MountStubsCleaner: preserve timestamps

Fix issue 3148

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

client/client_test.go

@@ -176,6 +176,7 @@ func TestIntegration(t *testing.T) {
 		testExportAnnotationsMediaTypes,
 		testExportAttestations,
 		testAttestationDefaultSubject,
+		testMountStubsTimestamp,
 	)
 	tests = append(tests, diffOpTestCases()...)
 	integration.Run(t, tests, mirrors)
@@ -6769,6 +6770,61 @@ func testAttestationDefaultSubject(t *testing.T, sb integration.Sandbox) {
 	}
 }
 
+// https://github.com/moby/buildkit/issues/3148
+func testMountStubsTimestamp(t *testing.T, sb integration.Sandbox) {
+	c, err := New(sb.Context(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	const sourceDateEpoch = int64(1234567890) // Fri Feb 13 11:31:30 PM UTC 2009
+	st := llb.Image("busybox:latest").Run(
+		llb.Args([]string{"/bin/touch", fmt.Sprintf("--date=@%d", sourceDateEpoch), "/bin", "/etc"}),
+	)
+	def, err := st.Marshal(sb.Context())
+	require.NoError(t, err)
+
+	tmpDir := t.TempDir()
+	tarFile := filepath.Join(tmpDir, "out.tar")
+	tarFileW, err := os.Create(tarFile)
+	require.NoError(t, err)
+	defer tarFileW.Close()
+
+	_, err = c.Solve(sb.Context(), def, SolveOpt{
+		Exports: []ExportEntry{
+			{
+				Type:   ExporterTar,
+				Output: fixedWriteCloser(tarFileW),
+			},
+		},
+	}, nil)
+	require.NoError(t, err)
+	tarFileW.Close()
+
+	tarFileR, err := os.Open(tarFile)
+	require.NoError(t, err)
+	defer tarFileR.Close()
+	tarR := tar.NewReader(tarFileR)
+	touched := map[string]*tar.Header{
+		"bin/": nil,
+		"etc/": nil,
+	}
+	for {
+		hd, err := tarR.Next()
+		if errors.Is(err, io.EOF) {
+			break
+		}
+		require.NoError(t, err)
+		if x, ok := touched[hd.Name]; ok && x == nil {
+			touched[hd.Name] = hd
+		}
+	}
+	for name, hd := range touched {
+		t.Logf("Verifying %q (%+v)", name, hd)
+		require.NotNil(t, hd, name)
+		require.Equal(t, sourceDateEpoch, hd.ModTime.Unix(), name)
+	}
+}
+
 func makeSSHAgentSock(t *testing.T, agent agent.Agent) (p string, err error) {
 	tmpDir, err := integration.Tmpdir(t)
 	if err != nil {

executor/stubs.go

@@ -7,6 +7,7 @@ import (
 	"syscall"
 
 	"github.com/containerd/continuity/fs"
+	"github.com/sirupsen/logrus"
 )
 
 func MountStubsCleaner(dir string, mounts []Mount) func() {
@@ -43,7 +44,26 @@ func MountStubsCleaner(dir string, mounts []Mount) func() {
 			if st.Size() != 0 {
 				continue
 			}
-			os.Remove(p)
+			// Back up the timestamps of the dir for reproducible builds
+			// https://github.com/moby/buildkit/issues/3148
+			dir := filepath.Dir(p)
+			dirSt, err := os.Stat(dir)
+			if err != nil {
+				logrus.WithError(err).Warnf("Failed to stat %q (parent of %q)", dir, p)
+				continue
+			}
+			atime := fs.StatATimeAsTime(dirSt.Sys().(*syscall.Stat_t))
+			mtime := dirSt.ModTime()
+
+			if err := os.RemoveAll(p); err != nil {
+				logrus.WithError(err).Warnf("Failed to remove %q", p)
+				continue
+			}
+
+			// Revert the timestamps of the dir
+			if err := os.Chtimes(dir, atime, mtime); err != nil {
+				logrus.WithError(err).Warnf("Failed to os.Chtimes(%q, %v, %v)", dir, atime, mtime)
+			}
 		}
 	}
 }