Medium [CVE-2026-74348] require a ref for locking_state debugfs open

In the Linux kernel, the following vulnerability has been resolved: ocfs2/dlm: require a ref for locking_state debugfs open debug_lockres_open() copies inode->i_private into struct debug_lockres and debug_lockres_release() later drops that pointer with dlm_put(). That only works if open successfully pins the struct dlm_ctxt.

Today open calls dlm_grab(dlm) but ignores its return value. Once the last domain unregister has removed the context from dlm_domains, dlm_grab() returns NULL, yet open still stores the raw pointer and returns success.

The later release path is outside the debugfs removal barrier, so it can call dlm_put() after dlm_free_ctxt_mem() has freed the context. KASAN reports this as a slab-use-after-free in dlm_put() called from debug_lockres_release().

Fail the open when dlm_grab() cannot acquire the reference and unwind the seq_file private state before returning. That keeps locking_state from handing out a file descriptor whose release path does not own the dlm_ctxt.

The buggy scenario involves two paths, with each column showing the order within that path: locking_state debugfs open: last domain unregister: 1. debug_lockres_open() reads 1. dlm_unregister_domain() calls inode->i_private. dlm_complete_dlm_shutdown().

2. debug_lockres_open() calls 2. shutdown removes the dlm_ctxt from dlm_grab(dlm) and gets NULL. dlm_domains.