# CVE-2024-47691: f2fs: fix to avoid use-after-free in f2fs_stop_gc_thread()

> A race condition in the Linux kernel's f2fs filesystem allows a local attacker to trigger a use-after-free, potentially leading to code execution or privilege escalation.

- **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:** 21 Oct 2024
- **Updated:** 11 May 2026
- **Also known as:** AZL-50882, BELL-CVE-2024-47691, DEBIAN-CVE-2024-47691, GHSA-gc96-qrrv-3724, ROOT-OS-DEBIAN-11-CVE-2024-47691, ROOT-OS-DEBIAN-12-CVE-2024-47691, ROOT-OS-UBUNTU-2204-CVE-2024-47691, UBUNTU-CVE-2024-47691

## What is CVE-2024-47691?

CVE-2024-47691 is a high-severity use after free vulnerability in Linux kernel, published on 21 Oct 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: fix to avoid use-after-free in f2fs_stop_gc_thread()

syzbot reports a f2fs bug as below:

 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 print_report+0xe8/0x550 mm/kasan/report.c:491
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
 __refcount_add include/linux/refcount.h:184 [inline]
 __refcount_inc include/linux/refcount.h:241 [inline]
 refcount_inc include/linux/refcount.h:258 [inline]
 get_task_struct include/linux/sched/task.h:118 [inline]
 kthread_stop+0xca/0x630 kernel/kthread.c:704
 f2fs_stop_gc_thread+0x65/0xb0 fs/f2fs/gc.c:210
 f2fs_do_shutdown+0x192/0x540 fs/f2fs/file.c:2283
 f2fs_ioc_shutdown fs/f2fs/file.c:2325 [inline]
 __f2fs_ioctl+0x443a/0xbe60 fs/f2fs/file.c:4325
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:907 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The root cause is below race condition, it may cause use-after-free
issue in sbi->gc_th pointer.

- remount
 - f2fs_remount
  - f2fs_stop_gc_thread
   - kfree(gc_th)
				- f2fs_ioc_shutdown
				 - f2fs_do_shutdown
				  - f2fs_stop_gc_thread
				   - kthread_stop(gc_th->f2fs_gc_task)
   : sbi->gc_thread = NULL;

We will call f2fs_do_shutdown() in two paths:
- for f2fs_ioc_shutdown() path, we should grab sb->s_umount semaphore
for fixing.
- for f2fs_shutdown() path, it's safe since caller has already grabbed
sb->s_umount semaphore.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2024-47691?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-47691?

Apply the vendor's patch.

## Is CVE-2024-47691 being exploited?

There is no known exploitation of CVE-2024-47691 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-2024-47691 and fix it if it is affected.

What it is: CVE-2024-47691 is a high-severity use after free vulnerability in Linux kernel, published on 21 Oct 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-2024-47691 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-2024-47691/ (Markdown: https://insights.sbomify.com/CVE-2024-47691/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-47691
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-47691
- OSV: https://osv.dev/vulnerability/CVE-2024-47691

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-47691/
Summaries are generated and may contain mistakes; the official description above is the record.