CVE-2021-47330 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
tty: serial: 8250: serial_cs: Fix a memory leak in error handling path
In the probe function, if the final 'serial_config()' fails, 'info' is leaking.
Add a resource handling path to free this memory.
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Analysis
by VulDB Data Team • 08/18/2025
The vulnerability identified as CVE-2021-47330 represents a memory leak in the Linux kernel's 8250 serial driver implementation within the serial_cs subsystem. This issue specifically affects the tty layer of the kernel where serial communication devices are managed. The flaw manifests during device probe operations when the kernel attempts to configure serial devices through the serial_config() function. When this configuration function fails, the kernel fails to properly release allocated memory resources, creating a persistent memory leak that can accumulate over time and potentially impact system stability and performance.
The technical root cause of this vulnerability lies in improper error handling within the probe function of the 8250 serial driver. During normal operation, the kernel allocates memory structures to manage serial device information and configuration parameters. However, when the serial_config() function returns an error status indicating configuration failure, the code path does not include cleanup routines to release the previously allocated memory. This memory leak occurs specifically in the context of serial communication device initialization where the kernel attempts to establish proper configuration parameters for serial devices. The flaw demonstrates a classic resource management issue where allocated memory is not properly deallocated during error conditions, violating fundamental principles of memory management in kernel space.
The operational impact of this vulnerability extends beyond simple memory consumption as it can lead to progressive system degradation over time. In systems with multiple serial devices or frequent device probing operations, the accumulation of leaked memory can result in reduced available system memory, increased memory pressure, and potentially system instability. The vulnerability affects systems running Linux kernel versions that include the 8250 serial driver implementation, particularly those utilizing serial communication hardware that requires configuration through the serial_cs subsystem. Attackers could potentially exploit this memory leak to cause denial of service conditions by triggering repeated device probe failures, though the direct security implications are limited compared to other kernel vulnerabilities.
The fix for CVE-2021-47330 involves implementing proper resource cleanup in the error handling path of the probe function. The solution requires adding explicit memory deallocation code to free the 'info' structure when serial_config() fails, ensuring that all allocated resources are properly released regardless of the function's success or failure status. This approach aligns with established security practices for kernel development and follows the principle of defensive programming where all allocated resources must be freed during error conditions. The fix addresses the underlying memory management issue by ensuring that the kernel's resource cleanup routines are executed consistently, preventing the accumulation of leaked memory that could otherwise impact system performance.
This vulnerability demonstrates characteristics consistent with CWE-401, which describes improper handling of memory allocation and deallocation in software systems. The issue falls under the category of resource leaks where the kernel fails to properly manage allocated memory during error conditions, potentially leading to resource exhaustion over time. The fix represents a standard defensive programming approach that ensures proper resource management throughout all code paths, including error handling scenarios. From an ATT&CK perspective, this vulnerability would be categorized under privilege escalation or denial of service techniques, as it affects kernel-level memory management and can impact system stability, though it does not directly enable arbitrary code execution or privilege escalation capabilities.
The resolution of CVE-2021-47330 through proper error handling and resource management practices highlights the importance of robust memory management in kernel space operations. This vulnerability serves as an example of how seemingly minor oversight in error handling can lead to cumulative resource exhaustion issues that affect system stability. The fix implementation ensures that all allocated resources are properly cleaned up regardless of execution path, demonstrating proper defensive programming practices that are essential for maintaining kernel stability and preventing resource-based denial of service conditions. System administrators should ensure that affected kernel versions are updated to include this memory leak fix to maintain optimal system performance and prevent potential stability issues related to resource accumulation.