CVE-2022-50081

This CVE ID has been rejected or withdrawn by its CVE Numbering Authority.

This CVE ID has been rejected or withdrawn by its CVE Numbering Authority.

In the Linux kernel, the following vulnerability has been resolved:

KVM: Unconditionally get a ref to /dev/kvm module when creating a VM

Unconditionally get a reference to the /dev/kvm module when creating a VM instead of using try_get_module(), which will fail if the module is in the process of being forcefully unloaded. The error handling when try_get_module() fails doesn't properly unwind all that has been done, e.g. doesn't call kvm_arch_pre_destroy_vm() and doesn't remove the VM from the global list. Not removing VMs from the global list tends to be fatal, e.g. leads to use-after-free explosions.

The obvious alternative would be to add proper unwinding, but the justification for using try_get_module(), "rmmod --wait", is completely bogus as support for "rmmod --wait", i.e. delete_module() without O_NONBLOCK, was removed by commit 3f2b9c9cdf38 ("module: remove rmmod --wait option.") nearly a decade ago.

It's still possible for try_get_module() to fail due to the module dying (more like being killed), as the module will be tagged MODULE_STATE_GOING by "rmmod --force", i.e. delete_module(..., O_TRUNC), but playing nice with forced unloading is an exercise in futility and gives a falsea sense of security. Using try_get_module() only prevents acquiring new references, it doesn't magically put the references held by other VMs, and forced unloading doesn't wait, i.e. "rmmod --force" on KVM is all but guaranteed to cause spectacular fireworks; the window where KVM will fail try_get_module() is tiny compared to the window where KVM is building and running the VM with an elevated module refcount.

Addressing KVM's inability to play nice with "rmmod --force" is firmly out-of-scope. Forcefully unloading any module taints kernel (for obvious reasons) and requires the kernel to be built with CONFIG_MODULE_FORCE_UNLOAD=y, which is off by default and comes with the amusing disclaimer that it's "mainly for kernel developers and desperate users". In other words, KVM is free to scoff at bug reports due to using "rmmod --force" while VMs may be running.

Rejected reason: This CVE ID has been rejected or withdrawn by its CVE Numbering Authority.

Rejected reason: This CVE ID has been rejected or withdrawn by its CVE Numbering Authority.

Rejected reason: This CVE ID has been rejected or withdrawn by its CVE Numbering Authority.