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

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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@xxxxxxxxxx>
Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>

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




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