isofs: validate directory records consistently

isofs_export_get_parent() assumes that the first two directory records
are valid "." and ".." entries.  A malformed image can provide an
invalid length for the first entry, causing the computed ".." offset to
point outside the received block.

Add a shared directory record validator and use it in NFS get_parent,
readdir and lookup.  This keeps the basic directory record length checks
consistent across all directory users before they consume the name field
or use one record length to find the next entry.

Signed-off-by: Yichong Chen <chenyichong@uniontech.com>
Link: https://patch.msgid.link/20260728074349.417508-1-chenyichong@uniontech.com
Signed-off-by: Jan Kara <jack@suse.cz>

0 files changed, 0 insertions, 0 deletions