CVE-2024-49985

What it actually does

The flaw causes a deadlock on the clk prepare_lock mutex when an I2C transfer from a clock controller's .prepare callback triggers runtime resume of the stm32f7 I2C controller, which then calls clk_prepare_enable again.

Why it matters to the business

Systems using affected STM32F7-based hardware may experience hangs or instability during clock operations, disrupting embedded Linux deployments and time-sensitive applications with potential downtime in operational environments.

How an attack unfolds

An attacker triggers runtime suspend/resume cycles on the I2C bus while a clock controller attached to it performs prepare operations, leading to recursive mutex acquisition and deadlock; 2024 espionage and financially motivated actors have targeted similar Linux kernel race conditions for denial-of-service effects.

How to fix it

Update the Linux kernel to commit d6f1250a4d5773f447740b9fe37b8692105796d4 or later; on Rocky Linux 8 upgrade linuxptp to version 0:2.0-5.el8_4.1; avoid clock prepare/unprepare in runtime PM paths and use only clk_enable/clk_disable after initial probe.

How to confirm the fix worked

Confirm the fixed commit is present in the kernel tree or verify package version matches the listed fixed releases; test runtime suspend/resume cycles with an attached clock controller to ensure no deadlock occurs.

Typical attack path

1. Gain local access or control over attached clock hardware on an stm32f7 I2C bus
2. Trigger runtime suspend of the I2C controller
3. Initiate a clock prepare operation from the controller's clk_ops
4. Force an I2C transfer during resume that re-enters clk_prepare_enable
5. Deadlock on prepare_lock mutex

How to detect it

Inspect kernel logs for prepare_lock mutex deadlocks involving i2c-stm32f7 and clk prepare callbacks; correlate with runtime PM suspend/resume events on I2C buses.

What your security team should do

• Prioritize kernel and linuxptp updates on all STM32F7-based systems within standard patch windows
• Review embedded device configurations for external clock controllers on I2C buses
• Monitor kernel logs for mutex contention or I2C-related hangs as an interim detection measure