CVE-2021-46995 in Linux
Summary
by MITRE • 02/28/2024
In the Linux kernel, the following vulnerability has been resolved:
can: mcp251xfd: mcp251xfd_probe(): fix an error pointer dereference in probe
When we converted this code to use dev_err_probe() we accidentally removed a return. It means that if devm_clk_get() it will lead to an Oops when we call clk_get_rate() on the next line.
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Analysis
by VulDB Data Team • 12/06/2024
The vulnerability CVE-2021-46995 represents a critical error pointer dereference flaw in the Linux kernel's CAN (Controller Area Network) subsystem, specifically within the mcp251xfd driver implementation. This issue affects the mcp251xfd_probe() function which handles the initialization and probe operations for Microchip MCP251xFD CAN controller devices. The vulnerability stems from an improper code conversion that occurred when the driver was updated to utilize the dev_err_probe() helper function for error handling. During this refactoring process, a crucial return statement was inadvertently removed, creating a scenario where the driver fails to properly handle error conditions during device initialization.
The technical flaw manifests when the devm_clk_get() function is called during driver probe operations, which is a standard mechanism for acquiring clock resources for hardware devices. When this function fails to acquire the required clock resources, it returns an error pointer rather than a valid clock handle. The subsequent code execution continues without proper error checking, leading to a direct call to clk_get_rate() on what is actually an error pointer. This results in a kernel oops or system crash, as the kernel attempts to dereference an invalid memory address that represents the error condition rather than a legitimate clock resource handle. This type of vulnerability falls under CWE-476 which specifically addresses NULL pointer dereferences in software implementations.
The operational impact of this vulnerability is significant as it can cause system instability and potential denial of service conditions in embedded systems and automotive applications that rely on CAN communication. The MCP251xFD controllers are commonly used in automotive, industrial, and IoT devices where reliable network communication is critical. When a system crashes due to this vulnerability, it can lead to complete system lockups or require manual intervention to restore functionality. The vulnerability affects Linux kernel versions prior to the fix, making it a persistent risk for systems that have not been updated with the appropriate security patches. This issue particularly impacts automotive systems, industrial control networks, and any embedded device that depends on CAN bus communication for critical operations.
Mitigation strategies for this vulnerability primarily involve applying the official kernel security patch that corrects the error pointer handling in the mcp251xfd driver. System administrators should ensure that all affected Linux systems are updated to kernel versions that include the fix, typically kernel versions 5.12 or later. Additionally, organizations should implement robust patch management processes to maintain up-to-date kernel versions across their infrastructure. The fix addresses the underlying issue by restoring proper error handling logic that prevents the execution path from continuing when device resource acquisition fails. This vulnerability also highlights the importance of thorough testing during code refactoring processes, particularly when transitioning to new kernel helper functions like dev_err_probe(). From an ATT&CK framework perspective, this represents a privilege escalation vector through kernel exploitation, as it allows for system instability that could potentially be leveraged by malicious actors to cause persistent denial of service conditions or to gain unauthorized access to system resources.