CVE-2026-89760 in Linux
Summary
by MITRE • 09/11/2026
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. swap_put_entries_cluster() follows that rule. swap_free_hibernation_slot() does not, it calls __swap_cluster_free_entries() whether or not a folio sits on the slot.
Cluster readahead can put one there. It walks a raw page_cluster sized window of offsets around the faulting entry, and a hibernation slot passes __swap_cache_add_check() 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.
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Analysis
by VulDB Data Team • 09/12/2026
The Linux kernel contains a critical memory management vulnerability within its swap subsystem that arises from an inconsistency in how hibernation slots are handled during deallocation processes. Specifically, the function swap_free_hibernation_slot fails to adhere to the established rule that a slot containing a folio in the swap cache should not be freed until the folio actually leaves the cache. While other functions such as swap_put_entries_cluster correctly check for the presence of a cached folio before proceeding with deallocation, swap_free_hibernation_slot indiscriminately calls __swap_cluster_free_entries regardless of whether a folio is currently associated with the slot. This deviation from standard protocol creates a race condition where the underlying storage entry can be cleared while it remains actively referenced by system memory structures, leading to severe integrity violations within the kernel's virtual memory management layer.
The operational mechanism triggering this flaw involves cluster readahead operations which scan a window of offsets around a faulting page and may add hibernation slots to the swap cache via __swap_cache_add_check. Because these slots are not treated as standard folios during initial checks, they pass validation despite having non-zero reference counts or cached states. When the flawed deallocation path is executed, it clears the swap entry associated with that slot while the corresponding folio remains resident in memory and on the Least Recently Used list for page reclaim. This creates a state where the physical storage location has been marked as free and available for reallocation, yet the kernel still holds an active reference to data residing at that logical offset through the lingering folio structure.
This inconsistency leads directly to silent memory corruption because subsequent operations may reuse the freed slot's offset for entirely different purposes without realizing that existing data structures are still pointing to it. As page reclaim mechanisms eventually process the orphaned folio, they attempt to update or access swap information using offsets that no longer correspond to their original intended targets. The result is a high probability of overwriting critical kernel data structures with unrelated user space application data or system metadata. This corruption manifests unpredictably as process crashes, data instability across unrelated applications, and potential privilege escalation vectors if the corrupted memory regions include security-critical controls such as access control lists or execution permissions.
From a threat modeling perspective, this vulnerability aligns with CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization, specifically involving race conditions in resource deallocation logic. It also relates to CWE-416 Use After Free, where the system maintains references to memory resources that have been logically freed and potentially reallocated for other purposes. In terms of MITRE ATT&CK frameworks, this flaw could be leveraged by an attacker with local access to induce denial of service through kernel panics or facilitate lateral movement via privilege escalation if the corruption affects security boundaries within the kernel space. The impact is particularly severe because it occurs during hibernation preparation using tools like uswsusp, a context where system stability is paramount and debugging complex memory state inconsistencies is difficult due to the low-level nature of power management operations.
The resolution involves modifying swap_free_hibernation_slot to perform an explicit check for cached folios before initiating any deallocation procedures. By ensuring that slots are only freed when they are truly detached from active caching mechanisms, the kernel maintains consistency between its logical accounting and physical memory state. This fix ensures that hibernation slots remain in a standard operational state where their lifecycle is tied strictly to the presence of associated folios in the swap cache. Consequently, these resources will be properly reclaimed only after page reclaim processes have fully processed and removed them from active lists, thereby preventing premature invalidation of valid memory references. This correction restores integrity to the swap subsystem's resource management logic and eliminates the risk of silent corruption during hibernation workflows.