# CVE-2026-74321: btrfs: fix invalid pointer dereference in __btrfs_run_delayed_refs()

> A local attacker can cause a kernel crash by triggering an invalid pointer dereference in the btrfs filesystem delayed reference handling.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-74321, DEBIAN-CVE-2026-74321, GHSA-frrx-chj7-rchf, UBUNTU-CVE-2026-74321

## What is CVE-2026-74321?

CVE-2026-74321 is a high-severity vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

btrfs: fix invalid pointer dereference in __btrfs_run_delayed_refs()

In the beginning of the loop, we try to obtain a locked delayed ref head,
if 'locked_ref' is currently NULL, by calling btrfs_select_ref_head(),
which can return an error pointer. If the error pointer is -EAGAIN we do
a continue and go back to the beginning of the loop, which will not try
again to call btrfs_select_ref_head() since 'locked_ref' is no longer
NULL but it's ERR_PTR(-EAGAIN), and then we do:

   spin_lock(&locked_ref->lock);

against a ERR_PTR(-EAGAIN) value, generating an invalid pointer
dereference.

Fix this by ensuring that 'locked_ref' is set to NULL when
btrfs_select_ref_head() returns ERR_PTR(-EAGAIN) and incrementing 'count'
as well, to prevent infinite looping. We do this by doing a goto to the
bottom of the loop that already sets 'locked_ref' to NULL and does a
cond_resched(), with an increment to 'count' right before the goto.
These measures were in place before the refactoring in commit 0110a4c43451
("btrfs: refactor __btrfs_run_delayed_refs loop") but were unintentionally
lost afterwards.

## Which versions are affected by CVE-2026-74321?


## How do I fix CVE-2026-74321?

Apply the vendor's patch.

## Is CVE-2026-74321 being exploited?

There is no known exploitation of CVE-2026-74321 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74321 and fix it if it is affected.

What it is: CVE-2026-74321 is a high-severity vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74321 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-2026-74321/ (Markdown: https://insights.sbomify.com/CVE-2026-74321/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74321
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74321
- OSV: https://osv.dev/vulnerability/CVE-2026-74321

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74321/
Summaries are generated and may contain mistakes; the official description above is the record.