---
id: CVE-2026-90099
title: |-
  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)…
summary: |-
  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)…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 0da974f4f303a6842516b764507e3c0a03f41e5a <
    18c68c8f3d3ff0a4def1391021b439c4333a6c71
  - >-
    Linux >= 0da974f4f303a6842516b764507e3c0a03f41e5a <
    1beb81947eb486716af80db7a584f9e9fef7e003
  - Linux 2.6.18
published: '2026-09-17'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T17:17:01.567'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-90099'
references:
  - url: 'https://git.kernel.org/stable/c/18c68c8f3d3ff0a4def1391021b439c4333a6c71'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/1beb81947eb486716af80db7a584f9e9fef7e003'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-17T16:21:47.890Z'
epss: 0.00198
epssPercentile: 0.08447
---

## Overview

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

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.