From 127c977ab04d56de78c5caf16a8e6446eda340d4 Mon Sep 17 00:00:00 2001
From: Nicolas Lacasse <nlacasse@google.com>
Date: Thu, 26 Jul 2018 15:54:55 -0700
Subject: Don't copy-up extended attributes that specifically configure a lower
 overlay.

When copying-up files from a lower fs to an upper, we also copy the extended
attributes on the file. If there is a (nested) overlay inside the lower, some
of these extended attributes configure the lower overlay, and should not be
copied-up to the upper.

In particular, whiteout attributes in the lower fs overlay should not be
copied-up, since the upper fs may actually contain the file.

PiperOrigin-RevId: 206236010
Change-Id: Ia0454ac7b99d0e11383f732a529cb195ed364062
---
 pkg/sentry/fs/copy_up.go | 5 +++++
 pkg/sentry/fs/overlay.go | 7 +++++++
 2 files changed, 12 insertions(+)

(limited to 'pkg')

diff --git a/pkg/sentry/fs/copy_up.go b/pkg/sentry/fs/copy_up.go
index ea74d0efd..8c949b176 100644
--- a/pkg/sentry/fs/copy_up.go
+++ b/pkg/sentry/fs/copy_up.go
@@ -402,6 +402,11 @@ func copyAttributesLocked(ctx context.Context, upper *Inode, lower *Inode) error
 		return err
 	}
 	for name := range lowerXattr {
+		// Don't copy-up attributes that configure an overlay in the
+		// lower.
+		if isXattrOverlay(name) {
+			continue
+		}
 		value, err := lower.Getxattr(name)
 		if err != nil {
 			return err
diff --git a/pkg/sentry/fs/overlay.go b/pkg/sentry/fs/overlay.go
index a63f00e0e..7357d6401 100644
--- a/pkg/sentry/fs/overlay.go
+++ b/pkg/sentry/fs/overlay.go
@@ -16,6 +16,7 @@ package fs
 
 import (
 	"fmt"
+	"strings"
 	"sync"
 
 	"gvisor.googlesource.com/gvisor/pkg/log"
@@ -76,6 +77,12 @@ func XattrOverlayWhiteout(name string) string {
 	return XattrOverlayWhiteoutPrefix + name
 }
 
+// isXattrOverlay returns whether the given extended attribute configures the
+// overlay.
+func isXattrOverlay(name string) bool {
+	return strings.HasPrefix(name, XattrOverlayPrefix)
+}
+
 // NewOverlayRoot produces the root of an overlay.
 //
 // Preconditions:
-- 
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