CVE-2021-47121 in Linux
Summary
by MITRE • 03/15/2024
In the Linux kernel, the following vulnerability has been resolved:
net: caif: fix memory leak in cfusbl_device_notify
In case of caif_enroll_dev() fail, allocated link_support won't be assigned to the corresponding structure. So simply free allocated pointer in case of error.
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Analysis
by VulDB Data Team • 01/07/2025
The vulnerability identified as CVE-2021-47121 represents a memory leak flaw within the Linux kernel's CAIF (Cellular Advanced Frame Format) networking subsystem. This issue specifically affects the cfusbl_device_notify function which handles USB device notifications for CAIF communication channels. The CAIF protocol is designed to provide efficient data transmission over cellular networks and is commonly used in mobile devices and embedded systems requiring reliable network connectivity. The vulnerability occurs within the device enrollment process where the kernel attempts to establish communication links with USB-based CAIF devices.
The technical root cause of this memory leak stems from improper error handling within the caif_enroll_dev() function call. When this enrollment process fails, the kernel allocates memory for a link_support structure but fails to properly assign this allocated memory to the corresponding data structure. This creates a scenario where allocated memory remains unreferenced and cannot be freed during normal program execution. The flaw demonstrates a classic memory management error where resources are acquired but not properly released in error conditions, leading to gradual memory consumption that can eventually impact system performance and stability. This type of vulnerability falls under CWE-401, which specifically addresses improper release of memory after use, and represents a common pattern in kernel space programming where error paths are not adequately covered.
The operational impact of this vulnerability extends beyond simple memory consumption issues. While the immediate effect may appear benign, the cumulative effect of repeated memory leaks can lead to system resource exhaustion, particularly in embedded devices or systems with limited memory capacity. In mobile environments where CAIF is frequently utilized, this could result in degraded network performance, application instability, or even complete system crashes under sustained load conditions. The vulnerability is particularly concerning in automotive infotainment systems, industrial IoT devices, or any embedded platform where memory resources are constrained and system reliability is paramount. Attackers could potentially exploit this vulnerability to cause denial of service conditions by repeatedly triggering the error path, leading to progressive memory starvation.
Mitigation strategies for this vulnerability involve implementing proper error handling mechanisms that ensure all allocated memory is freed regardless of execution path. The fix requires modifying the cfusbl_device_notify function to explicitly check for allocation failures and ensure that any allocated link_support structures are properly released in error conditions. System administrators should prioritize applying kernel updates that contain the patched implementation, as this vulnerability affects the core networking subsystem. Additionally, monitoring memory usage patterns on systems utilizing CAIF functionality can help detect potential exploitation attempts. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security updates. The remediation aligns with ATT&CK technique T1499.001 which covers resource exhaustion attacks, and follows best practices outlined in the Linux kernel security guidelines for proper memory management in device drivers.