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Message-ID: <2025031216-CVE-2025-21860-48f9@gregkh> Date: Wed, 12 Mar 2025 10:42:26 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-cve-announce@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Subject: CVE-2025-21860: mm/zswap: fix inconsistency when zswap_store_page() fails Description =========== 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@...il.com: refactor zswap_store_page()] Link: https://lkml.kernel.org/r/20250131082037.2426-1-42.hyeyoo@gmail.com The Linux kernel CVE team has assigned CVE-2025-21860 to this issue. Affected and fixed versions =========================== Issue introduced in 6.13 with commit b7c0ccdfbafdec98699ddb6f164beebf16f0bc45 and fixed in 6.13.5 with commit a3652f5552b20903315612da487a7be2b95394d5 Issue introduced in 6.13 with commit b7c0ccdfbafdec98699ddb6f164beebf16f0bc45 and fixed in 6.14-rc4 with commit 63895d20d63b446f5049a963983489319c2ea3e2 Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2025-21860 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: mm/zswap.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/a3652f5552b20903315612da487a7be2b95394d5 https://git.kernel.org/stable/c/63895d20d63b446f5049a963983489319c2ea3e2
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