CVE-2026-89961 powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population
Incorrect PFN tracking in PowerPC memory management can lead to improper head/tail page mapping decisions, potentially causing memory corruption or instability.
- 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-2026-89961?
CVE-2026-89961 is a high-severity vulnerability in Linux, published on 16 Sep 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:
powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population
vmemmap_populate_compound_pages() uses addr_pfn to determine the PFN offset within a compound page and to decide whether the current vmemmap slot should be populated as a head page mapping or should reuse a tail page mapping.
However, addr_pfn is advanced manually in parallel with addr. The loop itself progresses in vmemmap address space, so each PAGE_SIZE step in addr covers PAGE_SIZE / sizeof(struct page) struct page slots. Since addr_pfn is compared against nr_pages in data-PFN units, it should advance by the same number of PFNs. The existing manual increments do not match that and therefore do not reliably track the PFN corresponding to the current addr.
As a result, pfn_offset can be computed from the wrong PFN and the code can make the head/tail decision for the wrong compound-page position.
Fix this by deriving addr_pfn directly from the current vmemmap address instead of carrying it as loop state.
Which versions are affected by CVE-2026-89961?
How do I fix CVE-2026-89961?
Apply the vendor's patch.
Is CVE-2026-89961 being exploited?
There is no known exploitation of CVE-2026-89961 in the wild and no public exploit code.
Sources
Also known as AZL-101217, BELL-CVE-2026-89961, DEBIAN-CVE-2026-89961, GHSA-25fw-r826-pmc4, UBUNTU-CVE-2026-89961.