CVE-2023-52492 in Linux
Summary
by MITRE • 03/11/2024
In the Linux kernel, the following vulnerability has been resolved:
dmaengine: fix NULL pointer in channel unregistration function
__dma_async_device_channel_register() can fail. In case of failure, chan->local is freed (with free_percpu()), and chan->local is nullified. When dma_async_device_unregister() is called (because of managed API or intentionally by DMA controller driver), channels are unconditionally unregistered, leading to this NULL pointer: [ 1.318693] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000d0
[...]
[ 1.484499] Call trace:
[ 1.486930] device_del+0x40/0x394
[ 1.490314] device_unregister+0x20/0x7c
[ 1.494220] __dma_async_device_channel_unregister+0x68/0xc0
Look at dma_async_device_register() function error path, channel device unregistration is done only if chan->local is not NULL.
Then add the same condition at the beginning of __dma_async_device_channel_unregister() function, to avoid NULL pointer issue whatever the API used to reach this function.
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Analysis
by VulDB Data Team • 12/04/2025
The vulnerability CVE-2023-52492 represents a critical NULL pointer dereference issue within the Linux kernel's DMA (Direct Memory Access) subsystem, specifically affecting the asynchronous device channel management functionality. This flaw exists in the interaction between the DMA engine's channel registration and unregistration processes, where improper error handling leads to system instability and potential denial of service conditions. The issue manifests when the __dma_async_device_channel_register() function encounters a failure condition, causing the channel's local data structure to be freed and nullified through the free_percpu() mechanism. However, subsequent calls to dma_async_device_unregister() do not properly validate the channel state before attempting cleanup operations, creating a scenario where a NULL pointer access occurs at virtual address 0x00000000000000d0 during device deletion operations.
The technical root cause of this vulnerability stems from inconsistent state management within the DMA subsystem's channel lifecycle handling. When channel registration fails, the system correctly frees the per-CPU local data structure and sets the channel's local pointer to NULL, which is the appropriate error recovery mechanism. However, the channel unregistration function __dma_async_device_channel_unregister() lacks this same defensive programming approach, executing unconditionally regardless of whether the channel data structure is valid or has been previously freed. This discrepancy creates a race condition and logic flaw where managed API calls or explicit controller driver invocations can trigger the NULL pointer dereference, leading to kernel oops and system crashes. The vulnerability specifically impacts the device_del() and device_unregister() functions in the kernel's device management subsystem, which are invoked during the cleanup process, ultimately causing the kernel to attempt accessing a NULL pointer at an offset within the channel structure.
The operational impact of CVE-2023-52492 extends beyond simple system crashes to encompass broader security and stability implications for Linux systems utilizing DMA operations. Systems running with DMA controllers that trigger this condition during normal operation or error recovery scenarios may experience unexpected kernel panics, requiring system reboots and potentially disrupting critical I/O operations. The vulnerability affects any Linux kernel version where the DMA engine subsystem is active, particularly impacting server environments, embedded systems, and devices relying heavily on DMA for high-performance data transfers. From a cybersecurity perspective, this vulnerability could be exploited by malicious actors to cause denial of service attacks against systems, as the NULL pointer dereference results in kernel crashes that can be reliably triggered through specific DMA controller operations or error conditions. The flaw aligns with CWE-476, which addresses NULL pointer dereference vulnerabilities, and represents a classic example of improper error handling in kernel space code that violates the principle of defensive programming.
Mitigation strategies for CVE-2023-52492 focus on implementing proper validation checks within the channel unregistration process to prevent access to freed memory structures. The recommended fix involves adding a NULL pointer check at the beginning of the __dma_async_device_channel_unregister() function, mirroring the existing pattern already implemented in the dma_async_device_register() error path. This defensive programming approach ensures that channel unregistration operations only proceed when valid channel data structures exist, preventing the kernel from attempting to access freed memory regions. System administrators should prioritize applying the kernel patches that implement this validation check, as the fix is straightforward and directly addresses the root cause without introducing compatibility issues. Additionally, monitoring systems should be configured to detect kernel oops messages or device unregister failures related to DMA operations, as these may indicate exploitation attempts or indicate that systems have not been properly patched. The fix aligns with ATT&CK technique T1499.004, which covers system shutdown/reboot attacks, by preventing the kernel panic conditions that could be leveraged for denial of service purposes. Organizations should also consider implementing runtime protections such as kernel hardening features and security modules that can detect and prevent exploitation attempts targeting similar NULL pointer dereference vulnerabilities in kernel subsystems.