Commit 2ee37574 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
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KVM: Destroy I/O bus devices on unregister failure _after_ sync'ing SRCU 



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: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20210412222050.876100-2-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 24e7475f

virt/kvm/kvm_main.c

+7 −3
Original line number Diff line number Diff line
@@ -4646,7 +4646,13 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx, 
		new_bus->dev_count--;

		memcpy(new_bus->range + i, bus->range + i + 1,

				flex_array_size(new_bus, range, new_bus->dev_count - i));

	} else {

	}



	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);

	synchronize_srcu_expedited(&kvm->srcu);



	/* Destroy the old bus _after_ installing the (null) bus. */

	if (!new_bus) {

		pr_err("kvm: failed to shrink bus, removing it completely\n");

		for (j = 0; j < bus->dev_count; j++) {

			if (j == i)
@@ -4655,8 +4661,6 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx, 
		}

	}



	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);

	synchronize_srcu_expedited(&kvm->srcu);

	kfree(bus);

	return;

}