KVM: x86/xen: Fix eventfd error handling in kvm_xen_eventfd_assign()

Should not call eventfd_ctx_put() in case of error.

Fixes: 2fd6df2f ("KVM: x86/xen: intercept EVTCHNOP_send from guests")
Reported-by: syzbot+6f0c896c5a9449a10ded@syzkaller.appspotmail.com
Signed-off-by: Eiichi Tsukata <eiichi.tsukata@nutanix.com>
Message-Id: <20221028092631.117438-1-eiichi.tsukata@nutanix.com>
[Introduce new goto target instead. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/xen.c

@@ -1666,18 +1666,18 @@ static int kvm_xen_eventfd_assign(struct kvm *kvm,
 	case EVTCHNSTAT_ipi:
 		/* IPI  must map back to the same port# */
 		if (data->u.evtchn.deliver.port.port != data->u.evtchn.send_port)
-			goto out; /* -EINVAL */
+			goto out_noeventfd; /* -EINVAL */
 		break;
 
 	case EVTCHNSTAT_interdomain:
 		if (data->u.evtchn.deliver.port.port) {
 			if (data->u.evtchn.deliver.port.port >= max_evtchn_port(kvm))
-				goto out; /* -EINVAL */
+				goto out_noeventfd; /* -EINVAL */
 		} else {
 			eventfd = eventfd_ctx_fdget(data->u.evtchn.deliver.eventfd.fd);
 			if (IS_ERR(eventfd)) {
 				ret = PTR_ERR(eventfd);
-				goto out;
+				goto out_noeventfd;
 			}
 		}
 		break;
@@ -1717,6 +1717,7 @@ static int kvm_xen_eventfd_assign(struct kvm *kvm,
 out:
 	if (eventfd)
 		eventfd_ctx_put(eventfd);
+out_noeventfd:
 	kfree(evtchnfd);
 	return ret;
 }