From c99e092a3bb986b03fd85d426e166ef2c73a8c51 Mon Sep 17 00:00:00 2001
From: Tamir Duberstein <tamird@google.com>
Date: Thu, 28 Jan 2021 17:38:47 -0800
Subject: Propagate reader error in ReadFrom

This was removed in 6c0e1d9cfe6adbfbb32e7020d6426608ac63ad37 but turns
out to be crucial to prevent flaky behaviour in sendfile.

PiperOrigin-RevId: 354434144
---
 pkg/sentry/socket/netstack/netstack.go | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

(limited to 'pkg/sentry/socket/netstack')

diff --git a/pkg/sentry/socket/netstack/netstack.go b/pkg/sentry/socket/netstack/netstack.go
index 3115a227d..30a31ef4c 100644
--- a/pkg/sentry/socket/netstack/netstack.go
+++ b/pkg/sentry/socket/netstack/netstack.go
@@ -459,17 +459,24 @@ func (s *SocketOperations) Write(ctx context.Context, _ *fs.File, src usermem.IO
 var _ tcpip.Payloader = (*limitedPayloader)(nil)
 
 type limitedPayloader struct {
-	io.LimitedReader
+	inner io.LimitedReader
+	err   error
 }
 
-func (l limitedPayloader) Len() int {
-	return int(l.N)
+func (l *limitedPayloader) Read(p []byte) (int, error) {
+	n, err := l.inner.Read(p)
+	l.err = err
+	return n, err
+}
+
+func (l *limitedPayloader) Len() int {
+	return int(l.inner.N)
 }
 
 // ReadFrom implements fs.FileOperations.ReadFrom.
 func (s *SocketOperations) ReadFrom(ctx context.Context, _ *fs.File, r io.Reader, count int64) (int64, error) {
 	f := limitedPayloader{
-		LimitedReader: io.LimitedReader{
+		inner: io.LimitedReader{
 			R: r,
 			N: count,
 		},
@@ -480,7 +487,7 @@ func (s *SocketOperations) ReadFrom(ctx context.Context, _ *fs.File, r io.Reader
 		Atomic: true,
 	})
 	if err == tcpip.ErrBadBuffer {
-		err = nil
+		return n, f.err
 	}
 	return n, syserr.TranslateNetstackError(err).ToError()
 }
-- 
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