I have discovered a problem with the VirtualBox virtio-net network driver
leads to a lockup of the host machine's kernel and the need for a hard
to make it working again. The bug had been reported to the VirtualBox bug
tracker 8 days ago (https://www.virtualbox.org/ticket/11863), with the
reaction from Oracle support (i.e. none).
The bug can be reproduced easily as follows:
- The host system is a 64-bit Linux (tested with Ubuntu 12.04 LTS and
13.04). Did not try 32 bit.
- VirtualBox is the latest version 4.2.12 (using Oracle's Ubuntu
- Create a new VM, use e.g. Kubuntu live CD image (32 or 64 bit, makes no
difference). No disk needed.
- Network adapter is: Bridged, Adapter Type: virtio-net.
Boot the system, ensure that network is working.
- tracepath 126.96.36.199
Now, the virtual machine locks up and the host machine's kernel seems to
at least one core blocked. The host machine's console output is "BUG: soft
lockup - CPU #2 stuck for 22s ...". Also, the network on the host machine
not work any more. For example, "ifconfig" just hangs.
- To recover the host machine, it needs a hard reset. "sudo reboot", etc.
not work, since the kernel seems to hang.
This bug is critical, since it makes the host machine's network unusable
(particularly, if the host system is at a remote location), and it is very
easy to trigger with just a simple, standard "tracepath" call inside a
machine. It is therefore trivial for a normal user in such a machine to
trigger a denial of service. I did no further investigation of the problem
yet, but if it is related to the path MTU discovery by tracepath, it might
possible to trigger it by a lot of other software as well.
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