KVM: fix memory leak in kvm_io_bus_unregister_dev()

when kmalloc() fails in kvm_io_bus_unregister_dev(), before removing
the bus, we should iterate over all other devices linked to it and call
kvm_iodevice_destructor() for them

Fixes: 90db1043 ("KVM: kvm_io_bus_unregister_dev() should never fail")
Cc: stable@vger.kernel.org
Reported-and-tested-by: syzbot+f196caa45793d6374707@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=f196caa45793d6374707Signed-off-by: Rustam Kovhaev <rkovhaev@gmail.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20200907185535.233114-1-rkovhaev@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

virt/kvm/kvm_main.c

@@ -4332,7 +4332,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
 			       struct kvm_io_device *dev)
 {
-	int i;
+	int i, j;
 	struct kvm_io_bus *new_bus, *bus;
 
 	bus = kvm_get_bus(kvm, bus_idx);
@@ -4349,17 +4349,20 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
 
 	new_bus = kmalloc(struct_size(bus, range, bus->dev_count - 1),
 			  GFP_KERNEL_ACCOUNT);
-	if (!new_bus)  {
-		pr_err("kvm: failed to shrink bus, removing it completely\n");
-		goto broken;
-	}
-
+	if (new_bus) {
 		memcpy(new_bus, bus, sizeof(*bus) + i * sizeof(struct kvm_io_range));
 		new_bus->dev_count--;
 		memcpy(new_bus->range + i, bus->range + i + 1,
 		       (new_bus->dev_count - i) * sizeof(struct kvm_io_range));
+	} else {
+		pr_err("kvm: failed to shrink bus, removing it completely\n");
+		for (j = 0; j < bus->dev_count; j++) {
+			if (j == i)
+				continue;
+			kvm_iodevice_destructor(bus->range[j].dev);
+		}
+	}
 
-broken:
 	rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
 	synchronize_srcu_expedited(&kvm->srcu);
 	kfree(bus);