From 424f53fa0c60fd62cb77186ffb9643dae5429a5c Mon Sep 17 00:00:00 2001 From: Dave Cheney Date: Wed, 4 Jan 2012 10:36:21 -0500 Subject: [PATCH] exp/ssh: fix two flow control bugs in chanWriter This CL fixes two issues sending data to the remote peer. The first bug occurs when the size of the buffer passed to Write is larger than the current window, in this case, w.rwin can become negative. The second issue is more problematic than the first as the amount of data passed to writePacket was not limited to w.rwin. In this case the remote peer could silently drop the additional data, or drop the connection. Credit to Jacek Masiulaniec for the bug report. R=agl, jacek.masiulaniec CC=golang-dev https://golang.org/cl/5511043 --- src/pkg/exp/ssh/client.go | 34 ++++++++++++++++++++++------------ 1 file changed, 22 insertions(+), 12 deletions(-) diff --git a/src/pkg/exp/ssh/client.go b/src/pkg/exp/ssh/client.go index 7c862078b7..8df81457bf 100644 --- a/src/pkg/exp/ssh/client.go +++ b/src/pkg/exp/ssh/client.go @@ -420,27 +420,37 @@ type chanWriter struct { } // Write writes data to the remote process's standard input. -func (w *chanWriter) Write(data []byte) (n int, err error) { - for { - if w.rwin == 0 { +func (w *chanWriter) Write(data []byte) (written int, err error) { + for len(data) > 0 { + for w.rwin < 1 { win, ok := <-w.win if !ok { return 0, io.EOF } w.rwin += win - continue } + n := min(len(data), w.rwin) peersId := w.clientChan.peersId - n = len(data) - packet := make([]byte, 0, 9+n) - packet = append(packet, msgChannelData, - byte(peersId>>24), byte(peersId>>16), byte(peersId>>8), byte(peersId), - byte(n>>24), byte(n>>16), byte(n>>8), byte(n)) - err = w.clientChan.writePacket(append(packet, data...)) + packet := []byte{ + msgChannelData, + byte(peersId >> 24), byte(peersId >> 16), byte(peersId >> 8), byte(peersId), + byte(n >> 24), byte(n >> 16), byte(n >> 8), byte(n), + } + if err = w.clientChan.writePacket(append(packet, data[:n]...)); err != nil { + break + } + data = data[n:] w.rwin -= n - return + written += n } - panic("unreachable") + return +} + +func min(a, b int) int { + if a < b { + return a + } + return b } func (w *chanWriter) Close() error { -- 2.50.0