Make code to deal with overlayfs "work" directory more robust

The work directory can be populated if files are deleted in the
upperdir. In that case we need to acquire privileges to be able to
delete the directory so add a fallback for that scenario.

diff --git a/mkosi/run.py b/mkosi/run.py
index 73d15e21110b7240ad2b621f4fbe1f82eae92ac4..1b4c8398a9b9446418bccbffe38311e139cffc31 100644 (file)
--- a/mkosi/run.py
+++ b/mkosi/run.py
@@ -24,7 +24,7 @@ from typing import Any, Callable, NoReturn, Optional, Protocol
 
 import mkosi.sandbox
 from mkosi.log import ARG_DEBUG, ARG_DEBUG_SHELL, die
-from mkosi.sandbox import joinpath, umask
+from mkosi.sandbox import acquire_privileges, joinpath, umask
 from mkosi.types import _FILE, CompletedProcess, PathString, Popen
 from mkosi.util import current_home_dir, flatten, one_zero
 
@@ -435,11 +435,23 @@ def vartmpdir() -> Iterator[Path]:
         # A directory that's used as an overlayfs workdir will contain a "work" subdirectory after the overlayfs is
         # unmounted. This "work" subdirectory will have permissions 000 and as such can't be opened or searched unless
         # the user has the CAP_DAC_OVERRIDE capability. shutil.rmtree() will try to search the "work" subdirectory to
-        # remove anything in it which will fail with a permission error. To circumvent this, let's delete the "work"
-        # subdirectory first and then invoke shutil.rmtree(). Deleting the subdirectory is not a problem because
-        # deleting a subdirectory depends on the permissions of the parent directory and not the directory itself.
-        if (d / "work").exists():
+        # remove anything in it which will fail with a permission error. To circumvent this, if the work directory
+        # exists and is not empty, let's fork off a subprocess where we acquire extra privileges and then invoke
+        # shutil.rmtree(). If the work directory exists but is empty, let's just delete the "work" subdirectory first
+        # and then invoke shutil.rmtree(). Deleting the subdirectory when it is empty is not a problem because deleting
+        # a subdirectory depends on the permissions of the parent directory and not the directory itself.
+        try:
             (d / "work").rmdir()
+        except OSError as e:
+            if e.errno == errno.ENOTEMPTY:
+                def remove() -> None:
+                    acquire_privileges()
+                    shutil.rmtree(d)
+
+                fork_and_wait(remove)
+                return
+            elif e.errno != errno.ENOENT:
+                raise
 
         shutil.rmtree(d)