Description
In the Linux kernel, the following vulnerability has been resolved:

memcg: avoid charging the root memcg from obj_cgroup_charge_pages()

obj_cgroup_charge_pages() resolves the objcg to its memcg and calls
try_charge_memcg(), which does not short circuit the root memcg. That
memcg can be the root memcg: obj_cgroup_is_root() reflects the memcg the
objcg was created for and is never updated, while memcg_reparent_objcgs()
does redirect objcg->memcg to the parent on rmdir. An objcg of a dying
child of root therefore passes every obj_cgroup_is_root() filter but
resolves to the root memcg.

Folios keep the objcg they were charged with, so this is easy to reach
through zswap: allocate anon memory in a cgroup, move the task out, remove
the cgroup, then write to the root cgroup's memory.reclaim. The reclaimed
folios are charged through the reparented objcg and end up in
refill_stock() with the root memcg:

WARNING: mm/memcontrol.c:2198 at refill_stock+0x644/0x940
refill_stock+0x644/0x940
try_charge_memcg+0x12d6/0x1570
__obj_cgroup_charge+0x35/0xf0
obj_cgroup_charge+0x1de/0x210
obj_cgroup_charge_zswap+0x83/0x270
zswap_store+0x1620/0x2000
swap_writeout+0x94c/0x14c0
shrink_folio_list+0x3388/0x52b0
[...]
try_to_free_mem_cgroup_pages+0x30d/0x830
user_proactive_reclaim+0x504/0x840
memory_reclaim+0x1f/0x30

Beyond the warning, the charge is asymmetric: obj_cgroup_uncharge_pages()
skips refill_stock() for the root memcg, so the root's page counter grows
and is never uncharged. It is not user visible, since memory.current is
not exposed on the root, but it is a leak.

Use try_charge(), which returns early for the root memcg, restoring the
symmetry with obj_cgroup_uncharge_pages().

The above sequence was scripted into a standalone reproducer (zswap on,
swap on a virtio disk, 512MB of anon memory faulted in inside a child of
the root cgroup, the task then migrated to the root cgroup, the child
removed, followed by "echo 600M swappiness=max > memory.reclaim" on the
root) and run in a CONFIG_DEBUG_VM=y VM. It reproduces the splat on the
first zswap store of a reparented folio, with the same call chain as the
report. With this patch applied the splat is gone while the zswap store
count over the run is unchanged, so the same path is still exercised.
cgroup selftests test_zswap, test_kmem and test_memcontrol show no new
failures.
Published: 2026-10-14
Score: 2.3 Low
EPSS: < 1% Very Low
KEV: No
Impact: Denial of Service
Action: Apply Patch
AI Analysis

Impact

The vulnerability arises from an asymmetric memory accounting bug in the Linux kernel’s memcg subsystem when zswap is used. During a memory reclamation cycle, pages belonging to an object cgroup that has been removed and reparented to the root memory cgroup are incorrectly charged to the root memcg. Because the uncharging routine skips the root, its page counter grows indefinitely, producing a memory leak that can ultimately exhaust system memory and cause instability. The bug is not directly user‑visible but can lead to denial of service by draining available memory through repeated zswap usage.

Affected Systems

This flaw affects the Linux kernel in general, with no specific version range provided in the advisory. It was identified and corrected in the source tree, so any kernel build to the patched commit contains the issue.

Risk and Exploitability

The CVSS score of 2.3 indicates low severity, and the EPSS score remains less than 1%. The vulnerability is not listed in the CISA KEV catalog. Exploitation would still require local or higher privileges to manipulate cgroup hierarchies and trigger zswap. The risk remains low but could lead to memory exhaustion and a denial of service if the sequence described in the reproduction steps is repeatedly performed.

Generated by OpenCVE AI on October 16, 2026 at 22:46 UTC.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Upgrade the Linux kernel to a version that includes the memcg patch preventing charging of the root memcg.
  • If upgrading immediately is not possible, consider disabling zswap or reducing the "memory.reclaim" setting for the root cgroup to avoid triggering the leaked charging path.
  • Monitor memory usage of the root cgroup, watching for abnormal growth in page counters or memory metrics, and intervene if memory pressure increases unexpectedly.

Generated by OpenCVE AI on October 16, 2026 at 22:46 UTC.

Tracking

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Advisories

No advisories yet.

History

Fri, 16 Oct 2026 12:30:00 +0000

Type Values Removed Values Added
Weaknesses CWE-617
References
Metrics threat_severity

None

 cvssV3_1

{'score': 2.3, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L'}

threat_severity

Low

Thu, 15 Oct 2026 23:00:00 +0000

Type Values Removed Values Added
Weaknesses CWE-401

Thu, 15 Oct 2026 03:45:00 +0000

Type Values Removed Values Added
Weaknesses CWE-401

Wed, 14 Oct 2026 13:45:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: memcg: avoid charging the root memcg from obj_cgroup_charge_pages() obj_cgroup_charge_pages() resolves the objcg to its memcg and calls try_charge_memcg(), which does not short circuit the root memcg. That memcg can be the root memcg: obj_cgroup_is_root() reflects the memcg the objcg was created for and is never updated, while memcg_reparent_objcgs() does redirect objcg->memcg to the parent on rmdir. An objcg of a dying child of root therefore passes every obj_cgroup_is_root() filter but resolves to the root memcg. Folios keep the objcg they were charged with, so this is easy to reach through zswap: allocate anon memory in a cgroup, move the task out, remove the cgroup, then write to the root cgroup's memory.reclaim. The reclaimed folios are charged through the reparented objcg and end up in refill_stock() with the root memcg: WARNING: mm/memcontrol.c:2198 at refill_stock+0x644/0x940 refill_stock+0x644/0x940 try_charge_memcg+0x12d6/0x1570 __obj_cgroup_charge+0x35/0xf0 obj_cgroup_charge+0x1de/0x210 obj_cgroup_charge_zswap+0x83/0x270 zswap_store+0x1620/0x2000 swap_writeout+0x94c/0x14c0 shrink_folio_list+0x3388/0x52b0 [...] try_to_free_mem_cgroup_pages+0x30d/0x830 user_proactive_reclaim+0x504/0x840 memory_reclaim+0x1f/0x30 Beyond the warning, the charge is asymmetric: obj_cgroup_uncharge_pages() skips refill_stock() for the root memcg, so the root's page counter grows and is never uncharged. It is not user visible, since memory.current is not exposed on the root, but it is a leak. Use try_charge(), which returns early for the root memcg, restoring the symmetry with obj_cgroup_uncharge_pages(). The above sequence was scripted into a standalone reproducer (zswap on, swap on a virtio disk, 512MB of anon memory faulted in inside a child of the root cgroup, the task then migrated to the root cgroup, the child removed, followed by "echo 600M swappiness=max > memory.reclaim" on the root) and run in a CONFIG_DEBUG_VM=y VM. It reproduces the splat on the first zswap store of a reparented folio, with the same call chain as the report. With this patch applied the splat is gone while the zswap store count over the run is unchanged, so the same path is still exercised. cgroup selftests test_zswap, test_kmem and test_memcontrol show no new failures.
Title memcg: avoid charging the root memcg from obj_cgroup_charge_pages()
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-10-19T09:19:08.193Z

Reserved: 2026-09-25T10:25:14.347Z

Link: CVE-2026-98414

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-14T14:17:52.673

Modified: 2026-10-19T10:18:46.707

Link: CVE-2026-98414

cve-icon Redhat

Severity : Low

Publid Date: 2026-10-14T00:00:00Z

Links: CVE-2026-98414 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-19T19:45:02Z

Weaknesses