Remove symlink support from kubectl cp

Author: soltysh

hack/.staticcheck_failures

@@ -26,7 +26,6 @@ pkg/credentialprovider
 pkg/credentialprovider/aws
 pkg/credentialprovider/azure
 pkg/kubeapiserver/admission
-pkg/kubectl/cmd/cp
 pkg/kubectl/cmd/get
 pkg/kubelet/apis/podresources
 pkg/kubelet/cm/devicemanager

pkg/kubectl/cmd/cp/cp.go

@@ -45,6 +45,15 @@ var (
 		# !!!Important Note!!!
 		# Requires that the 'tar' binary is present in your container
 		# image.  If 'tar' is not present, 'kubectl cp' will fail.
+		#
+		# For advanced use cases, such as symlinks, wildcard expansion or
+		# file mode preservation consider using 'kubectl exec'.
+
+		# Copy /tmp/foo local file to /tmp/bar in a remote pod in namespace <some-namespace>
+		tar cf - /tmp/foo | kubectl exec -i -n <some-namespace> <some-pod> -- tar xf - -C /tmp/bar
+
+		# Copy /tmp/foo from a remote pod to /tmp/bar locally
+		kubectl exec -n <some-namespace> <some-pod> -- tar cf - /tmp/foo | tar xf - -C /tmp/bar
 
 		# Copy /tmp/foo_dir local directory to /tmp/bar_dir in a remote pod in the default namespace
 		kubectl cp /tmp/foo_dir <some-pod>:/tmp/bar_dir
@@ -71,8 +80,9 @@ type CopyOptions struct {
 	Namespace  string
 	NoPreserve bool
 
-	ClientConfig *restclient.Config
-	Clientset    kubernetes.Interface
+	ClientConfig      *restclient.Config
+	Clientset         kubernetes.Interface
+	ExecParentCmdName string
 
 	genericclioptions.IOStreams
 }
@@ -143,6 +153,10 @@ func extractFileSpec(arg string) (fileSpec, error) {
 
 // Complete completes all the required options
 func (o *CopyOptions) Complete(f cmdutil.Factory, cmd *cobra.Command) error {
+	if cmd.Parent() != nil {
+		o.ExecParentCmdName = cmd.Parent().CommandPath()
+	}
+
 	var err error
 	o.Namespace, _, err = f.ToRawKubeConfigLoader().Namespace()
 	if err != nil {
@@ -307,7 +321,7 @@ func (o *CopyOptions) copyFromPod(src, dest fileSpec) error {
 	// remove extraneous path shortcuts - these could occur if a path contained extra "../"
 	// and attempted to navigate beyond "/" in a remote filesystem
 	prefix = stripPathShortcuts(prefix)
-	return o.untarAll(reader, dest.File, prefix)
+	return o.untarAll(src, reader, dest.File, prefix)
 }
 
 // stripPathShortcuts removes any leading or trailing "../" from a given path
@@ -412,7 +426,8 @@ func recursiveTar(srcBase, srcFile, destBase, destFile string, tw *tar.Writer) e
 	return nil
 }
 
-func (o *CopyOptions) untarAll(reader io.Reader, destDir, prefix string) error {
+func (o *CopyOptions) untarAll(src fileSpec, reader io.Reader, destDir, prefix string) error {
+	symlinkWarningPrinted := false
 	// TODO: use compression here?
 	tarReader := tar.NewReader(reader)
 	for {
@@ -453,48 +468,25 @@ func (o *CopyOptions) untarAll(reader io.Reader, destDir, prefix string) error {
 			continue
 		}
 
-		// We need to ensure that the destination file is always within boundries
-		// of the destination directory. This prevents any kind of path traversal
-		// from within tar archive.
-		evaledPath, err := filepath.EvalSymlinks(baseName)
+		if mode&os.ModeSymlink != 0 {
+			if !symlinkWarningPrinted && len(o.ExecParentCmdName) > 0 {
+				fmt.Fprintf(o.IOStreams.ErrOut, "warning: file %q is a symlink, skipping (consider using \"%s exec -n %q %q -- tar cf - %q | tar xf -\")\n", destFileName, o.ExecParentCmdName, src.PodNamespace, src.PodName, src.File)
+				symlinkWarningPrinted = true
+				continue
+			}
+			fmt.Fprintf(o.IOStreams.ErrOut, "warning: skipping symlink: %q -> %q\n", destFileName, header.Linkname)
+			continue
+		}
+		outFile, err := os.Create(destFileName)
 		if err != nil {
 			return err
 		}
-		// For scrutiny we verify both the actual destination as well as we follow
-		// all the links that might lead outside of the destination directory.
-		if !isDestRelative(destDir, filepath.Join(evaledPath, filepath.Base(destFileName))) {
-			fmt.Fprintf(o.IOStreams.ErrOut, "warning: file %q is outside target destination, skipping\n", destFileName)
-			continue
+		defer outFile.Close()
+		if _, err := io.Copy(outFile, tarReader); err != nil {
+			return err
 		}
-
-		if mode&os.ModeSymlink != 0 {
-			linkname := header.Linkname
-			// We need to ensure that the link destination is always within boundries
-			// of the destination directory. This prevents any kind of path traversal
-			// from within tar archive.
-			linkTarget := linkname
-			if !filepath.IsAbs(linkname) {
-				linkTarget = filepath.Join(evaledPath, linkname)
-			}
-			if !isDestRelative(destDir, linkTarget) {
-				fmt.Fprintf(o.IOStreams.ErrOut, "warning: link %q is pointing to %q which is outside target destination, skipping\n", destFileName, header.Linkname)
-				continue
-			}
-			if err := os.Symlink(linkname, destFileName); err != nil {
-				return err
-			}
-		} else {
-			outFile, err := os.Create(destFileName)
-			if err != nil {
-				return err
-			}
-			defer outFile.Close()
-			if _, err := io.Copy(outFile, tarReader); err != nil {
-				return err
-			}
-			if err := outFile.Close(); err != nil {
-				return err
-			}
+		if err := outFile.Close(); err != nil {
+			return err
 		}
 	}
 

pkg/kubectl/cmd/cp/cp_test.go

@@ -302,11 +302,13 @@ func TestTarUntar(t *testing.T) {
 		{
 			name:     "gakki",
 			data:     "tmp/gakki",
+			omitted:  true,
 			fileType: SymLink,
 		},
 		{
 			name:     "relative_to_dest",
 			data:     path.Join(dir2, "foo"),
+			omitted:  true,
 			fileType: SymLink,
 		},
 		{
@@ -358,7 +360,7 @@ func TestTarUntar(t *testing.T) {
 	}
 
 	reader := bytes.NewBuffer(writer.Bytes())
-	if err := opts.untarAll(reader, dir2, ""); err != nil {
+	if err := opts.untarAll(fileSpec{}, reader, dir2, ""); err != nil {
 		t.Fatalf("unexpected error: %v", err)
 	}
 
@@ -419,7 +421,7 @@ func TestTarUntarWrongPrefix(t *testing.T) {
 	}
 
 	reader := bytes.NewBuffer(writer.Bytes())
-	err = opts.untarAll(reader, dir2, "verylongprefix-showing-the-tar-was-tempered-with")
+	err = opts.untarAll(fileSpec{}, reader, dir2, "verylongprefix-showing-the-tar-was-tempered-with")
 	if err == nil || !strings.Contains(err.Error(), "tar contents corrupted") {
 		t.Fatalf("unexpected error: %v", err)
 	}
@@ -534,7 +536,7 @@ func TestBadTar(t *testing.T) {
 	}
 
 	opts := NewCopyOptions(genericclioptions.NewTestIOStreamsDiscard())
-	if err := opts.untarAll(&buf, dir, "/prefix"); err != nil {
+	if err := opts.untarAll(fileSpec{}, &buf, dir, "/prefix"); err != nil {
 		t.Errorf("unexpected error: %v ", err)
 		t.FailNow()
 	}
@@ -780,35 +782,20 @@ func TestUntar(t *testing.T) {
 		expected: "",
 	}}
 
-	mkExpectation := func(expected, suffix string) string {
-		if expected == "" {
-			return ""
-		}
-		return expected + suffix
-	}
-	mkBacklinkExpectation := func(expected, suffix string) string {
-		// "resolve" the back link relative to the expectation
-		targetDir := filepath.Dir(filepath.Dir(expected))
-		// If the "resolved" target is not nested in basedir, it is escaping.
-		if !filepath.HasPrefix(targetDir, basedir) {
-			return ""
-		}
-		return expected + suffix
-	}
 	links := []file{}
 	for _, f := range files {
 		links = append(links, file{
 			path:       f.path + "-innerlink",
 			linkTarget: "link-target",
-			expected:   mkExpectation(f.expected, "-innerlink"),
+			expected:   "",
 		}, file{
 			path:       f.path + "-innerlink-abs",
 			linkTarget: filepath.Join(basedir, "link-target"),
-			expected:   mkExpectation(f.expected, "-innerlink-abs"),
+			expected:   "",
 		}, file{
 			path:       f.path + "-backlink",
 			linkTarget: filepath.Join("..", "link-target"),
-			expected:   mkBacklinkExpectation(f.expected, "-backlink"),
+			expected:   "",
 		}, file{
 			path:       f.path + "-outerlink-abs",
 			linkTarget: filepath.Join(testdir, "link-target"),
@@ -832,7 +819,7 @@ func TestUntar(t *testing.T) {
 		file{
 			path:       "nested/again/back-link",
 			linkTarget: "../../nested",
-			expected:   filepath.Join(basedir, "nested/again/back-link"),
+			expected:   "",
 		},
 		file{
 			path:     "nested/again/back-link/../../../back-link-file",
@@ -844,7 +831,7 @@ func TestUntar(t *testing.T) {
 		file{
 			path:       "nested/back-link-first",
 			linkTarget: "../",
-			expected:   filepath.Join(basedir, "nested/back-link-first"),
+			expected:   "",
 		},
 		file{
 			path:       "nested/back-link-first/back-link-second",
@@ -892,7 +879,7 @@ func TestUntar(t *testing.T) {
 	output := (*testWriter)(t)
 	opts := NewCopyOptions(genericclioptions.IOStreams{In: &bytes.Buffer{}, Out: output, ErrOut: output})
 
-	require.NoError(t, opts.untarAll(buf, filepath.Join(basedir), ""))
+	require.NoError(t, opts.untarAll(fileSpec{}, buf, filepath.Join(basedir), ""))
 
 	filepath.Walk(testdir, func(path string, info os.FileInfo, err error) error {
 		if err != nil {
@@ -943,7 +930,7 @@ func TestUntar_SingleFile(t *testing.T) {
 	output := (*testWriter)(t)
 	opts := NewCopyOptions(genericclioptions.IOStreams{In: &bytes.Buffer{}, Out: output, ErrOut: output})
 
-	require.NoError(t, opts.untarAll(buf, filepath.Join(dest), srcName))
+	require.NoError(t, opts.untarAll(fileSpec{}, buf, filepath.Join(dest), srcName))
 	cmpFileData(t, dest, content)
 }