feat: host builder nonregular file support

pkg/oci/containerize.go

@@ -7,13 +7,13 @@ import (
 	"fmt"
 	"io"
 	"os"
-	slashpath "path"
 	"path/filepath"
 	"strings"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/tarball"
 	"github.com/google/go-containerregistry/pkg/v1/types"
+	"github.com/pkg/errors"
 )
 
 // languageLayerBuilder builds the layer for the given language whuch may
@@ -136,6 +136,8 @@ func newDataTarball(source, target string, ignored []string, verbose bool) error
 	tw := tar.NewWriter(gw)
 	defer tw.Close()
 
+	baseDir := "/func"
+
 	return filepath.Walk(source, func(path string, info os.FileInfo, err error) error {
 		if err != nil {
 			return err
@@ -150,27 +152,32 @@ func newDataTarball(source, target string, ignored []string, verbose bool) error
 			}
 		}
 
-		header, err := tar.FileInfoHeader(info, info.Name())
-		if err != nil {
-			return err
+		var link string
+		if info.Mode()&os.ModeSymlink == os.ModeSymlink {
+			if link, err = os.Readlink(path); err != nil {
+				return err
+			}
+			ok, err := isWithin(source, link)
+			if err != nil {
+				return errors.Wrap(err, "error checking if link is outside function root")
+			} else if !ok {
+				return fmt.Errorf("links outside Function root disallowed.  Link %v references %v", path, link)
+			}
 		}
 
-		relPath, err := filepath.Rel(source, path)
+		header, err := tar.FileInfoHeader(info, link)
 		if err != nil {
 			return err
 		}
 
-		header.Name = slashpath.Join("/func", filepath.ToSlash(relPath))
-		// TODO: should we set file timestamps to the build start time of cfg.t?
-		// header.ModTime = timestampArgument
-
-		if err := tw.WriteHeader(header); err != nil {
+		header.Name = filepath.Join(baseDir, strings.TrimPrefix(path, source))
+		if err = tw.WriteHeader(header); err != nil {
 			return err
 		}
 		if verbose {
 			fmt.Printf("→ %v \n", header.Name)
 		}
-		if info.IsDir() {
+		if !info.Mode().IsRegular() { //nothing more to do for non-regular
 			return nil
 		}
 
@@ -185,6 +192,27 @@ func newDataTarball(source, target string, ignored []string, verbose bool) error
 	})
 }
 
+// isWithin returns true if the parent path has the child path within.
+// If parent and child are the same target, this is considered within.
+func isWithin(parent, child string) (bool, error) {
+	var err error
+	// Convert the paths to clean absolute paths.
+	if parent, err = filepath.Abs(filepath.Clean(parent)); err != nil {
+		return false, err
+	}
+	if child, err = filepath.Abs(filepath.Clean(child)); err != nil {
+		return false, err
+	}
+	// Calculate the relative path between them
+	relPath, err := filepath.Rel(parent, child)
+	if err != nil {
+		return false, err
+	}
+	// Child is not within parent if the relative path from parent to child
+	// requires ..
+	return !strings.HasPrefix(relPath, ".."), nil
+}
+
 // newCertLayer creates the shared data layer in the container file hierarchy and
 // returns both its descriptor and layer metadata.
 func newCertsLayer(cfg *buildConfig) (desc v1.Descriptor, layer v1.Layer, err error) {

pkg/oci/containerize_test.go

@@ -0,0 +1,34 @@
+package oci
+
+import "testing"
+
+// Test_isWithin ensures that the isWithin method checks
+// that various combinations of parent and child paths.
+func Test_isWithin(t *testing.T) {
+	tests := []struct {
+		parent string
+		child  string
+		want   bool
+		name   string
+	}{
+		{"/", "/b", true, "Base case, a subdir of an absolute path"},
+		{"/a", "/ab", false, "Ensure simple substring does not match"},
+		{"./", ".", true, "Ensure links are both made absolute"},
+		{"/a/b/../c", "/a/c/d/../", true, "Ensure the links are both sanitized"},
+		{"/a", "/a/b/../../", false, "Ensure escaping the parent is a mismatch"},
+		{"./", "../", false, "Ensure simple relative mismatch"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := isWithin(tt.parent, tt.child)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got != tt.want {
+				t.Log(tt.name)
+				t.Errorf("isWithin() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+
+}