Add subdir for tar files in the working dir

The safeguard of adding a subdir based on the first part of the
file name is necessary for docker-like image tar archives,
which don't have a folder for each layer but rather another tar.gz
file or similar. This is the case for kaniko built docker image
archives.

Without it, tar archives will overwrite the untar_dir on every new
layer analyzed. This will result in the os-release file not being
found as the os analyzer expects the files of the first layer
in the dir but it's actually the files of the last dir.

This patch is enabling a way for using Tern with kaniko images.
See tern-tools#361

Signed-off-by: Roger Lehmann <[email protected]>

Author: Roger Lehmann

tern/classes/image_layer.py

@@ -318,8 +318,18 @@ def get_untar_dir(self):
         """Get the directory where contents of the image layer are untarred"""
         # the untar directory is based on the image layout
         if self.image_layout == 'docker':
+            # Images built with Kaniko and its tarPath parameter identify
+            # as Docker image based on the metadata format, but keep their
+            # layer tar files in the root of the main tar file.
+            # So we will make sure if there's no subdir for the layer tar
+            # files, we use the first part of the file name as dir name.
+            # This is to prevent overwriting the extracted layers on every
+            # subsequent layer inspection.
+            subdir_name = os.path.dirname(self.tar_file)
+            if not subdir_name:
+                subdir_name = self.tar_file.split('.', 1)[0]
             return os.path.join(rootfs.get_working_dir(),
-                                os.path.dirname(self.tar_file),
+                                subdir_name,
                                 constants.untar_dir)
         # For OCI layouts, the tar file may be at the root of the directory
         # So we will return a path one level deeper

tests/test_class_image_layer.py

@@ -165,6 +165,12 @@ def testGetUntarDir(self):
         expected_path = os.path.join(rootfs.get_working_dir(),
                                      'path/to/contents')
         self.assertEqual(self.layer.get_untar_dir(), expected_path)
+        # Kaniko image format test
+        self.layer = ImageLayer('123abc', 'some_layer_tar_file.tar.gz')
+        self.layer.image_layout = "docker"
+        expected_path = os.path.join(rootfs.get_working_dir(),
+                                     'some_layer_tar_file/contents')
+        self.assertEqual(self.layer.get_untar_dir(), expected_path)
 
 
 if __name__ == '__main__':