Linux Kernel
CVE-2025-21860
LOW
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Lifecycle Timeline
3DescriptionCVE.org
In the Linux kernel, the following vulnerability has been resolved:
mm/zswap: fix inconsistency when zswap_store_page() fails
Commit b7c0ccdfbafd ("mm: zswap: support large folios in zswap_store()") skips charging any zswap entries when it failed to zswap the entire folio.
However, when some base pages are zswapped but it failed to zswap the entire folio, the zswap operation is rolled back. When freeing zswap entries for those pages, zswap_entry_free() uncharges the zswap entries that were not previously charged, causing zswap charging to become inconsistent.
This inconsistency triggers two warnings with following steps:
On a machine with 64GiB of RAM and 36GiB of zswap
$ stress-ng --bigheap 2
wait until the OOM-killer kills stress-ng
$ sudo reboot
The two warnings are: in mm/memcontrol.c:163, function obj_cgroup_release(): WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1));
in mm/page_counter.c:60, function page_counter_cancel(): if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n", new, nr_pages))
zswap_stored_pages also becomes inconsistent in the same way.
As suggested by Kanchana, increment zswap_stored_pages and charge zswap entries within zswap_store_page() when it succeeds. This way, zswap_entry_free() will decrement the counter and uncharge the entries when it failed to zswap the entire folio.
While this could potentially be optimized by batching objcg charging and incrementing the counter, let's focus on fixing the bug this time and leave the optimization for later after some evaluation.
After resolving the inconsistency, the warnings disappear.
[42.hyeyoo@gmail.com: refactor zswap_store_page()]
AnalysisAI
In the Linux kernel, the following vulnerability has been resolved: mm/zswap: fix inconsistency when zswap_store_page() fails Commit b7c0ccdfbafd ("mm: zswap: support large folios in zswap_store()"). Rated low severity (CVSS 3.3), this vulnerability is low attack complexity.
Technical ContextAI
In the Linux kernel, the following vulnerability has been resolved: mm/zswap: fix inconsistency when zswap_store_page() fails Commit b7c0ccdfbafd ("mm: zswap: support large folios in zswap_store()") skips charging any zswap entries when it failed to zswap the entire folio. However, when some base pages are zswapped but it failed to zswap the entire folio, the zswap operation is rolled back. When freeing zswap entries for those pages, zswap_entry_free() uncharges the zswap entries that were not previously charged, causing zswap charging to become inconsistent. This inconsistency triggers two warnings with following steps:
On a machine with 64GiB of RAM and 36GiB of zswap $ stress-ng --bigheap 2
wait until the OOM-killer kills stress-ng $ sudo reboot The two warnings are: in mm/memcontrol.c:163, function obj_cgroup_release(): WARN_ON_ONCE(nr_bytes & (PAGE_SIZE - 1)); in mm/page_counter.c:60, function page_counter_cancel(): if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n", new, nr_pages)) zswap_stored_pages also becomes inconsistent in the same way. As suggested by Kanchana, increment zswap_stored_pages and charge zswap entries within zswap_store_page() when it succeeds. This way, zswap_entry_free() will decrement the counter and uncharge the entries when it failed to zswap the entire folio. While this could potentially be optimized by batching objcg charging and incrementing the counter, let's focus on fixing the bug this time and leave the optimization for later after some evaluation. After resolving the inconsistency, the warnings disappear. [42.hyeyoo@gmail.com: refactor zswap_store_page()] Affected products include: Linux Linux Kernel.
RemediationAI
A vendor patch is available. Apply the latest security update as soon as possible. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.
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