# CVE-2026-97416: btrfs: balance: fix potential bg lookup failure in btrfs_may_alloc_data_chunk()

> A local attacker with low privileges can cause a kernel crash via null pointer dereference in btrfs balance operations when handling corrupted filesystem metadata.

- **Severity:** Not scored
- **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:** 24 Sep 2026
- **Updated:** 3 Oct 2026
- **Also known as:** AZL-103586, BELL-CVE-2026-97416, DEBIAN-CVE-2026-97416, GHSA-2886-j9mj-2v9x, UBUNTU-CVE-2026-97416

## What is CVE-2026-97416?

CVE-2026-97416 is a vulnerability in Linux, published on 24 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:

btrfs: balance: fix potential bg lookup failure in btrfs_may_alloc_data_chunk()

[BUG]
Running btrfs balance can trigger a null-ptr-deref before relocating a
data chunk when metadata corruption leaves a chunk in the chunk tree
without a corresponding block group in the in-memory cache:

  KASAN: null-ptr-deref in range [0x0000000000000088-0x000000000000008f]
  RIP: 0010:btrfs_may_alloc_data_chunk+0x40/0x1c0 fs/btrfs/volumes.c:3601
  Call Trace:
    __btrfs_balance fs/btrfs/volumes.c:4217 [inline]
    btrfs_balance+0x2516/0x42b0 fs/btrfs/volumes.c:4604
    btrfs_ioctl_balance fs/btrfs/ioctl.c:3577 [inline]
    btrfs_ioctl+0x25cf/0x5b90 fs/btrfs/ioctl.c:5313
    ...

[CAUSE]
__btrfs_balance() iterates the on-disk chunk tree and passes the chunk
logical bytenr to btrfs_may_alloc_data_chunk() before relocating a data
chunk. That helper then queries the in-memory block group cache:

  cache = btrfs_lookup_block_group(fs_info, chunk_offset);
  chunk_type = cache->flags;   /* cache may be NULL */

A corrupt image can contain a chunk item whose matching block group
item is missing, so no block group is ever inserted into the cache. In
that case btrfs_lookup_block_group() returns NULL.

The code only guards this with ASSERT(cache), which becomes a no-op when
CONFIG_BTRFS_ASSERT is disabled. The subsequent dereference of
cache->flags therefore crashes the kernel.

[FIX]
Add a NULL check after btrfs_lookup_block_group() in
btrfs_may_alloc_data_chunk() and print and error message for clarity.

## Which versions are affected by CVE-2026-97416?


## How do I fix CVE-2026-97416?

Apply the vendor's patch.

## Is CVE-2026-97416 being exploited?

There is no known exploitation of CVE-2026-97416 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97416 and fix it if it is affected.

What it is: CVE-2026-97416 is a vulnerability in Linux, published on 24 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-2026-97416 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-2026-97416/ (Markdown: https://insights.sbomify.com/CVE-2026-97416/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97416
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97416
- OSV: https://osv.dev/vulnerability/CVE-2026-97416

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97416/
Summaries are generated and may contain mistakes; the official description above is the record.