CVE-2026-90099

net/sched: account classifier filter allocations to memcg

View on CVE.org
Published Sep 17, 2026 CVSS n/a EPSS < 1% KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:

net/sched: account classifier filter allocations to memcg

Allocations in the tc classifier *_change() paths (filter objects,
per-CPU counters, and per-filter aux data) use plain GFP_KERNEL without
__GFP_ACCOUNT, allowing unprivileged users to pin kernel memory outside
memcg charging. The shared tcf_exts_init_ex() action array allocation in
cls_api.c was also uncharged; this patch closes it along with the
per-classifier filter-object/percpu/aux allocations that remain
unaccounted.

Add GFP_KERNEL_ACCOUNT to:
- the shared tcf_exts_init_ex() action array (cls_api.c), common to every
filter of every classifier (32 pointers, 256 bytes);
- the filter-object, per-CPU-counter, and per-filter aux allocations in
cls_basic, cls_bpf, cls_cgroup, cls_flow, cls_flower, cls_fw,
cls_matchall, cls_route and cls_u32;
- the u32_init_knode() replace-path knode allocation (cls_u32.c), which
allocates the same struct tc_u_knode + sel.keys on every replace of an
existing knode and was missed by the create-path-only conversion.

Also fix the cls_basic error path: basic_change() inserts fnew into the
IDR before allocating the per-CPU counter. If alloc_percpu() fails the
errout path kfree'd fnew without idr_remove, leaving a dangling pointer
in the IDR. With GFP_KERNEL_ACCOUNT the percpu alloc becomes failable
on demand (memcg at memory.max), making the dead path attacker-reachable
and burning the handle permanently. Add the idr_remove on the percpu
failure path, matching the basic_set_parms failure-path pattern.

Note: vega@nebusec.ai provided a poc for basic_cls, but it was easy to
extend to the other classifiers.

Conditions to recreate the bug:
- CONFIG_NET_SCHED, CONFIG_NET_CLS_* (the classifier being used),
CONFIG_NET_CLS_ACT, CONFIG_MEMCG, CONFIG_USER_NS, CONFIG_NET_NS.
- Unprivileged user in a fresh user+network namespace (unshare -Urn),
or root with CAP_NET_ADMIN.
- Create a large number of tc filters (e.g. tc filter add dev lo
ingress ... <classifier> ...) while watching a memcg-limited cgroup:
system slab grows far faster than memory.current, pinning kernel
memory outside memcg charging.

Remediation

No solution or workaround provided in the CVE record

Tracking

Sign in to view the affected projects.

Advisories

Source ID Title
Debian DLA Debian DLA DLA-4904-1 linux-6.12 security update
Ubuntu USN Ubuntu USN USN-9019-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-9020-1 Linux kernel vulnerabilities
History
Type Values Removed Values Added
Weaknesses CWE-400
Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: net/sched: account classifier filter allocations to memcg Allocations in the tc classifier *_change() paths (filter objects, per-CPU counters, and per-filter aux data) use plain GFP_KERNEL without __GFP_ACCOUNT, allowing unprivileged users to pin kernel memory outside memcg charging. The shared tcf_exts_init_ex() action array allocation in cls_api.c was also uncharged; this patch closes it along with the per-classifier filter-object/percpu/aux allocations that remain unaccounted. Add GFP_KERNEL_ACCOUNT to: - the shared tcf_exts_init_ex() action array (cls_api.c), common to every filter of every classifier (32 pointers, 256 bytes); - the filter-object, per-CPU-counter, and per-filter aux allocations in cls_basic, cls_bpf, cls_cgroup, cls_flow, cls_flower, cls_fw, cls_matchall, cls_route and cls_u32; - the u32_init_knode() replace-path knode allocation (cls_u32.c), which allocates the same struct tc_u_knode + sel.keys on every replace of an existing knode and was missed by the create-path-only conversion. Also fix the cls_basic error path: basic_change() inserts fnew into the IDR before allocating the per-CPU counter. If alloc_percpu() fails the errout path kfree'd fnew without idr_remove, leaving a dangling pointer in the IDR. With GFP_KERNEL_ACCOUNT the percpu alloc becomes failable on demand (memcg at memory.max), making the dead path attacker-reachable and burning the handle permanently. Add the idr_remove on the percpu failure path, matching the basic_set_parms failure-path pattern. Note: vega@nebusec.ai provided a poc for basic_cls, but it was easy to extend to the other classifiers. Conditions to recreate the bug: - CONFIG_NET_SCHED, CONFIG_NET_CLS_* (the classifier being used), CONFIG_NET_CLS_ACT, CONFIG_MEMCG, CONFIG_USER_NS, CONFIG_NET_NS. - Unprivileged user in a fresh user+network namespace (unshare -Urn), or root with CAP_NET_ADMIN. - Create a large number of tc filters (e.g. tc filter add dev lo ingress ... <classifier> ...) while watching a memcg-limited cgroup: system slab grows far faster than memory.current, pinning kernel memory outside memcg charging.
Title net/sched: account classifier filter allocations to memcg
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Oct 30, 2026, 12:34 PM
Reserved
Sep 11, 2026, 7:38 PM

View source JSON

No data.

Status
Received
Published
Sep 17, 2026, 5:17 PM
Modified
Oct 30, 2026, 1:20 PM

View source JSON

No data.

Updated
Sep 20, 2026, 3:30 AM

JSON