CVE-2021-47073: 
Linux Kernel vulnerability analysis and mitigation

CVE-2021-47073 affects the Linux kernel's Dell SMBIOS WMI driver implementation. The vulnerability was discovered in the platform/x86 dell-smbios-wmi module, where an unconditional driver unregistration could lead to a kernel oops when removing the dell_smbios module (Kernel Commit).

The vulnerability occurs because init_dell_smbios_wmi() only registers the dell_smbios_wmi_driver on systems where the Dell WMI interface is supported, while exit_dell_smbios_wmi() unregisters it unconditionally. This mismatch in registration/unregistration logic leads to a kernel oops when attempting to remove the dell_smbios module on systems where the driver was not previously registered (Kernel Commit).

When triggered, this vulnerability results in a kernel oops, which can cause system instability. The issue manifests as an "Unexpected driver unregister!" warning message in the kernel log, followed by a stack trace (Kernel Commit).

The vulnerability can be triggered by attempting to remove the dell_smbios module (using rmmod) on affected systems where the Dell WMI interface is not supported (Kernel Commit).

The issue has been fixed by making the unregister operation conditional on the same check used during registration. The fix has been implemented in various Linux distributions, including Ubuntu where it has been patched in multiple kernel versions: 5.4.0-80.90 for focal (20.04 LTS) and 4.15.0-151.157 for bionic (18.04 LTS) (Ubuntu Security).