CVE-2021-47100: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47100 is a Use-After-Free (UAF) vulnerability in the Linux kernel's IPMI subsystem that occurs when uninstalling ipmi_si and ipmi_msghandler modules. The vulnerability was discovered in Linux kernel versions from 4.15 up to 5.16-rc6 (NVD).

The vulnerability occurs due to a race condition during module unloading. When ipmi_si module is removed, it triggers ipmi_unregister_smi() which leads to a cleanup work being scheduled. If the ipmi_msghandler module is unloaded before this cleanup work executes, it results in accessing freed memory when the cleanup work eventually runs. The vulnerability has a CVSS v3.1 Base Score of 5.5 (Medium) with vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

When successfully exploited, this vulnerability can cause a system crash due to accessing freed memory. The issue manifests as a kernel panic when attempting to access the bmc_device_type structure after it has been freed during the ipmi_msghandler module unload (Kernel Patch).

The vulnerability requires local access and the ability to load/unload kernel modules. It can be triggered by uninstalling the ipmi_si module followed by the ipmi_msghandler module in quick succession (Kernel Patch).

The issue has been fixed by using 'remove_work_wq' instead of 'system_wq' for scheduling the cleanup work. Users should update to patched kernel versions. The fix was implemented in the kernel commit ffb76a86f8096a8206be03b14adda6092e18e275 (Kernel Patch).