[vbox-dev] Nullpointer access by USBDevIo thread in vusbUrbDoReapAsync

Alexander Boettcher alexander.boettcher at genode-labs.com
Wed Feb 28 11:28:21 UTC 2018

On 26.02.2018 11:06, Michal Necasek wrote:
>  Do you have some information about what triggers the crash? That is,
> what sort of USB configuration and what user action. As I mentioned, we
> have seen this problem before, but we don't know how to reproduce it.

I fear we haven't valuable information either. We just interactively
using a VM with USB Hid as input source. The USB related snippet in the
.vbox configuration files are:

<HID Pointing="USBTablet"/>
   <Controller name="OHCI" type="OHCI"/>

Maybe related, but has not be, we see during fresh VM installation
(using Debian 9.3 net installer) in our ported VirtualBox version that
the Linux guest complains that the USB controller is not responding and
the Linux guest driver gives up. Eventually we have a non working guest
mouse until next VM reboot.

Sorry for the poor informations,

>      Regards,
>        Michal
> On 2/13/2018 11:45 AM, Alexander Boettcher wrote:
>> Hello,
>> we encountered in our ported version of Virtualbox (originally in
>> 5.1.22, now in 5.1.32) from time to time a nullpointer crash in the
>> context of the USBDevIo thread (vusbUrbDoReapAsync() function).
>> We get around by the following patch [1] (original bug report at [2])
>> and all seems to work as expected.
>> The question from my side is, do you think this is valid fix ? Or do you
>> expect that pVUsbUrbNext should never be null and it maybe just becomes
>> null possibly due to our porting (timing, wrong usage etc.) ?
>> After looking through your svn repository at [0] it seems the issue also
>> could possibly exists there, since the code looks very similar regarding
>> the pVUsbUrbNext variable compared to 5.1.22/32.
>> Thanks for any thoughts,
>> Alexander Boettcher.
>> [0]
>> https://www.virtualbox.org/svn/vbox/trunk/src/VBox/Devices/USB/VUSBUrb.cpp
>> [1]
>> https://github.com/genodelabs/genode/commit/205c08bd9db9700f6a2629f97578e5fb9592fe94
>> [2] https://github.com/genodelabs/genode/issues/2612
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Alexander Boettcher
Genode Labs

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