CVE-2021-47237: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47237 is a memory leak vulnerability in the Linux kernel's hamradio network driver. The issue was discovered in the mkiss_close function where a netdevice was allocated and registered in mkiss_open(), but only unregistered and not properly freed in mkiss_close(). This vulnerability affects Linux kernel versions from 2.6.14 up to versions before 4.4.274, 4.9.274, 4.14.238, 4.19.196, and 5.4.128 (NVD).

The vulnerability stems from a missing free_netdev() call in the mkiss_close() function of the Linux kernel's hamradio driver. When a network device is created in mkiss_open(), it allocates memory using alloc_netdev_mqs() and registers the device. However, during cleanup in mkiss_close(), while the device is unregistered using unregister_netdev(), the allocated memory is not freed, leading to a memory leak. This was confirmed through syzbot testing which revealed multiple memory leak instances of varying sizes (4096, 96, 512, and 256 bytes) (Kernel Patch).

The vulnerability results in memory leaks of various sizes in the Linux kernel's hamradio driver. Each time the affected code path is executed, it leaks memory chunks of 4096, 96, 512, and 256 bytes, which over time could lead to system resource exhaustion. The CVSS v3.1 base score is 5.5 (Medium), indicating moderate severity with local access required (NVD).

The vulnerability requires local access and can be triggered through the mkiss driver operations. It was discovered through syzbot testing and has been demonstrated to consistently produce memory leaks when the affected code path is executed (Kernel Patch).

The vulnerability has been patched by adding a free_netdev(ax->dev) call in the mkiss_close() function. Users should upgrade to Linux kernel versions 4.4.274, 4.9.274, 4.14.238, 4.19.196, 5.4.128 or later which contain the fix (Kernel Patch).