# CVE-2021-46982: f2fs: compress: fix race condition of overwrite vs truncate

> A race condition in the Linux kernel's f2fs compressed file handling allows a local attacker to trigger a kernel panic, causing denial of service.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/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:** 28 Feb 2024
- **Updated:** 11 May 2026
- **Also known as:** DEBIAN-CVE-2021-46982, GHSA-phj2-fhf8-vr32, UBUNTU-CVE-2021-46982

## What is CVE-2021-46982?

CVE-2021-46982 is a medium-severity vulnerability in Linux kernel, published on 28 Feb 2024. 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:

f2fs: compress: fix race condition of overwrite vs truncate

pos_fsstress testcase complains a panic as belew:

------------[ cut here ]------------
kernel BUG at fs/f2fs/compress.c:1082!
invalid opcode: 0000 [#1] SMP PTI
CPU: 4 PID: 2753477 Comm: kworker/u16:2 Tainted: G           OE     5.12.0-rc1-custom #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
Workqueue: writeback wb_workfn (flush-252:16)
RIP: 0010:prepare_compress_overwrite+0x4c0/0x760 [f2fs]
Call Trace:
 f2fs_prepare_compress_overwrite+0x5f/0x80 [f2fs]
 f2fs_write_cache_pages+0x468/0x8a0 [f2fs]
 f2fs_write_data_pages+0x2a4/0x2f0 [f2fs]
 do_writepages+0x38/0xc0
 __writeback_single_inode+0x44/0x2a0
 writeback_sb_inodes+0x223/0x4d0
 __writeback_inodes_wb+0x56/0xf0
 wb_writeback+0x1dd/0x290
 wb_workfn+0x309/0x500
 process_one_work+0x220/0x3c0
 worker_thread+0x53/0x420
 kthread+0x12f/0x150
 ret_from_fork+0x22/0x30

The root cause is truncate() may race with overwrite as below,
so that one reference count left in page can not guarantee the
page attaching in mapping tree all the time, after truncation,
later find_lock_page() may return NULL pointer.

- prepare_compress_overwrite
 - f2fs_pagecache_get_page
 - unlock_page
					- f2fs_setattr
					 - truncate_setsize
					  - truncate_inode_page
					   - delete_from_page_cache
 - find_lock_page

Fix this by avoiding referencing updated page.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2021-46982?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-46982?

Apply the vendor's patch.

## Is CVE-2021-46982 being exploited?

There is no known exploitation of CVE-2021-46982 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-2021-46982 and fix it if it is affected.

What it is: CVE-2021-46982 is a medium-severity vulnerability in Linux kernel, published on 28 Feb 2024. 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-2021-46982 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-2021-46982/ (Markdown: https://insights.sbomify.com/CVE-2021-46982/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-46982
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-46982
- OSV: https://osv.dev/vulnerability/CVE-2021-46982

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-46982/
Summaries are generated and may contain mistakes; the official description above is the record.