Bug 2525450 (CVE-2026-80719)
| Summary: | CVE-2026-80719 kernel: mm: mglru: fix stale batch updates after memcg reparenting | ||
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| Product: | [Other] Security Response | Reporter: | OSIDB Bzimport <bzimport> |
| Component: | vulnerability | Assignee: | Product Security DevOps Team <prodsec-dev> |
| Status: | NEW --- | QA Contact: | |
| Severity: | medium | Docs Contact: | |
| Priority: | medium | ||
| Version: | unspecified | CC: | rhel-process-autobot, watson-tool-maintainers |
| Target Milestone: | --- | Keywords: | Security |
| Target Release: | --- | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | --- | |
| Doc Text: |
A flaw was found in the Linux kernel's Multi-Generational Least Recently Used (MGLRU) page table walker. When memory cgroup (memcg) reparenting occurs concurrently with page table walks, stale batch updates can lead to an underestimation of the number of pages. This can prevent the kernel from reclaiming memory effectively, potentially causing premature Out Of Memory (OOM) conditions and system instability.
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | Type: | --- | |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
In the Linux kernel, the following vulnerability has been resolved: mm: mglru: fix stale batch updates after memcg reparenting The mglru page table walker batches per-generation size deltas in walk->nr_pages while walking page tables without holding the lruvec lock. The reset_batch_size() later folds those deltas into walk->lruvec under the lruvec lock. The page table walker can run concurrently with the memcg reparenting path as follows: CPU0 CPU1 ==== ==== walk_mm --> walk_page_range --> update_batch_size --> walk->nr_pages += delta mem_cgroup_css_offline --> memcg_reparent_objcgs --> lock lruvec lru_gen_reparent_memcg --> reparent child folios to parent unlock lruvec lock lruvec reset_batch_size --> child lrugen->nr_pages += delta This will trigger the following warning in lru_gen_exit_memcg(): VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0, sizeof(lruvec->lrugen.nr_pages))); And the user-visible impact of underestimated nr_pages in MGLRU was premature OOMs because MGLRU does not try to reclaim memory when nr_pages reaches zero, but there are still more pages. To fix it, make reset_batch_size() check CSS_DYING under RCU before flushing the pending batch. A non-dying memcg keeps the original lruvec stable against RCU-delayed offlining; a dying memcg redirects the deltas to the first non-dying ancestor.