---
id: CVE-2026-63804
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  gfs2: fix use-after-free in gfs2_qd_dealloc

  gfs2_qd_dealloc(), called as an RCU callback from gfs2_qd_dispose(),
  accesses the superblock object sdp through qd->qd_sbd …
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  gfs2: fix use-after-free in gfs2_qd_dealloc

  gfs2_qd_dealloc(), called as an RCU callback from gfs2_qd_dispose(),
  accesses the superblock object sdp through qd->qd_sbd …
severity: none
published: '2026-07-19'
updated: '2026-07-19'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63804'
references:
  - url: 'https://git.kernel.org/stable/c/4fe388218826df8607ae41a6305df67db08a9093'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8745d9f7e1682c39f0a1578895ac74205e2a6757'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f9c9ec2c319f843b70ecdf939d48b52d189bc081'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
ingestedAt: '2026-07-20T09:37:17.517Z'
epss: 0.00132
epssPercentile: 0.03144
---

## Overview

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

gfs2: fix use-after-free in gfs2_qd_dealloc

gfs2_qd_dealloc(), called as an RCU callback from gfs2_qd_dispose(),
accesses the superblock object sdp through qd->qd_sbd after freeing qd.
It does so to decrement sd_quota_count and wake up sd_kill_wait.

However, by the time the RCU callback runs, gfs2_put_super() may have
already freed sdp via free_sbd().  This can happen when
gfs2_quota_cleanup() is called during unmount: it disposes of quota
objects via call_rcu() and then waits on sd_kill_wait with a 60-second
timeout.  If the timeout expires, or if gfs2_gl_hash_clear() triggers
additional qd_put() calls that schedule more RCU callbacks after the
wait completes, gfs2_put_super() will proceed to free the superblock
while RCU callbacks referencing it are still pending.

Add an rcu_barrier() before free_sbd() in gfs2_put_super() to ensure
all pending RCU callbacks (including gfs2_qd_dealloc) have completed
before the superblock is freed.

## Remediation

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