---
id: CVE-2026-98104
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted

  gen_new_kid() falls back to returning max (htid | 0xFFF) when both
  idr_alloc_u32() ranges are f…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted

  gen_new_kid() falls back to returning max (htid | 0xFFF) when both
  idr_alloc_u32() ranges are f…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b <
    6890e28840bae4f6805e8de981c4ec8e12a4e064
  - >-
    Linux >= 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b <
    feab9261b537df4ebb8350e4779bc185373059fd
  - >-
    Linux >= 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b <
    f594f04268d01c5fdc975f3f51fc219ea2159ac6
  - >-
    Linux >= 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b <
    d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f
  - Linux 3.16
published: '2026-09-25'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T11:17:40.793'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-98104'
references:
  - url: 'https://git.kernel.org/stable/c/6890e28840bae4f6805e8de981c4ec8e12a4e064'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f594f04268d01c5fdc975f3f51fc219ea2159ac6'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/feab9261b537df4ebb8350e4779bc185373059fd'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-25T11:06:38.826Z'
epss: 0.002
epssPercentile: 0.08839
---

## Overview

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

net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted

gen_new_kid() falls back to returning max (htid | 0xFFF) when both
idr_alloc_u32() ranges are full, instead of reporting an error.
u32_change() trusts that value and inserts a new knode with a handle
that is already live in the hash table, breaking handle uniqueness
within the table's node ID space.

The handle was never reserved in ht->handle_idr, so every later error
path that does idr_remove(&ht->handle_idr, handle) removes the
reservation of a different, live knode, which is then reused — one
failed add compounds into further duplicates.

The 4095 limit is per (table, bucket) — ht->handle_idr is per hash
table and the range is derived from htid (bucketid), so a table with
divisor 256 can legitimately hold 256*4095 knodes.

The sibling helper gen_new_htid() has the same silent in-band failure:
it returns 0 when the tp_c handle pool (1..0x7FF) is full, and
u32_init() publishes the root hash table with handle 0 without
checking.  Two root tables with handle 0 alias in u32_lookup_ht(),
allowing cross-tcf_proto knode add/lookup/delete.  Add the same
exhaustion check that the divisor path already has.

Return an error so u32_change() fails with ENOSPC/ENOMEM when the
node ID space is exhausted, and so u32_init() fails with -ENOMEM
when the hash table ID space is exhausted.  The extack message
distinguishes pool exhaustion (-ENOSPC) from a transient allocation
failure (-ENOMEM).

Conditions to recreate the bug:
- CONFIG_NET_SCHED=y, CONFIG_CLS_U32=y (or =m with module loaded)
- Create a clsact qdisc on a device, then add 4095 u32 filters with
  auto-generated handles to fill the node ID space for the root hash
  table (single bucket). The 4096th auto-handle filter add triggers
  the duplicate handle (fh 800::fff reused). Reachable at Level 2
  (unshare -Urn, namespace-local CAP_NET_ADMIN).
- For gen_new_htid: create 2047 u32 proto entries on the same block
  to fill the tp_c handle pool, then create one more. The root table
  gets handle 0 and aliases with other handle-0 root tables.

## Remediation

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