kconfig: kconfiglib.py: Backup files only

The _save_old() to return early if <filename> is not file (or symlink
to a file).

This is simplest alternative to avoid attempt to rename /dev/null
(which could succeed).

This also keeps fifos (perhaps nonexistent potential usage but
this is nicer).

If <filename> were directory or socket, after shutil.copyfile(),
writing to the file (by caller, _write_config()), would fail.

Fixes #31362

Co-authored-by: Marti Bolivar <[email protected]>
Signed-off-by: Tomi Ollila <[email protected]>

Author: 2 people

scripts/kconfig/kconfiglib.py

@@ -1545,8 +1545,7 @@ def write_config(self, filename=None, header=None, save_old=True,
           written.
 
           Errors are silently ignored if <filename>.old cannot be written (e.g.
-          due to being a directory, or <filename> being something like
-          /dev/null).
+          due to permissions errors).
 
         verbose (default: None):
           Limited backwards compatibility to prevent crashes. A warning is
@@ -6392,6 +6391,12 @@ def _touch_dep_file(path, sym_name):
 def _save_old(path):
     # See write_config()
 
+    if not os.path.isfile(path):
+        # Backup only files (and symlinks to files). Simplest alternative
+        # to avoid e.g. (potentially successful attempt to) rename /dev/null
+        # (and to keep fifos).
+        return
+
     def copy(src, dst):
         # Import as needed, to save some startup time
         import shutil
@@ -6416,8 +6421,7 @@ def copy(src, dst):
     except Exception:
         # Ignore errors from 'path' missing as well as other errors.
         # <filename>.old file is usually more of a nice-to-have, and not worth
-        # erroring out over e.g. if <filename>.old happens to be a directory or
-        # <filename> is something like /dev/null.
+        # erroring out over e.g. if <filename>.old happens to be a directory.
         pass