SaveFile: respect umask for final file mode, fixes #6400

src/borg/platform/base.py

@@ -4,6 +4,7 @@ import socket
 import tempfile
 import uuid
 
+from borg.constants import UMASK_DEFAULT
 from borg.helpers import safe_unlink
 
 """
@@ -193,6 +194,15 @@ class SaveFile:
         if exc_type is not None:
             safe_unlink(self.tmp_fname)  # with-body has failed, clean up tmp file
             return  # continue processing the exception normally
+
+        # tempfile.mkstemp always uses owner-only file permissions for the temp file,
+        # but as we'll rename it to the non-temp permanent file now, we need to respect
+        # the umask and change the file mode to what a normally created file would have.
+        # thanks to the crappy os.umask api, we can't query the umask without setting it. :-(
+        umask = os.umask(UMASK_DEFAULT)
+        os.umask(umask)
+        os.chmod(self.tmp_fname, mode=0o666 & ~ umask)
+
         try:
             os.replace(self.tmp_fname, self.path)  # POSIX: atomic rename
         except OSError: