CVE-2024-42234 mm: fix crashes from deferred split racing folio migration
A race condition in the Linux kernel memory management subsystem can cause crashes and double frees, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2024-42234?
CVE-2024-42234 is a high-severity vulnerability in Linux kernel, published on 7 Aug 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
mm: fix crashes from deferred split racing folio migration
Even on 6.10-rc6, I've been seeing elusive "Bad page state"s (often on flags when freeing, yet the flags shown are not bad: PG_locked had been set and cleared??), and VM_BUG_ON_PAGE(page_ref_count(page) == 0)s from deferred_split_scan()'s folio_put(), and a variety of other BUG and WARN symptoms implying double free by deferred split and large folio migration.
6.7 commit 9bcef5973e31 ("mm: memcg: fix split queue list crash when large folio migration") was right to fix the memcg-dependent locking broken in 85ce2c517ade ("memcontrol: only transfer the memcg data for migration"), but missed a subtlety of deferred_split_scan(): it moves folios to its own local list to work on them without split_queue_lock, during which time folio->_deferred_list is not empty, but even the "right" lock does nothing to secure the folio and the list it is on.
Fortunately, deferred_split_scan() is careful to use folio_try_get(): so folio_migrate_mapping() can avoid the race by folio_undo_large_rmappable() while the old folio's reference count is temporarily frozen to 0 - adding such a freeze in the !mapping case too (originally, folio lock and unmapping and no swap cache left an anon folio unreachable, so no freezing was needed there: but the deferred split queue offers a way to reach it).
Weakness: CWE-415
Which versions are affected by CVE-2024-42234?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-42234?
Apply the vendor's patch.
Is CVE-2024-42234 being exploited?
There is no known exploitation of CVE-2024-42234 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2024-42234, DEBIAN-CVE-2024-42234, GHSA-6p6f-gc59-4w3f, UBUNTU-CVE-2024-42234.