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Vulnerability record · CVE-2026-63804 · published 19 July 2026

CVE-2026-63804: Linux kernel use after free vulnerability

Linux · Linux Kernel

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.

7.8 CVSS 3.1 High EPSS 0.13% · top 97.7% CWE-416 · Use after free
7.8CVSS 3.1 base score
0.13%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
5References
17 Aug 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://git.kernel.org/stable/c/4fe388218826df8607ae41a6305df67db08a9093 Patch
https://git.kernel.org/stable/c/8745d9f7e1682c39f0a1578895ac74205e2a6757 Patch
https://git.kernel.org/stable/c/9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0 Patch
https://git.kernel.org/stable/c/b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0 Patch
https://git.kernel.org/stable/c/f9c9ec2c319f843b70ecdf939d48b52d189bc081 Patch

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Source: NIST National Vulnerability Database (record CVE-2026-63804), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.