CVE-2026-74348 in Linux
Summary
by MITRE • 08/15/2026
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. 3. open still stores the raw dlm 3. final teardown reaches pointer in dl->dl_ctxt and dlm_free_ctxt_mem() and frees it. returns success. 4. debug_lockres_release() later calls dlm_put(dl->dl_ctxt).
Validation reproduced this kernel report: KASAN slab-use-after-free in dlm_put+0x82/0x200 RIP: 0033:0x7f4d349bc9e0 The buggy address belongs to the object at ffff888103a3c000 which belongs to the cache kmalloc-2k of size 2048 The buggy address is located 816 bytes inside of freed 2048-byte region [ffff888103a3c000, ffff888103a3c800)
Write of size 4 Call trace: dump_stack_lvl+0x66/0xa0 (?:?) print_report+0xd0/0x630 (?:?) dlm_put+0x82/0x200 (?:?) srso_alias_return_thunk+0x5/0xfbef5 (?:?) __virt_addr_valid+0x188/0x2f0 (?:?) kasan_report+0xe4/0x120 (?:?) kasan_check_range+0x105/0x1b0 (?:?) debug_lockres_release+0x53/0x80 (fs/ocfs2/dlm/dlmdebug.c:587) dlm_put+0x9/0x200 (?:?) debug_lockres_release+0x5c/0x80 (fs/ocfs2/dlm/dlmdebug.c:587) full_proxy_release+0x67/0x90 (?:?) __fput+0x1df/0x4b0 (?:?) do_raw_spin_lock+0x10f/0x1b0 (?:?) fput_close_sync+0xd2/0x170 (?:?) __x64_sys_close+0x55/0x90 (?:?) do_syscall_64+0x10c/0x640 (arch/x86/entry/syscall_64.c:87) irqentry_exit+0xac/0x6e0 (?:?) entry_SYSCALL_64_after_hwframe+0x77/0x7f (?:?) Freed by task stack: kasan_save_stack+0x33/0x60 (?:?) kasan_save_track+0x14/0x30 (?:?) kasan_save_free_info+0x3b/0x60 (?:?) __kasan_slab_free+0x5f/0x80 (?:?) kfree+0x30f/0x580 (?:?) dlm_put+0x1ce/0x200 (?:?) dlm_unregister_domain+0xf6/0xb30 (?:?) o2cb_cluster_disconnect+0x6b/0x90 (?:?) ocfs2_cluster_disconnect+0x41/0x70 (?:?) ocfs2_dlm_shutdown+0x1c4/0x220 (?:?) ocfs2_dismount_volume+0x38a/0x550 (?:?) generic_shutdown_super+0xc3/0x220 (?:?) kill_block_super+0x29/0x60 (?:?) deactivate_locked_super+0x66/0xe0 (?:?) cleanup_mnt+0x13d/0x210 (?:?) task_work_run+0xfa/0x170 (?:?) exit_to_user_mode_loop+0xd6/0x430 (?:?) do_syscall_64+0x3cb/0x640 (arch/x86/entry/syscall_64.c:87) entry_SYSCALL_64_after_hwframe+0x77/0x7f (?:?)
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability described in this CVE relates to a use-after-free condition in the Linux kernel's ocfs2 distributed lock manager implementation, specifically within the debugfs interface for locking state. This flaw occurs when a debugfs file is opened to access locking information while a domain unregister operation is concurrently occurring, leading to improper reference counting and subsequent memory corruption. The root cause lies in the `debug_lockres_open()` function which calls `dlm_grab(dlm)` but fails to properly validate its return value. When a domain has been unregistered and removed from the dlm_domains list, `dlm_grab()` returns NULL indicating it cannot acquire the necessary reference, yet the open operation continues to store this invalid pointer and proceeds with success.
The technical execution path demonstrates a classic race condition where the debugfs open handler does not properly synchronize with domain shutdown operations. During normal operation, `debug_lockres_open()` copies `inode->i_private` into a `struct debug_lockres` and stores a pointer to the dlm context. However, when `dlm_grab()` fails to acquire a reference due to the context being in the process of teardown, the function still proceeds to store the raw pointer without checking for failure. The subsequent `debug_lockres_release()` function then attempts to call `dlm_put()` on this invalid pointer after the memory has already been freed by `dlm_free_ctxt_mem()`, resulting in a slab-use-after-free error.
This vulnerability directly maps to CWE-415: Double Free and CWE-416: Use After Free, as it involves accessing freed memory through improper reference handling. The flaw is particularly dangerous because it can be exploited to cause system instability or potentially enable privilege escalation if an attacker can orchestrate the timing of domain unregister operations with debugfs access. From an ATT&CK perspective, this represents a kernel-level exploitation vector that could be leveraged for privilege escalation or denial of service attacks, specifically under the techniques category of privilege escalation through kernel exploits.
The mitigation strategy requires modifying `debug_lockres_open()` to properly check the return value of `dlm_grab()` and fail the open operation when it cannot acquire a valid reference. This involves ensuring that if `dlm_grab()` returns NULL, the function should immediately unwind any allocated seq_file private state before returning an error code. This prevents the debugfs interface from handing out file descriptors whose release path would attempt to operate on freed memory. The fix ensures proper reference counting and maintains synchronization between domain registration/unregistration operations and debugfs access paths, preventing the race condition that leads to memory corruption.