# CVE-2025-37999: fs/erofs/fileio: call erofs_onlinefolio_split() after bio_add_folio()

> A logic error in the Linux kernel EROFS fileio module causes folios to remain locked indefinitely, leading to a denial of service when readahead is triggered.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/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:** 29 May 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-37999, DEBIAN-CVE-2025-37999, GHSA-7qr6-vjfq-429r, UBUNTU-CVE-2025-37999

## What is CVE-2025-37999?

CVE-2025-37999 is a medium-severity denial of service vulnerability in Linux kernel, published on 29 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:

fs/erofs/fileio: call erofs_onlinefolio_split() after bio_add_folio()

If bio_add_folio() fails (because it is full),
erofs_fileio_scan_folio() needs to submit the I/O request via
erofs_fileio_rq_submit() and allocate a new I/O request with an empty
`struct bio`.  Then it retries the bio_add_folio() call.

However, at this point, erofs_onlinefolio_split() has already been
called which increments `folio->private`; the retry will call
erofs_onlinefolio_split() again, but there will never be a matching
erofs_onlinefolio_end() call.  This leaves the folio locked forever
and all waiters will be stuck in folio_wait_bit_common().

This bug has been added by commit ce63cb62d794 ("erofs: support
unencoded inodes for fileio"), but was practically unreachable because
there was room for 256 folios in the `struct bio` - until commit
9f74ae8c9ac9 ("erofs: shorten bvecs[] for file-backed mounts") which
reduced the array capacity to 16 folios.

It was now trivial to trigger the bug by manually invoking readahead
from userspace, e.g.:

 posix_fadvise(fd, 0, st.st_size, POSIX_FADV_WILLNEED);

This should be fixed by invoking erofs_onlinefolio_split() only after
bio_add_folio() has succeeded.  This is safe: asynchronous completions
invoking erofs_onlinefolio_end() will not unlock the folio because
erofs_fileio_scan_folio() is still holding a reference to be released
by erofs_onlinefolio_end() at the end.

## Which versions are affected by CVE-2025-37999?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-37999?

Apply the vendor's patch.

## Is CVE-2025-37999 being exploited?

There is no known exploitation of CVE-2025-37999 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-2025-37999 and fix it if it is affected.

What it is: CVE-2025-37999 is a medium-severity denial of service vulnerability in Linux kernel, published on 29 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-2025-37999 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-2025-37999/ (Markdown: https://insights.sbomify.com/CVE-2025-37999/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-37999
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-37999
- OSV: https://osv.dev/vulnerability/CVE-2025-37999

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-37999/
Summaries are generated and may contain mistakes; the official description above is the record.