CVE-2022-49568

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

KVM: Don't null dereference ops->destroy

A KVM device cleanup happens in either of two callbacks: 1) destroy() which is called when the VM is being destroyed; 2) release() which is called when a device fd is closed.

Most KVM devices use 1) but Book3s's interrupt controller KVM devices (XICS, XIVE, XIVE-native) use 2) as they need to close and reopen during the machine execution. The error handling in kvmioctlcreate_device() assumes destroy() is always defined which leads to NULL dereference as discovered by Syzkaller.

This adds a checks for destroy!=NULL and adds a missing release().

This is not changing kvmdestroydevices() as devices with defined release() should have been removed from the KVM devices list by then.