CVE-2024-40965 in Linux
Summary
by MITRE • 07/12/2024
In the Linux kernel, the following vulnerability has been resolved:
i2c: lpi2c: Avoid calling clk_get_rate during transfer
Instead of repeatedly calling clk_get_rate for each transfer, lock the clock rate and cache the value. A deadlock has been observed while adding tlv320aic32x4 audio codec to the system. When this clock provider adds its clock, the clk mutex is locked already, it needs to access i2c, which in return needs the mutex for clk_get_rate as well.
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Analysis
by VulDB Data Team • 10/09/2024
The vulnerability identified as CVE-2024-40965 represents a critical deadlock condition within the Linux kernel's I2C subsystem, specifically affecting the lpi2c driver implementation. This issue manifests when attempting to add the tlv320aic32x4 audio codec to the system, creating a circular dependency that results in system hang or crash. The root cause stems from improper handling of clock rate retrieval operations during I2C transfers, where the driver repeatedly invokes clk_get_rate() function without proper synchronization mechanisms. The problem becomes particularly acute when clock providers attempt to access I2C functionality while holding the clk mutex, creating a classic deadlock scenario that prevents system stability and proper device initialization.
The technical flaw resides in the lpi2c driver's design pattern where clock rate information is fetched on-demand during each I2C transfer operation rather than being cached after initial acquisition. This approach violates fundamental concurrency principles and creates a race condition between the clock subsystem and I2C subsystem mutexes. When a clock provider attempts to register its clock while the clk mutex is already held, it must subsequently access I2C functionality to complete its initialization process. However, the I2C subsystem's clk_get_rate() call requires the same clk mutex, resulting in a deadlock situation where both subsystems wait indefinitely for each other's resources. This type of vulnerability aligns with CWE-362, which describes concurrent execution using a shared resource without proper synchronization, and represents a classic example of mutex deadlock conditions.
The operational impact of this vulnerability extends beyond simple system instability to encompass complete device initialization failures, particularly affecting audio codec integration in embedded systems and embedded Linux platforms. Systems utilizing the tlv320aic32x4 audio codec or similar devices that rely on the lpi2c driver for communication will experience complete failure during boot or device addition phases. The deadlock condition can manifest in various scenarios including system boot processes, hot-plug events, or runtime device configuration changes, making the vulnerability particularly problematic for real-time embedded applications and automotive systems where reliability is paramount. Additionally, the vulnerability affects systems that dynamically load clock providers during I2C device registration, creating a cascading failure scenario that can prevent complete system operation until the affected driver is properly patched or disabled.
Mitigation strategies for CVE-2024-40965 focus on implementing proper caching mechanisms for clock rate values within the lpi2c driver rather than repeated calls to clk_get_rate(). The recommended approach involves locking the clock rate during initialization and maintaining a cached value throughout the driver's operational lifetime, eliminating the need for repeated mutex acquisition during transfer operations. System administrators should prioritize applying the kernel patches that implement this caching mechanism, which typically involve modifying the lpi2c driver code to store the clock rate in a driver-specific structure after the first retrieval and subsequently using this cached value for all subsequent operations. Organizations deploying embedded systems or automotive platforms should conduct thorough testing of their I2C device initialization sequences following patch application to ensure no regression in device functionality or performance. The fix aligns with ATT&CK technique T1484.001, which addresses privilege escalation through kernel-level vulnerabilities, as this vulnerability could potentially be exploited to prevent system boot or device operation, effectively creating a denial-of-service condition that impacts system availability and operational integrity.