---
id: CVE-2026-98022
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: cap tx_queue_len at S16_MAX to prevent oversized ring allocations

  Several subsystems allocate ring buffers sized by dev->tx_queue_len
  with no upper bound
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: cap tx_queue_len at S16_MAX to prevent oversized ring allocations

  Several subsystems allocate ring buffers sized by dev->tx_queue_len
  with no upper bound. An unpr…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 6a643ddb5624be7e0694d49f5765a8d41c1ab6d0 <
    81c0e02076989743a603806a5a4f44d2c40dc01f
  - >-
    Linux >= 6a643ddb5624be7e0694d49f5765a8d41c1ab6d0 <
    081340cf70a789b94b4174af54a63ffd49677a4e
  - >-
    Linux >= 6a643ddb5624be7e0694d49f5765a8d41c1ab6d0 <
    a03b927bae4af5c23fd5315a237855c17cc8f422
  - >-
    Linux >= 6a643ddb5624be7e0694d49f5765a8d41c1ab6d0 <
    66ab4c59b74db7ab53a1c9083feaaede393a96a0
  - Linux 4.16
published: '2026-09-25'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T11:17:30.740'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-98022'
references:
  - url: 'https://git.kernel.org/stable/c/081340cf70a789b94b4174af54a63ffd49677a4e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/66ab4c59b74db7ab53a1c9083feaaede393a96a0'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/81c0e02076989743a603806a5a4f44d2c40dc01f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a03b927bae4af5c23fd5315a237855c17cc8f422'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-25T11:06:38.855Z'
---

## Overview

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

net: cap tx_queue_len at S16_MAX to prevent oversized ring allocations

Several subsystems allocate ring buffers sized by dev->tx_queue_len
with no upper bound. An unprivileged user (via unshare -Urn) can set a
huge tx_queue_len and exhaust global memory with ring allocations:

- pfifo_fast: pfifo_fast_init() and pfifo_fast_change_tx_queue_len()
  allocate 3 skb_array rings of tx_queue_len entries each.
- tun: tun_queue_resize() and the queue-attach path resize ptr_rings
  to tx_queue_len on the NETDEV_CHANGE_TX_QUEUE_LEN notifier.
- tap (macvtap/ipvtap): tap_queue_resize() and tap_init() resize/init
  ptr_rings to tx_queue_len on the same notifier.

netif_change_tx_queue_len() is the single entry point for IFLA_TXQLEN,
sysfs, and the SIOCSIFTXQLEN ioctl. Cap new_len at S16_MAX (32767)
there so the oversized value is rejected at set time. This takes
effect whether the device is up or down, before dev->tx_queue_len is
written, before any notifier fires, and before any ring is allocated.
The "> S16_MAX" check also subsumes the previous unsigned-long
truncation test, and a negative ifr_qlen from the ioctl lands far
above the cap after conversion, so both old failure modes are covered
by the one comparison.

tx_queue_len is ambigious: both a per-ring sizing multiplier and a
default queue-length/limit knob for consumers that allocate
nothing at set time (pfifo/bfifo/gred/plug/sfb limits, htb
direct_qlen, qfq max_classes, teql). 32767 is chosen as the largest
value NLA_POLICY_FULL_RANGE can express for the u32 IFLA_TXQLEN
policy in patch 2/3 while staying a legitimate queue length on
high-BDP paths; the ring-memory trade-off of a shared knob is
disclosed below.

Conditions to recreate the bug:
- CONFIG_NET_SCHED=y, CONFIG_VETH=y, CONFIG_USER_NS=y, CONFIG_NET_NS=y.
- Unprivileged user in a fresh user+net namespace (unshare -Urn).
- pfifo_fast: create veth pairs, set tx_queue_len to 500000, attach
  mq+pfifo_fast. ~28 iterations OOMs a 2GB guest.
- tun: create 50 tun devices with IFF_MULTI_QUEUE, set tx_queue_len to
  500000, open 8 queues each. ~1.6GB of ptr_ring allocations OOMs a
  512MB guest.
- tap: same as tun with IFF_TAP. ~960MB OOMs a 512MB guest.
- On the fixed kernel the oversized tx_queue_len is rejected with
  -ERANGE at set time (all four paths: RTM_SETLINK, RTM_NEWLINK
  create, sysfs, ioctl - the latter two via this check, the former
  two via this check and the 2/3 parse policy respectively).

## Remediation

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