---
id: CVE-2026-68138
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: serialize qdisc_rtab_list against concurrent get/put

  qdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly
  linked list qdisc_rtab_list and …
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: serialize qdisc_rtab_list against concurrent get/put

  qdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly
  linked list qdisc_rtab_list and …
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
published: '2026-08-10'
updated: '2026-08-23'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-68138'
references:
  - url: 'https://git.kernel.org/stable/c/1b050d09dd1a0ddae83bf012cf4956b7a960235f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4131dd0b6f67acddd616ed7c244e1d3eedd46e7b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6e0241f6cbb149d926ee8efee2c734fea71452cf'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8ddc2eb0d2da9c83f54f1e5720525b461b8480c4'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d981098b76756ed71666a27518eeb69883657c43'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f43ee0c0730d6191629b5ee1ceae27b1ebfdc047'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f93c89392bd3b180b5b7abc6fdae8e3dd667a313'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/fb29e1b41052488ee3f2d115d4a870497ebd7f7d'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68138.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-68138'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2513343'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-68138'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-68138'
  - url: >-
      https://lore.kernel.org/linux-cve-announce/2026081059-CVE-2026-68138-ffa7@gregkh/T
tags:
  - nvd
  - exploit-available
  - csaf
  - vex
  - red-hat
epss: 0.00171
epssPercentile: 0.05686
ingestedAt: '2026-08-23T13:48:06.241Z'
exploits:
  github: 3
  githubRepos:
    - 'https://github.com/aramosf/CVE-2026-68138'
    - 'https://github.com/suominen/CVE-2026-68138'
    - 'https://github.com/jangkrikkbozz/CVE-2026-68138'
  checkedAt: '2026-09-25T08:21:08.583Z'
exploitAvailable: true
vendor: Red Hat
product: Red Hat Enterprise Linux 9
affected:
  - enterprise_linux 10
  - enterprise_linux 8
  - enterprise_linux 9
  - enterprise_linux_for_nvidia 26
cwe:
  - CWE-364
---

## Overview

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

net/sched: serialize qdisc_rtab_list against concurrent get/put

qdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly
linked list qdisc_rtab_list and a plain non-atomic 'int refcnt' with no
lock. This was only safe because every caller historically held the RTNL
mutex, which serialized all rate-table lookups, inserts and frees.

That invariant no longer holds. cls_flower sets
TCF_PROTO_OPS_DOIT_UNLOCKED, so tc_new_tfilter() keeps rtnl_held == false
for it and sets TCA_ACT_FLAGS_NO_RTNL. That flag propagates through
tcf_exts_validate_ex() -> tcf_action_init() -> tcf_action_init_1() ->
tcf_police_init(), which calls qdisc_get_rtab()/qdisc_put_rtab() with the
RTNL mutex NOT held. Two RTM_NEWTFILTER requests on different CPUs, each
adding a flower filter with a police action carrying the same rate, then
race on qdisc_rtab_list and on the non-atomic refcnt, leading to a
use-after-free / double-free of the kmalloc-2k struct qdisc_rate_table.
qdisc_rtab_list is a single global (not per-netns), so the corrupted
object is shared system-wide.

  BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160
   qdisc_put_rtab+0x12f/0x160
   tcf_police_init+0xda9/0x1590
   tcf_action_init_1+0x460/0x6b0
   tcf_action_init+0x439/0xa40
   tcf_exts_validate_ex+0x42d/0x550
   fl_change+0xddd/0x7da0
   tc_new_tfilter+0xaa7/0x2420
   rtnetlink_rcv_msg+0x95e/0xe90
  which belongs to the cache kmalloc-2k of size 2048

Protect qdisc_rtab_list and the refcount with a dedicated spinlock. The
(sleeping, GFP_KERNEL) allocation in qdisc_get_rtab() is performed before
taking the lock; if a concurrent inserter added an identical table in the
meantime the freshly allocated one is freed under the lock, so no
duplicate is leaked. qdisc_put_rtab() now decrements the refcount and
unlinks under the same lock.

## Remediation

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

## Vendor advisories

- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat Enterprise Linux for NVIDIA 26 · no fix planned: Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat Enterprise Linux for NVIDIA 26 · updated 2026-09-22 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68138.json)