# CVE-2026-74463: i2c: jz4780: Cache host clock rate at probe to prevent CCF prepare_lock deadlock

> A race condition in the JZ4780 I2C driver causes a system deadlock, leading to denial of service for local attackers.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 19 Aug 2026
- **Also known as:** BELL-CVE-2026-74463, DEBIAN-CVE-2026-74463, GHSA-2xgc-rc56-qqm7, UBUNTU-CVE-2026-74463

## What is CVE-2026-74463?

CVE-2026-74463 is a vulnerability in Linux, published on 15 Aug 2026. 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:

i2c: jz4780: Cache host clock rate at probe to prevent CCF prepare_lock deadlock

Fix a severe AB/BA deadlock between the Common Clock Framework (CCF)
and the I2C adapter lock, which triggers when an I2C-controlled clock
generator client (like the Si5351) is registered or modified under the CCF.

During an i2c client clock (generator) frequency change, the CCF acquires its global
'prepare_lock' mutex and the driver calls i2c_transfer() to update the client's
chip registers, stalling for the adapter's I2C bus lock.

Concurrently, an independent, parallel transfer on the same bus (e.g., a GPIO
expander handling LEDs) can hold the I2C adapter lock. Inside this parallel
transfer path, jz4780_i2c_set_speed() calls clk_get_rate() on the host
controller's input clock to calculate bus timings. This call attempts to acquire
the blocked CCF 'prepare_lock', creating a circular dependency that freezes
the system.

The jz4780 host controller clock itself is static and never changes at runtime.

However, calling clk_get_rate() inside the active transfer path introduces
an unnecessary dependency on the CCF internal locks.

Eliminate this synchronous clk_get_rate() call from the active transfer
path by caching the static host peripheral clock rate once - inside the private
jz4780_i2c structure during jz4780_i2c_probe(). Update jz4780_i2c_set_speed()
to use this cached value, safely decoupling active I2C transactions from the
CCF internal locks without any risk of stale timings.

Assisted-by web based Google AI (pinpointing the bug and writing the message).

## Which versions are affected by CVE-2026-74463?


## How do I fix CVE-2026-74463?

Apply the vendor's patch.

## Is CVE-2026-74463 being exploited?

There is no known exploitation of CVE-2026-74463 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74463 and fix it if it is affected.

What it is: CVE-2026-74463 is a vulnerability in Linux, published on 15 Aug 2026. 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-2026-74463 in the wild and no public exploit code.

Affected product: Linux. 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-2026-74463/ (Markdown: https://insights.sbomify.com/CVE-2026-74463/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74463
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74463
- OSV: https://osv.dev/vulnerability/CVE-2026-74463

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74463/
Summaries are generated and may contain mistakes; the official description above is the record.