lib/pull: Check whether summary is in normal form when loading it

Check that it’s in normal form and has the correct type when loading it,
since it could come from an untrusted source.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #961
Approved by: cgwalters

src/libostree/ostree-repo-pull.c

@@ -3362,6 +3362,20 @@ ostree_repo_pull_with_options (OstreeRepo             *self,
         pull_data->summary_data = g_bytes_ref (bytes_summary);
         pull_data->summary = g_variant_new_from_bytes (OSTREE_SUMMARY_GVARIANT_FORMAT, bytes_summary, FALSE);
 
+        if (!g_variant_is_normal_form (pull_data->summary))
+          {
+            g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                                 "Not normal form");
+            goto out;
+          }
+        if (!g_variant_is_of_type (pull_data->summary, OSTREE_SUMMARY_GVARIANT_FORMAT))
+          {
+            g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                         "Doesn't match variant type '%s'",
+                         (char *)OSTREE_SUMMARY_GVARIANT_FORMAT);
+            goto out;
+          }
+
         if (bytes_sig)
           pull_data->summary_data_sig = g_bytes_ref (bytes_sig);
       }