Fix #940 set modtime when extracting

Certain utilities like Apt depend on modtime
for certain files. Kaniko was not setting modtime when
extracting files and so this broke things like apt.

Kaniko now sets the file mod time to the value from the tar
header.

pkg/util/fs_util.go

@@ -215,6 +215,7 @@ func ExtractFile(dest string, hdr *tar.Header, tr io.Reader) error {
 	switch hdr.Typeflag {
 	case tar.TypeReg:
 		logrus.Tracef("creating file %s", path)
+
 		// It's possible a file is in the tar before its directory,
 		// or a file was copied over a directory prior to now
 		fi, err := os.Stat(dir)
@@ -225,6 +226,7 @@ func ExtractFile(dest string, hdr *tar.Header, tr io.Reader) error {
 				return err
 			}
 		}
+
 		// Check if something already exists at path (symlinks etc.)
 		// If so, delete it
 		if FilepathExists(path) {
@@ -232,16 +234,26 @@ func ExtractFile(dest string, hdr *tar.Header, tr io.Reader) error {
 				return errors.Wrapf(err, "error removing %s to make way for new file.", path)
 			}
 		}
+
 		currFile, err := os.Create(path)
 		if err != nil {
 			return err
 		}
+
 		if _, err = io.Copy(currFile, tr); err != nil {
 			return err
 		}
+
 		if err = setFilePermissions(path, mode, uid, gid); err != nil {
 			return err
 		}
+
+		// We set AccessTime because its a required arg but we only care about
+		// ModTime. The file will get accessed again so AccessTime will change.
+		if err := os.Chtimes(path, hdr.AccessTime, hdr.ModTime); err != nil {
+			return err
+		}
+
 		currFile.Close()
 	case tar.TypeDir:
 		logrus.Tracef("creating dir %s", path)
@@ -647,6 +659,7 @@ func mkdirAllWithPermissions(path string, mode os.FileMode, uid, gid int) error
 	if err := os.MkdirAll(path, mode); err != nil {
 		return err
 	}
+
 	if err := os.Chown(path, uid, gid); err != nil {
 		return err
 	}