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.
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:
n/a
EPSS:
n/a
KEV:
No
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
||||||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No solution or workaround provided in the CVE record.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
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Advisories
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References
History
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 |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-14T13:27:46.003Z
Reserved: 2026-09-25T10:25:14.347Z
Link: CVE-2026-98414
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-14T14:17:52.673
Modified: 2026-10-14T14:17:52.673
Link: CVE-2026-98414
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.