CVE-2026-43389
Description
In the Linux kernel, the following vulnerability has been resolved:
mm: memfd_luo: always dirty all folios
A dirty folio is one which has been written to. A clean folio is its opposite. Since a clean folio has no user data, it can be freed under memory pressure.
memfd preservation with LUO saves the flag at preserve(). This is problematic. The folio might get dirtied later. Saving it at freeze() also doesn't work, since the dirty bit from PTE is normally synced at unmap and there might still be mappings of the file at freeze().
To see why this is a problem, say a folio is clean at preserve, but gets dirtied later. The serialized state of the folio will mark it as clean. After retrieve, the next kernel will see the folio as clean and might try to reclaim it under memory pressure. This will result in losing user data.
Mark all folios of the file as dirty, and always set the MEMFD_LUO_FOLIO_DIRTY flag. This comes with the side effect of making all clean folios un-reclaimable. This is a cost that has to be paid for participants of live update. It is not expected to be a common use case to preserve a lot of clean folios anyway.
Since the value of pfolio->flags is a constant now, drop the flags variable and set it directly.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
A Linux kernel memfd_luo bug could cause data loss during live update by incorrectly marking dirty folios as clean, fixed by always dirtying all folios.
Vulnerability
The Linux kernel's memfd_luo feature, used for live update of memory file descriptors, contains a flaw in how it tracks dirty folios. During preservation for live update, the dirty flag is saved but folios may be dirtied later, resulting in a serialized state that marks them as clean. After retrieval, the kernel may reclaim these clean folios under memory pressure, leading to data loss.
Exploitation
Exploitation requires a live update scenario where memfd preservation occurs. No special privileges are needed beyond what is required for live update operations. An attacker could induce memory pressure after retrieval to trigger reclamation of the incorrectly marked clean folios, causing loss of user data.
Impact
Successful exploitation results in loss of user data when the kernel frees folios that are actually dirty. This undermines the integrity of data preserved across live updates.
Mitigation
The fix is committed in the Linux kernel stable tree (commit e901c871d4b5) [1]. Users should apply the update to ensure all folios are marked dirty (MEMFD_LUO_FOLIO_DIRTY flag), preventing erroneous reclamation.
AI Insight generated on May 18, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
1Patches
0No patches discovered yet.
Vulnerability mechanics
AI mechanics synthesis has not run for this CVE yet.
References
2News mentions
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