PermissionError raised when fixing permissions on symlinks pointing to non-accessible file/directory

[Quentin Kaiser]

If a filesystem holds a symlink pointing to a file located within a directory the process user has no access to, an unhandled PermissionError exception will be raised and stop the extraction.

In the attached sample, the badlink file points to /etc/ssl/private/ssl-cert-snakeoil.key. This file can't be read due to permissions on /etc/ssl/private:

ls -al /etc/ssl 
total 52
drwxr-xr-x   4 root root      4096 feb 28 09:57 .
drwxr-xr-x 204 root root     12288 apr 10 14:11 ..
drwxr-xr-x   3 root root     16384 jun  8  2023 certs
-rw-r--r--   1 root root     12419 feb  6  2023 openssl.cnf
drwx--x---   2 root ssl-cert  4096 jun  8  2023 private

When calling .exists(), pathlib follows the symlink and calls stat() on the destination. Since the destination is in a directory that can't be read, the stat call fails.

One solution would be to use the follow_symlinks attribute of exists(), but it's only available since Python 3.12 so it's a no go.

Sample: sample.zip

Stack trace:

File "/home/quentin/.local/lib/python3.10/site-packages/unblob/extractor.py", line 102, in _fix_extracted_directory
    fix_permission(path)
  File "/home/quentin/.local/lib/python3.10/site-packages/unblob/extractor.py", line 26, in fix_permission
    if not path.exists():
  File "/usr/lib/python3.10/pathlib.py", line 1290, in exists
    self.stat()

[Quentin Kaiser]

It's a regression introduced by myself with 486bb91 :(