# CVE-2024-42256: cifs: Fix server re-repick on subrequest retry

> A race condition in the Linux kernel CIFS module causes credit misaccounting during retries, potentially leading to system warnings and instability.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Aug 2024
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2024-42256, GHSA-jrcf-gr4j-p9gp, UBUNTU-CVE-2024-42256

## What is CVE-2024-42256?

CVE-2024-42256 is a high-severity vulnerability in Linux kernel, published on 8 Aug 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

cifs: Fix server re-repick on subrequest retry

When a subrequest is marked for needing retry, netfs will call
cifs_prepare_write() which will make cifs repick the server for the op
before renegotiating credits; it then calls cifs_issue_write() which
invokes smb2_async_writev() - which re-repicks the server.

If a different server is then selected, this causes the increment of
server->in_flight to happen against one record and the decrement to happen
against another, leading to misaccounting.

Fix this by just removing the repick code in smb2_async_writev().  As this
is only called from netfslib-driven code, cifs_prepare_write() should
always have been called first, and so server should never be NULL and the
preparatory step is repeated in the event that we do a retry.

The problem manifests as a warning looking something like:

 WARNING: CPU: 4 PID: 72896 at fs/smb/client/smb2ops.c:97 smb2_add_credits+0x3f0/0x9e0 [cifs]
 ...
 RIP: 0010:smb2_add_credits+0x3f0/0x9e0 [cifs]
 ...
  smb2_writev_callback+0x334/0x560 [cifs]
  cifs_demultiplex_thread+0x77a/0x11b0 [cifs]
  kthread+0x187/0x1d0
  ret_from_fork+0x34/0x60
  ret_from_fork_asm+0x1a/0x30

Which may be triggered by a number of different xfstests running against an
Azure server in multichannel mode.  generic/249 seems the most repeatable,
but generic/215, generic/249 and generic/308 may also show it.

## Which versions are affected by CVE-2024-42256?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2024-42256?

Apply the vendor's patch.

## Is CVE-2024-42256 being exploited?

There is no known exploitation of CVE-2024-42256 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-2024-42256 and fix it if it is affected.

What it is: CVE-2024-42256 is a high-severity vulnerability in Linux kernel, published on 8 Aug 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2024-42256 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-2024-42256/ (Markdown: https://insights.sbomify.com/CVE-2024-42256/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-42256
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-42256
- OSV: https://osv.dev/vulnerability/CVE-2024-42256

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-42256/
Summaries are generated and may contain mistakes; the official description above is the record.