CVE-2024-41034 nilfs2: fix kernel bug on rename operation of broken directory

In the Linux kernel, the following vulnerability has been resolved:

nilfs2: fix kernel bug on rename operation of broken directory

Syzbot reported that in rename directory operation on broken directory on
nilfs2, __block_write_begin_int() called to prepare block write may fail
BUG_ON check for access exceeding the folio/page size.

This is because nilfs_dotdot(), which gets parent directory reference
entry (“…”) of the directory to be moved or renamed, does not check
consistency enough, and may return location exceeding folio/page size for
broken directories.

Fix this issue by checking required directory entries (“.” and “…”) in
the first chunk of the directory in nilfs_dotdot().