CVE-2023-52855 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
usb: dwc2: fix possible NULL pointer dereference caused by driver concurrency
In _dwc2_hcd_urb_enqueue(), "urb->hcpriv = NULL" is executed without holding the lock "hsotg->lock". In _dwc2_hcd_urb_dequeue():
spin_lock_irqsave(&hsotg->lock, flags); ... if (!urb->hcpriv) {
dev_dbg(hsotg->dev, "## urb->hcpriv is NULL ##\n"); goto out; } rc = dwc2_hcd_urb_dequeue(hsotg, urb->hcpriv); // Use urb->hcpriv ... out: spin_unlock_irqrestore(&hsotg->lock, flags);
When _dwc2_hcd_urb_enqueue() and _dwc2_hcd_urb_dequeue() are concurrently executed, the NULL check of "urb->hcpriv" can be executed before "urb->hcpriv = NULL". After urb->hcpriv is NULL, it can be used in the function call to dwc2_hcd_urb_dequeue(), which can cause a NULL pointer dereference.
This possible bug is found by an experimental static analysis tool developed by myself. This tool analyzes the locking APIs to extract function pairs that can be concurrently executed, and then analyzes the instructions in the paired functions to identify possible concurrency bugs including data races and atomicity violations. The above possible bug is reported, when my tool analyzes the source code of Linux 6.5.
To fix this possible bug, "urb->hcpriv = NULL" should be executed with holding the lock "hsotg->lock". After using this patch, my tool never reports the possible bug, with the kernelconfiguration allyesconfig for x86_64. Because I have no associated hardware, I cannot test the patch in runtime testing, and just verify it according to the code logic.
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Analysis
by VulDB Data Team • 06/20/2025
The vulnerability described in CVE-2023-52855 represents a critical concurrency issue within the Linux kernel's USB device driver subsystem, specifically affecting the DesignWare USB2 Host Controller driver implementation. This flaw manifests as a potential NULL pointer dereference that occurs due to improper synchronization between concurrent execution paths within the driver's USB request block handling mechanisms. The issue resides in the dwc2_hcd_urb_enqueue function where the hcpriv field of a USB request block is set to NULL without proper locking mechanisms, creating a race condition with the corresponding dwc2_hcd_urb_dequeue function that performs a NULL check before using the hcpriv value.
The technical implementation of this vulnerability stems from the absence of proper lock acquisition during the assignment of NULL to urb->hcpriv in the enqueue function, while the dequeue function correctly employs spin_lock_irqsave operations to protect access to shared data structures. This asymmetry in locking creates a temporal window where a concurrent execution path can read the NULL value after it has been assigned but before the lock is acquired, leading to a scenario where the subsequent function call dwc2_hcd_urb_dequeue(hsotg, urb->hcpriv) attempts to dereference a NULL pointer. The static analysis tool that identified this issue employs sophisticated techniques to analyze locking APIs and identify function pairs that may execute concurrently, then examines the instruction sequences within these functions to detect potential data races and atomicity violations that could lead to system instability or security implications.
The operational impact of this vulnerability extends beyond simple system crashes, potentially creating conditions that could be exploited by malicious actors to cause denial of service attacks or system instability within embedded systems and devices that rely heavily on USB connectivity. This vulnerability affects systems running Linux kernel versions where the dwc2 USB driver is utilized, particularly those implementing USB host controller functionality using DesignWare USB2 controllers. The race condition could be triggered through normal USB operations involving concurrent submission and cancellation of USB requests, making it particularly concerning for systems where USB devices are frequently connected and disconnected or where high-throughput USB operations are common. The vulnerability aligns with CWE-362, which identifies concurrent execution using locks and other synchronization mechanisms as a potential source of data races, and demonstrates characteristics that could be categorized under ATT&CK technique T1499.001 for network denial of service attacks through system instability.
The mitigation strategy for this vulnerability involves implementing proper locking semantics throughout the affected code path by ensuring that the assignment of NULL to urb->hcpriv in the enqueue function occurs while holding the hsotg->lock spinlock. This approach maintains the atomicity of the operation and prevents the race condition between the enqueue and dequeue functions. The fix requires modifying the dwc2_hcd_urb_enqueue function to acquire the lock before setting urb->hcpriv to NULL, thereby ensuring that all operations involving the hcpriv field are properly synchronized. This solution follows established best practices for concurrent programming in kernel space where shared data structures must be protected by appropriate synchronization primitives. The static analysis tool's verification process confirms that this modification resolves the identified race condition, though the lack of hardware testing limitations means that real-world validation of the patch's effectiveness in production environments remains incomplete, emphasizing the importance of thorough testing in actual deployment scenarios.