run_pytest: port fs check over from run_tests

BUG=None
TEST=CQ passes

Change-Id: I9afcbf86e82a6d16992209cdaf897727698c376f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2805993
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Sergey Frolov <sfrolov@google.com>
Commit-Queue: Sergey Frolov <sfrolov@google.com>
diff --git a/scripts/run_pytest.py b/scripts/run_pytest.py
index 0420b1a..8695a62 100644
--- a/scripts/run_pytest.py
+++ b/scripts/run_pytest.py
@@ -52,6 +52,17 @@
     # Disabling namespaces is not recommended for general use.
     re_execute_with_namespace([sys.argv[0]] + argv)
 
+  # Check the environment.  https://crbug.com/1015450
+  st = os.stat('/')
+  if st.st_mode & 0o7777 != 0o755:
+    cros_build_lib.Die(
+        f'The root directory has broken permissions: {st.st_mode:o}\n'
+        'Fix with: sudo chmod 755 /')
+  if st.st_uid or st.st_gid:
+    cros_build_lib.Die(
+        f'The root directory has broken ownership: {st.st_uid}:{st.st_gid}'
+        ' (should be 0:0)\nFix with: sudo chown 0:0 /')
+
   sys.exit(pytest.main(pytest_args))