter)
-	bufferedUploadPipeWriter.SetBuffered(false)
+	writer := uploadWriter{
+		uploadPipeWriter,
+		maxUploadSize,
+	}
 
 	conn := splitConn{
-		writer:     bufferedUploadPipeWriter,
+		writer:     writer,
 		reader:     lazyDownload,
 		remoteAddr: remoteAddr,
 		localAddr:  localAddr,
@@ -331,3 +336,34 @@ func Dial(ctx context.Context, dest net.Destination, streamSettings *internet.Me
 
 	return stat.Connection(&conn), nil
 }
+
+// A wrapper around pipe that ensures the size limit is exactly honored.
+//
+// The MultiBuffer pipe accepts any single WriteMultiBuffer call even if that
+// single MultiBuffer exceeds the size limit, and then starts blocking on the
+// next WriteMultiBuffer call. This means that ReadMultiBuffer can return more
+// bytes than the size limit. We work around this by splitting a potentially
+// too large write up into multiple.
+type uploadWriter struct {
+	*pipe.Writer
+	maxLen int32
+}
+
+func (w uploadWriter) Write(b []byte) (int, error) {
+	capacity := int(w.maxLen - w.Len())
+	if capacity > 0 && capacity < len(b) {
+		b = b[:capacity]
+	}
+
+	buffer := buf.New()
+	n, err := buffer.Write(b)
+	if err != nil {
+		return 0, err
+	}
+
+	err = w.WriteMultiBuffer([]*buf.Buffer{buffer})
+	if err != nil {
+		return 0, err
+	}
+	return n, nil
+}
diff --git a/transport/internet/splithttp/splithttp_test.go b/transport/internet/splithttp/splithttp_test.go
index acb4addc..30f92c7f 100644
--- a/transport/internet/splithttp/splithttp_test.go
+++ b/transport/internet/splithttp/splithttp_test.go
@@ -388,7 +388,7 @@ func Test_queryString(t *testing.T) {
 	ctx := context.Background()
 	streamSettings := &internet.MemoryStreamConfig{
 		ProtocolName:     "splithttp",
-		ProtocolSettings: &Config{Path: "sh"},
+		ProtocolSettings: &Config{Path: "sh?ed=2048"},
 	}
 	conn, err := Dial(ctx, net.TCPDestination(net.DomainAddress("localhost"), listenPort), streamSettings)
 
@@ -407,3 +407,57 @@ func Test_queryString(t *testing.T) {
 	common.Must(conn.Close())
 	common.Must(listen.Close())
 }
+
+func Test_maxUpload(t *testing.T) {
+	listenPort := tcp.PickPort()
+	streamSettings := &internet.MemoryStreamConfig{
+		ProtocolName: "splithttp",
+		ProtocolSettings: &Config{
+			Path: "/sh",
+			ScMaxEachPostBytes: &RandRangeConfig{
+				From: 100,
+				To:   100,
+			},
+		},
+	}
+
+	var uploadSize int
+	listen, err := ListenSH(context.Background(), net.LocalHostIP, listenPort, streamSettings, func(conn stat.Connection) {
+		go func(c stat.Connection) {
+			defer c.Close()
+			var b [1024]byte
+			c.SetReadDeadline(time.Now().Add(2 * time.Second))
+			n, err := c.Read(b[:])
+			if err != nil {
+				return
+			}
+
+			uploadSize = n
+
+			common.Must2(c.Write([]byte("Response")))
+		}(conn)
+	})
+	common.Must(err)
+	ctx := context.Background()
+
+	conn, err := Dial(ctx, net.TCPDestination(net.DomainAddress("localhost"), listenPort), streamSettings)
+
+	// send a slightly too large upload
+	var upload [101]byte
+	_, err = conn.Write(upload[:])
+	common.Must(err)
+
+	var b [1024]byte
+	n, _ := io.ReadFull(conn, b[:])
+	fmt.Println("string is", n)
+	if string(b[:n]) != "Response" {
+		t.Error("response: ", string(b[:n]))
+	}
+	common.Must(conn.Close())
+
+	if uploadSize > 100 || uploadSize == 0 {
+		t.Error("incorrect upload size: ", uploadSize)
+	}
+
+	common.Must(listen.Close())
+}
diff --git a/transport/pipe/impl.go b/transport/pipe/impl.go
index dbdb050e..8bf58a34 100644
--- a/transport/pipe/impl.go
+++ b/transport/pipe/impl.go
@@ -46,6 +46,14 @@ var (
 	errSlowDown   = errors.New("slow down")
 )
 
+func (p *pipe) Len() int32 {
+    data := p.data
+    if data == nil {
+        return 0
+    }
+    return data.Len()
+}
+
 func (p *pipe) getState(forRead bool) error {
 	switch p.state {
 	case open:
diff --git a/transport/pipe/writer.go b/transport/pipe/writer.go
index 8230ec76..0a192ca0 100644
--- a/transport/pipe/writer.go
+++ b/transport/pipe/writer.go
@@ -19,6 +19,10 @@ func (w *Writer) Close() error {
 	return w.pipe.Close()
 }
 
+func (w *Writer) Len() int32 {
+    return w.pipe.Len()
+}
+
 // Interrupt implements common.Interruptible.
 func (w *Writer) Interrupt() {
 	w.pipe.Interrupt()