---
id: CVE-2026-90058
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup

  qdisc_get_stab() accepts a user-supplied size table, and
  __qdisc_calculate_pkt_len() amplifies qdisc_pkt_le…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup

  qdisc_get_stab() accepts a user-supplied size table, and
  __qdisc_calculate_pkt_len() amplifies qdisc_pkt_le…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    4f0f4b09a95ef602fbdae948326beadd9c20eab3
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    0bc5a6280a132a2170c6fa742436e01b635f02de
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    448c34421b38ec7c93a0060a885218ca319d382b
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    82fdbf49b9f7528c82bf608cfa9710e5f81a198c
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    6e78792d8ce1fa3561713860ee8086901dde4f99
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    1a5c26e586481bc82abc19ac92c3d9f10518f525
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    16d21a27df3f50b7251c9388fc5a7ab22703b469
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    8f735d64382dcf162f4276d6699d03ad2f859c0b
  - Linux 2.6.12
published: '2026-09-17'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T17:16:54.440'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-90058'
references:
  - url: 'https://git.kernel.org/stable/c/0bc5a6280a132a2170c6fa742436e01b635f02de'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/16d21a27df3f50b7251c9388fc5a7ab22703b469'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/1a5c26e586481bc82abc19ac92c3d9f10518f525'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/448c34421b38ec7c93a0060a885218ca319d382b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4f0f4b09a95ef602fbdae948326beadd9c20eab3'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6e78792d8ce1fa3561713860ee8086901dde4f99'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/82fdbf49b9f7528c82bf608cfa9710e5f81a198c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8f735d64382dcf162f4276d6699d03ad2f859c0b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-17T16:21:47.902Z'
epss: 0.0022
epssPercentile: 0.11068
---

## Overview

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

net/sched: bound qdisc_pkt_len to prevent qdisc soft lockup

qdisc_get_stab() accepts a user-supplied size table, and
__qdisc_calculate_pkt_len() amplifies qdisc_pkt_len() through the
overhead, the size-table data (u16), and size_log (up to
STAB_SIZE_LOG_MAX). A crafted stab can therefore set qdisc_pkt_len()
to ~1 GiB for an ordinary skb. Per-flow deficit schedulers such as
DRR and ETS replenish one quantum per loop iteration; with a tiny
quantum (1) they spin billions of times under the qdisc lock,
producing a soft lockup / RCU stall as illustrated by vega@nebusec.ai.

Cap the final qdisc_pkt_len() to QDISC_PKT_LEN_MAX so the size-table
amplification cannot drive deficit schedulers into an unbounded loop.
A legitimate size table (e.g. qfq's overhead 999999999, which is
handled by dropping) is still accepted.

Introduce cap QDISC_PKT_LEN_MAX (1 << 20) = 1 MiB which is well above
any legitimate single-skb wire length: the largest current skb->len
is GSO_MAX_SIZE (524280), and an ATM-style size table (53/48 cell tax)
amplifies that to ~578 KB, both comfortably below 1 MiB. At the same
time, 1 MiB bounds the deficit refill loop to ~1M iterations per
packet with quantum=1, which completes in a few milliseconds well
under the demonstrated softlockup threshold (~10^9 iterations).

Conditions to recreate the bug:
- CONFIG_NET_SCHED=y, CONFIG_NET_SCH_DRR=y (or CONFIG_NET_SCH_ETS=y).
- Attach a DRR (or ETS) root qdisc with a crafted TCA_STAB that
  amplifies qdisc_pkt_len to ~1 GiB (e.g. size_log=15, data=[32768]).
- Add a class with a tiny quantum of 1 and send one small packet; the
  deficit loop spins billions of times under the qdisc lock and trips
  the softlockup detector (panic with kernel.softlockup_panic=1).
- Reachable as root or from an unprivileged user in a fresh user+net
  namespace (unshare -Urn) with namespace-local CAP_NET_ADMIN.

## Remediation

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