CVE-2024-36940 in Linux
Summary
by MITRE • 05/30/2024
In the Linux kernel, the following vulnerability has been resolved:
pinctrl: core: delete incorrect free in pinctrl_enable()
The "pctldev" struct is allocated in devm_pinctrl_register_and_init(). It's a devm_ managed pointer that is freed by devm_pinctrl_dev_release(), so freeing it in pinctrl_enable() will lead to a double free.
The devm_pinctrl_dev_release() function frees the pindescs and destroys the mutex as well.
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Analysis
by VulDB Data Team • 01/11/2025
The vulnerability described in CVE-2024-36940 represents a critical double free error within the Linux kernel's pinctrl subsystem, specifically affecting the pinctrl_enable() function. This issue occurs in the kernel's pin control framework which manages the configuration of hardware pins for various device functions. The pinctrl subsystem is fundamental to embedded systems and mobile devices where hardware pin multiplexing is essential for proper device operation. When a pinctrl device is registered through devm_pinctrl_register_and_init(), the kernel allocates a pctldev structure using device managed memory allocation functions. This allocation mechanism ensures proper cleanup during device removal or system shutdown, with the devm_ family of functions automatically handling memory deallocation through their respective release callbacks. The problem arises from an incorrect implementation in the pinctrl_enable() function that attempts to manually free the same pctldev structure that is already scheduled for automatic cleanup by devm_pinctrl_dev_release(). This fundamental error violates the core principles of memory management in kernel space, where double freeing of memory blocks can lead to severe system instability and potential security exploits.
The technical flaw manifests as a direct violation of proper memory management practices within the Linux kernel's device management subsystem. The pctldev structure, which contains pin descriptor information and associated metadata, is allocated using devm_kzalloc() or similar device-managed allocation functions in devm_pinctrl_register_and_init(). This allocation is specifically designed to be automatically cleaned up when the device is removed or during system shutdown through the devm_pinctrl_dev_release() function. However, the pinctrl_enable() function incorrectly attempts to free this same structure directly, creating a scenario where the same memory block is freed twice. The devm_pinctrl_dev_release() function not only frees the pindescs array but also destroys the mutex associated with the pin control device, making the double free operation particularly dangerous. This type of memory corruption vulnerability is classified as a CWE-415 Double Free, which is a well-known class of vulnerabilities that can be exploited to gain arbitrary code execution or cause system crashes. The vulnerability is particularly concerning in embedded systems where the kernel's memory management is more tightly constrained and where such errors can lead to complete system failure or compromise.
The operational impact of this vulnerability extends beyond simple system crashes, potentially enabling privilege escalation and denial of service conditions that can affect the entire system's stability. When the pinctrl_enable() function executes the incorrect free operation, it can cause memory corruption that may result in kernel oops, system panics, or more insidiously, provide an attacker with opportunities to manipulate kernel memory structures. The vulnerability affects systems that utilize the Linux kernel's pinctrl subsystem, which is prevalent in mobile devices, embedded systems, and any platform that requires pin multiplexing for hardware peripherals. Attackers could potentially exploit this vulnerability by triggering the pinctrl_enable() function through specific device operations or by manipulating pin control device registration sequences. The double free condition creates a memory layout that can be manipulated to redirect execution flow or corrupt kernel data structures, making this a serious security concern that could be leveraged for privilege escalation attacks. The vulnerability is particularly dangerous because it occurs during normal device operation when pin control is enabled, making it difficult to detect and potentially exploitable in both kernel-space and user-space attack scenarios.
Mitigation strategies for this vulnerability require immediate kernel updates from vendors and system administrators to ensure the patched version is deployed across affected systems. The fix implemented in the kernel resolves the double free issue by removing the incorrect free operation from pinctrl_enable() and allowing the device manager to handle all memory cleanup appropriately. System administrators should prioritize patching systems that utilize pin control functionality, particularly those in embedded environments or mobile devices where such vulnerabilities can have severe operational consequences. The recommended approach involves monitoring security advisories from kernel maintainers and applying patches through standard update mechanisms. Additionally, organizations should consider implementing runtime monitoring solutions that can detect anomalous memory behavior patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper resource management in kernel space and reinforces the need for thorough code reviews of device management subsystems. Security teams should also consider implementing automated testing procedures that specifically target memory management functions within kernel subsystems to identify similar issues before they can be exploited in production environments. This vulnerability serves as a reminder of the critical importance of proper device management and memory allocation practices in kernel development, where even seemingly minor implementation errors can have significant security implications.