CVE-2026-63804: gfs2: fix use-after-free in gfs2_qd_dealloc

High 7.8 EPSS 0.1% 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.

CVE-2026-63804CVE identifier
7.8CVSS 3.1 base score (high)
0.1%EPSS: chance of exploitation in the next 30 days (higher than 3% of CVEs)
2026-07-19published

What do these terms mean? CVE · CVSS score · exploited (KEV) · EPSS · backported fix · all terms

What to do now

Check whether you run Linux kernel and which version (commands below).
Install the fixed version for your system: see “Patch it” below.
Reboot into the new kernel (uname -r to confirm); live patching (kpatch, Ubuntu Livepatch, SUSE kGraft/klp) can defer the reboot for some CVEs

Affected and fixed versions

Affected:

Linux Linux a475c5dd16e57c570113eccba51955b5df8bb052 to before 4fe388218826df8607ae41a6305df67db08a9093
Linux Linux a475c5dd16e57c570113eccba51955b5df8bb052 to before 8745d9f7e1682c39f0a1578895ac74205e2a6757
Linux Linux a475c5dd16e57c570113eccba51955b5df8bb052 to before b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0
Linux Linux a475c5dd16e57c570113eccba51955b5df8bb052 to before 9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0
Linux Linux a475c5dd16e57c570113eccba51955b5df8bb052 to before f9c9ec2c319f843b70ecdf939d48b52d189bc081
Linux Linux 6.6

Patch it

Use the commands for your system. Distribution packages often keep an older version number with the fix backported, so compare with the fixed package versions in the table below, not only with the upstream version.

Debian

sudo apt update
sudo apt install --only-upgrade linux-image-amd64

Ubuntu

sudo apt update
sudo apt install --only-upgrade linux-image-generic (or the installed flavour: linux-image-aws, -azure, -gcp, -virtual)

RHEL, AlmaLinux, Rocky, Oracle

sudo dnf upgrade --refresh kernel

Fedora

sudo dnf upgrade --refresh kernel

SUSE / openSUSE

sudo zypper refresh
sudo zypper update kernel-default

Amazon Linux

sudo dnf upgrade --releasever=latest kernel kernel6.12

Arch Linux

sudo pacman -Syu

Alpine

apk update && apk upgrade linux-lts linux-virt

FreeBSD

not Linux

General update steps for every system are on the Linux and Unix & BSD pages; after updating, see which services to restart.

Fix status in Linux distributions

Release	Package	Status	Fixed version / advisory
Debian 12	`linux`	not affected
Debian 13	`linux`	fixed	`6.12.95-1`
Debian testing	`linux`	fixed	`7.1.3-1`
Red Hat Enterprise Linux 9	`kernel`	fix deferred
Red Hat Enterprise Linux 8	`kernel`	fix deferred
Red Hat Enterprise Linux 8	`kernel-rt`	fix deferred
Red Hat Enterprise Linux 7	`kernel`	fix deferred
Red Hat Enterprise Linux 7	`kernel-rt`	fix deferred
Red Hat Enterprise Linux 6	`kernel`	out of support scope

From the Debian security tracker, Ubuntu CVE tracker and Red Hat Security Data API, refreshed every few hours.

Sources

Page generated automatically from official sources on 2026-11-03 18:05 UTC. Always confirm with your vendor's advisory.