gfs2: fix use-after-free in gfs2_qd_dealloc

Answer in brief

CVE-2026-63804 records a High severity (CVSS 7.8) vulnerability in gfs2: fix use-after-free in gfs2_qd_dealloc. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Jul 19, 2026Updated Aug 17, 2026Source checked Oct 1, 2026First seen by HOL Aug 17, 2026Material review Aug 17, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.8
Exploitation: Not marked as known exploited
Affected software: 3 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
Product	Affected versions	Fixed versions
cpe:2.3:o:linux:linux_kernel::::::::	Not reported	Not reported

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=a475c5dd16e57c570113eccba51955b5df8bb052 <4fe388218826df8607ae41a6305df67db08a9093 \|\| >=a475c5dd16e57c570113eccba51955b5df8bb052 <8745d9f7e1682c39f0a1578895ac74205e2a6757 \|\| >=a475c5dd16e57c570113eccba51955b5df8bb052 <b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0 \|\| >=a475c5dd16e57c570113eccba51955b5df8bb052 <9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0 \|\| >=a475c5dd16e57c570113eccba51955b5df8bb052 <f9c9ec2c319f843b70ecdf939d48b52d189bc081	4fe388218826df8607ae41a6305df67db08a9093, 8745d9f7e1682c39f0a1578895ac74205e2a6757, b85ef03f726b15047a6fa6d11b639bdf6c0ee4f0, 9d0d5ba20cad661f7f287d4c66d2c19022ce2fd0, f9c9ec2c319f843b70ecdf939d48b52d189bc081
Linux/Linuxgeneric	6.6	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to 4fe388218826df8607ae41a6305df67db08a9093 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Jul 19, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 17, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 17, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.