CVE-2026-89760: mm, swap: don't free a hibernation slot that is in the swap cache
In the Linux kernel, the following vulnerability has been resolved:
mm, swap: don't free a hibernation slot that is in the swap cache
A slot with a folio in the swap cache is freed when the folio leaves the cache, not when its count drops. swapputentriescluster() follows that rule. swapfreehibernationslot() does not, it calls swapclusterfreeentries() whether or not a folio sits on the slot.
Cluster readahead can put one there. It walks a raw pagecluster sized window of offsets around the faulting entry, and a hibernation slot passes swapcacheaddcheck() because it is not a folio and its count is not zero. Freeing the slot then clears the entry under that folio.
The folio is now unreachable from the swap table, and the offset goes back to the allocator. The folio is still on the LRU though, so reclaim can pick it up later. It then takes the old offset out of folio->swap and overwrites the table entry there, which by then may belong to someone else.
This bug can trigger silent memory corruption, process crashes, or data instability across completely unrelated userspace applications - typically occurring when uswsusp is preparing the hibernation image.
I found this while working on giving hibernation slots their own marker in the swap table, which I had discussed with Kairui. (https://lore.kernel.org/linux-mm/abp7aDgYLrxF3Me8@KASONG-MC4/) As far as I know there are no reports, so there is no Reported-by/Closes to add.
Check for a cached folio before freeing. The slot is then left in the ordinary state where only the swap cache holds it, and it is freed when the folio leaves the cache, either through the reclaim below or through normal reclaim later.
Affected Software
Event History
Frequently Asked Questions
Which systems are most likely to encounter this issue?
Systems using Linux swap and preparing a hibernation image with uswsusp are the described exposure scenario. The failure depends on cluster readahead placing a folio in the swap cache for a hibernation slot.
What operational impact can indicate this condition?
The issue can cause silent memory corruption, process crashes, or data instability affecting unrelated userspace applications. It is typically observed while uswsusp is preparing the hibernation image.
How can maintainers check for the available fix without relying on a version number?
Review whether the kernel source includes the changes referenced by stable commits a6df73156f2d85746c69adbf13d0f5ea200e0626 or 10d9012e83efedde8718ceaa5053f836e0c8596c. The provided data does not identify affected or fixed kernel release versions.