# CVE-2026-90326: blk-cgroup: fix race between policy activation and blkg destruction

> A race condition in the Linux kernel block cgroup subsystem allows use-after-free, potentially enabling local attackers to execute code or escalate privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-102774, BELL-CVE-2026-90326, DEBIAN-CVE-2026-90326, GHSA-qj9w-qwpx-8wfp, UBUNTU-CVE-2026-90326

## What is CVE-2026-90326?

CVE-2026-90326 is a high-severity use after free vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

blk-cgroup: fix race between policy activation and blkg destruction

When switching an IO scheduler on a block device, blkcg_activate_policy()
allocates blkg_policy_data (pd) for all blkgs attached to the queue.
However, blkcg_activate_policy() may race with concurrent blkcg deletion,
leading to use-after-free and memory leak issues.

The use-after-free occurs in the following race:

T1 (blkcg_activate_policy):
  - Successfully allocates pd for blkg1 (loop0->queue, blkcgA)
  - Fails to allocate pd for blkg2 (loop0->queue, blkcgB)
  - Enters the enomem rollback path to release blkg1 resources

T2 (blkcg deletion):
  - blkcgA is deleted concurrently
  - blkg1 is freed via blkg_free_workfn()
  - blkg1->pd is freed

T1 (continued):
  - Rollback path accesses blkg1->pd->online after pd is freed
  - Triggers use-after-free

In addition, blkg_free_workfn() frees pd before removing the blkg from
q->blkg_list. This allows blkcg_activate_policy() to allocate a new pd
for a blkg that is being destroyed, leaving the newly allocated pd
unreachable when the blkg is finally freed.

Fix these races by extending blkcg_mutex coverage to serialize
blkcg_activate_policy() rollback and blkg destruction, ensuring pd
lifecycle is synchronized with blkg list visibility.

## Which versions are affected by CVE-2026-90326?


## How do I fix CVE-2026-90326?

Apply the vendor's patch.

## Is CVE-2026-90326 being exploited?

There is no known exploitation of CVE-2026-90326 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90326 and fix it if it is affected.

What it is: CVE-2026-90326 is a high-severity use after free vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-90326 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-90326/ (Markdown: https://insights.sbomify.com/CVE-2026-90326/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90326
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90326
- OSV: https://osv.dev/vulnerability/CVE-2026-90326

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90326/
Summaries are generated and may contain mistakes; the official description above is the record.