CVE-2026-31466 mm/huge_memory: fix folio isn't locked in softleaf_to_folio()
A race condition in the Linux kernel memory management subsystem can cause a kernel warning or crash due to missing memory barriers during huge page splitting.
- 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-2026-31466?
CVE-2026-31466 is a medium-severity vulnerability in Linux kernel, published on 22 Apr 2026. 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/huge_memory: fix folio isn't locked in softleaf_to_folio()
On arm64 server, we found folio that get from migration entry isn't locked in softleaf_to_folio(). This issue triggers when mTHP splitting and zap_nonpresent_ptes() races, and the root cause is lack of memory barrier in softleaf_to_folio(). The race is as follows:
CPU0 CPU1
deferred_split_scan() zap_nonpresent_ptes() lock folio split_folio() unmap_folio() change ptes to migration entries __split_folio_to_order() softleaf_to_folio() set flags(including PG_locked) for tail pages folio = pfn_folio(softleaf_to_pfn(entry)) smp_wmb() VM_WARN_ON_ONCE(!folio_test_locked(folio)) prep_compound_page() for tail pages
In __split_folio_to_order(), smp_wmb() guarantees page flags of tail pages are visible before the tail page becomes non-compound. smp_wmb() should be paired with smp_rmb() in softleaf_to_folio(), which is missed. As a result, if zap_nonpresent_ptes() accesses migration entry that stores tail pfn, softleaf_to_folio() may see the updated compound_head of tail page before page->flags.
This issue will trigger VM_WARN_ON_ONCE() in pfn_swap_entry_folio() because of the race between folio split and zap_nonpresent_ptes() leading to a folio incorrectly undergoing modification without a folio lock being held.
This is a BUG_ON() before commit 93976a20345b ("mm: eliminate further swapops predicates"), which in merged in v6.19-rc1.
To fix it, add missing smp_rmb() if the softleaf entry is migration entry in softleaf_to_folio() and softleaf_to_page().
[[email protected]: update function name and comments]
Weakness: CWE-362
Which versions are affected by CVE-2026-31466?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31466?
Apply the vendor's patch.
Is CVE-2026-31466 being exploited?
There is no known exploitation of CVE-2026-31466 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31466, DEBIAN-CVE-2026-31466, GHSA-j7cp-5j3g-7q5w, ROOT-OS-DEBIAN-11-CVE-2026-31466, ROOT-OS-UBUNTU-2204-CVE-2026-31466, ROOT-OS-UBUNTU-2404-CVE-2026-31466 and 1 more.