[PATCH kernel v2] KVM: Don't null dereference ops->destroy

[PATCH kernel v2] KVM: Don't null dereference ops->destroy

[Alexey Kardashevskiy]

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 kvm_ioctl_create_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 kvm_destroy_devices() as devices with defined
release() should have been removed from the KVM devices list by then.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v2:
* do not touch kvm_destroy_devices
* call release() in the error path
---
 virt/kvm/kvm_main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f30bb8c16f26..e1c4bca95040 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;
 	}
 
-- 
2.30.2

Re: [PATCH kernel v2] KVM: Don't null dereference ops->destroy

[Paolo Bonzini]

On 6/1/22 03:43, Alexey Kardashevskiy wrote:
> 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 kvm_ioctl_create_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 kvm_destroy_devices() as devices with defined
> release() should have been removed from the KVM devices list by then.
> 
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Queued, thanks.

Paolo

> ---
> Changes:
> v2:
> * do not touch kvm_destroy_devices
> * call release() in the error path
> ---
>   virt/kvm/kvm_main.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index f30bb8c16f26..e1c4bca95040 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;
>   	}
>   

Queued, thanks.

Paolo