# CVE-2022-49834: nilfs2: fix use-after-free bug of ns_writer on remount

> A use-after-free vulnerability in the Linux kernel nilfs2 filesystem allows attackers to execute arbitrary code or escalate privileges via remount operations.

- **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:** 1 May 2025
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2022-49834, GHSA-7jwj-6g7w-4c9q, UBUNTU-CVE-2022-49834

## What is CVE-2022-49834?

CVE-2022-49834 is a high-severity use after free vulnerability in Linux kernel, published on 1 May 2025. 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:

nilfs2: fix use-after-free bug of ns_writer on remount

If a nilfs2 filesystem is downgraded to read-only due to metadata
corruption on disk and is remounted read/write, or if emergency read-only
remount is performed, detaching a log writer and synchronizing the
filesystem can be done at the same time.

In these cases, use-after-free of the log writer (hereinafter
nilfs->ns_writer) can happen as shown in the scenario below:

 Task1                               Task2
 --------------------------------    ------------------------------
 nilfs_construct_segment
   nilfs_segctor_sync
     init_wait
     init_waitqueue_entry
     add_wait_queue
     schedule
                                     nilfs_remount (R/W remount case)
				       nilfs_attach_log_writer
                                         nilfs_detach_log_writer
                                           nilfs_segctor_destroy
                                             kfree
     finish_wait
       _raw_spin_lock_irqsave
         __raw_spin_lock_irqsave
           do_raw_spin_lock
             debug_spin_lock_before  <-- use-after-free

While Task1 is sleeping, nilfs->ns_writer is freed by Task2.  After Task1
waked up, Task1 accesses nilfs->ns_writer which is already freed.  This
scenario diagram is based on the Shigeru Yoshida's post [1].

This patch fixes the issue by not detaching nilfs->ns_writer on remount so
that this UAF race doesn't happen.  Along with this change, this patch
also inserts a few necessary read-only checks with superblock instance
where only the ns_writer pointer was used to check if the filesystem is
read-only.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2022-49834?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2022-49834?

Apply the vendor's patch.

## Is CVE-2022-49834 being exploited?

There is no known exploitation of CVE-2022-49834 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2022-49834 and fix it if it is affected.

What it is: CVE-2022-49834 is a high-severity use after free vulnerability in Linux kernel, published on 1 May 2025. 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-2022-49834 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2022-49834/ (Markdown: https://insights.sbomify.com/CVE-2022-49834/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2022-49834
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2022-49834
- OSV: https://osv.dev/vulnerability/CVE-2022-49834

---
From sbomify Insights: https://insights.sbomify.com/CVE-2022-49834/
Summaries are generated and may contain mistakes; the official description above is the record.