KVM: Destroy I/O bus devices on unregister failure _after_ sync'ing SRCU

mainline inclusion
from mainline-v5.13-rc1
commit 2ee37574
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I94VO4


CVE: CVE-2021-47061

--------------------------------

If allocating a new instance of an I/O bus fails when unregistering a
device, wait to destroy the device until after all readers are guaranteed
to see the new null bus.  Destroying devices before the bus is nullified
could lead to use-after-free since readers expect the devices on their
reference of the bus to remain valid.

Fixes: f6588660 ("KVM: fix memory leak in kvm_io_bus_unregister_dev()")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210412222050.876100-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Conflicts:
	virt/kvm/kvm_main.c
Signed-off-by: Liu Shixin <liushixin2@huawei.com>