Recently, a patch was released for the Linux kernel by Takashi Iwai from SUSE to address a crucial flaw in the USB-audio driver that could result in out-of-bounds memory reads.
The Linux kernel’s USB-audio driver possesses a vulnerability in out-of-bounds access, potentially enabling a physical intruder to exploit a malicious USB device for escalating privileges, manipulating system memory, or executing arbitrary code.
Enhancing the stability and security of systems utilizing USB audio devices, a fix was introduced by Greg Kroah-Hartman of the Linux Foundation on December 14, 2024.
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Functionality of the Attack
The vulnerability emerges when a USB audio device presents a descriptor with a bLength value shorter than the anticipated structure size. Initially, the driver assumed the descriptor was complete in the source code and attempted to access its fields, like clock IDs or pin arrays.
If the descriptor was cut off due to a hardware defect or intentional tampering, the driver could overstep the allocated memory buffer into unintended adjacent spaces.
This out-of-bounds read could expose confidential data from the kernel’s memory, such as pointers or user data, or provoke a system crash by accessing invalid memory locations.
In an extreme case, a skilled attacker could potentially combine this flaw with other exploits to elevate privileges or execute arbitrary code, necessitating precise control over the USB device and additional vulnerabilities.
Iwai, in the included notes, termed this update as a proactive measure to protect Linux systems utilizing USB audio hardware. The fix has been merged into stable kernel branches, ensuring enhanced security for users on various distributions.
The clock selector descriptor, containing a variable-length array and supplementary fields, undergoes more rigorous validation to accommodate its complexity across USB Audio Class (UAC) versions 2 and 3.
Fortifying USB Audio Security
The root of the issue lies in the driver’s neglect to verify the bLength field of clock descriptors provided by USB audio devices.
In the absence of these validations, an inadequately sized or maliciously crafted descriptor could provoke memory access beyond the allocated limits, potentially leading to system crashes or susceptibility to exploitation.
Initially reported by Benoît Sevens from Google, this vulnerability underscores its critical nature within the broader Linux community.
The identified patch, marked as commit ab011f7439d9bbfd34fd3b9cef4b2d6d952c9bb9, introduces stringent checks within the clock descriptor validation functions.
Though the alteration is minor, involving just 24 lines in the sound/usb/clock.c file, its significance is notable for audiophiles, developers, and businesses reliant on Linux for audio processing.
Users are advised to update their kernels with this patch, accessible for download as linux-ab011f7439d9bbfd34fd3b9cef4b2d6d952c9bb9.tar.gz.
This development emphasizes the continual dedication of the Linux community to promptly tackle vulnerabilities and maintain the system’s reputation for durability and dependability.