---
id: CVE-2026-93100
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()

  A struct rdtgroup is reference counted via rdtgroup::waitcount
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()

  A struct rdtgroup is reference counted via rdtgroup::waitcount. Callers that
  need the structure to remain valid…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= b8511ccc75c033f6d54188ea4df7bf1e85778740 <
    ae69f936e8ffed553d899ba4c02f8a7461a89e54
  - >-
    Linux >= b8511ccc75c033f6d54188ea4df7bf1e85778740 <
    4c593c62c1499665baebbb41b70e2c9b7e947b86
  - >-
    Linux >= b8511ccc75c033f6d54188ea4df7bf1e85778740 <
    f5bcf539484d2d604c2f2330e09487ea090b21c7
  - Linux d20edc0bca5577bab38acb5b190619c922ddebf8
  - Linux 1b006f8cbde9f3dabdfafe2ff7aa9f831ed5b625
  - Linux 40300f986e47dbc8f1d02e5080385f5cf9f85f70
  - Linux b5a4949897ebada8132d54c93208989482503103
  - Linux >= 4.14.170 < 4.15
  - Linux >= 4.19.102 < 4.20
  - Linux >= 5.4.18 < 5.5
  - Linux >= 5.5.2 < 5.6
  - Linux 5.6
published: '2026-09-17'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T17:18:04.223'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-93100'
references:
  - url: 'https://git.kernel.org/stable/c/4c593c62c1499665baebbb41b70e2c9b7e947b86'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/ae69f936e8ffed553d899ba4c02f8a7461a89e54'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f5bcf539484d2d604c2f2330e09487ea090b21c7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-17T16:21:47.757Z'
epss: 0.00206
epssPercentile: 0.09502
---

## Overview

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

fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()

A struct rdtgroup is reference counted via rdtgroup::waitcount. Callers that
need the structure to remain valid across a sleep (while waiting on acquiring
rdtgroup_mutex) take a reference with rdtgroup_kn_get() and release it with
rdtgroup_kn_put().

The release path is intended to serve as the fallback freer: if the count
drops to zero and the group has already been marked RDT_DELETED,
rdtgroup_kn_put() frees the structure.

The bulk teardown paths free_all_child_rdtgrp() and rmdir_all_sub() resulting
from a resctrl directory remove or resctrl fs unmount act as the primary
freer: they hold rdtgroup_mutex and free each rdtgroup whose waitcount is
zero, otherwise they set RDT_DELETED and leave the freeing to the last waiter.

These two freers race. rdtgroup_kn_put() commits waitcount == 0 with
atomic_dec_and_test() outside rdtgroup_mutex, then reads rdtgroup::flags.
Between those two operations a concurrent caller of free_all_child_rdtgrp()
or rmdir_all_sub() (which holds the mutex) can observe waitcount == 0 via
atomic_read(), call rdtgroup_remove(), and kfree() the structure.

The subsequent read of rdtgroup::flags in rdtgroup_kn_put() is then
a use-after-free, and the structure may even be freed twice if the freed
memory happens to satisfy the RDT_DELETED flag check.

Replace the bare atomic_dec_and_test() with atomic_dec_and_mutex_lock() so
that the decrement-to-zero takes rdtgroup_mutex before the count becomes
globally visible. The inspection of rdtgroup::flags then runs under the same
mutex held by the bulk freers, making the two paths mutually exclusive.

The common case where the count does not reach zero remains lock-free. Defer
kernfs_unbreak_active_protection() until after the mutex is dropped since
kernfs active protections functionally wrap rdtgroup_mutex. Remove resource
group, which in turn drops its kernfs reference, after kernfs protection is
restored.

  [ bp: Split the commit messsages into smaller, easier-parseable paragraphs. ]

## Remediation

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