CVE-2021-47231: 
Linux Kernel vulnerability analysis and mitigation

A memory leak vulnerability (CVE-2021-47231) was discovered in the Linux kernel's SocketCAN driver for Microchip CAN BUS Analyzer Tool. The issue was identified in the mcba_usb driver where coherent buffers allocated in mcba_usb_start() were not being properly freed (Kernel Git).

The vulnerability stems from 20 coherent buffers being allocated in mcba_usb_start() without proper deallocation mechanisms. In the callback function, the URB is simply resubmitted, and in the disconnect function, URBs are killed without setting URB_FREE_BUFFER flag. Additionally, this flag cannot be used with coherent buffers. The issue was confirmed through kmemleak detection showing 20 new suspected memory leaks (Kernel Git).

The vulnerability results in memory leaks in the kernel space, which over time could lead to resource exhaustion. This was evidenced by the system log showing multiple memory leaks detected by kmemleak after device disconnection (Kernel Git).

The vulnerability was discovered and reported by Syzbot, Google's kernel fuzzing bot. While the issue requires local access and interaction with the CAN bus hardware, it can be triggered through normal device operations such as disconnecting the CAN bus analyzer (Kernel Git).

The issue has been fixed by explicitly freeing the allocated buffers using usb_free_coherent(). The fix involves tracking the allocated buffers and their DMA addresses in the driver's private structure and properly cleaning them up in the mcba_urb_unlink function (Kernel Git).