Re: [PATCH kernel] KVM: Don't null dereference ops->destroy

On 5/25/22 04:58, Alexey Kardashevskiy wrote:
>>>
> 
> 
> After reading
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id+de9b3ec8bdf60788e9e 
> and neighboring commits, it sounds that each create() should be paired 
> with either destroy() or release() but not necessarily both.

I agree, if release() is implemented then destroy() will never be called 
(except in error situations).

kvm_destroy_devices() should not be touched, except to add a WARN_ON 
perhaps.

> So I'm really not sure dummy handlers is a good idea. Thanks,

But in that case shouldn't kvm_ioctl_create_device also try 
ops->release, i.e.

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 6d971fb1b08d..f265e2738d46 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4299,8 +4299,11 @@ static int kvm_ioctl_create_device(struct kvm *kvm,
  		kvm_put_kvm_no_destroy(kvm);
  		mutex_lock(&kvm->lock);
  		list_del(&dev->vm_node);
+		if (ops->release)
+			ops->release(dev);
  		mutex_unlock(&kvm->lock);
-		ops->destroy(dev);
+		if (ops->destroy)
+			ops->destroy(dev);
  		return ret;
  	}

?

Paolo