won't open host network interface

[Andrew Schulman]

I have the dreaded "Failed to open host network interface" problem. I'm using Host Interface networking on a Linux host (Debian AMD64, custom 2.6.24 kernel), with a tap device named vbox0 bridged to lan:

$ brctl show lan
bridge name     bridge id               STP enabled     interfaces
lan             8000.00161711ac84       no              lan0
                                                        vbox0

When user andrex tries to start the VM, it fails with the following VBox.log:

00:00:15.216 VirtualBox 1.6.2 r31466 linux.amd64 (May 31 2008 17:30:23) release log
00:00:15.216 Log opened 2008-07-02T15:28:43.546408000Z
00:00:15.230 VRDP: TCP server listening on port 33891.
00:00:15.238 SUP: Loaded VMMR0.r0 (/usr/lib/virtualbox/VMMR0.r0) at 0xffffffff88d44900 -
  ModuleInit at ffffffff88d50590 and ModuleTerm at ffffffff88d50560
00:00:15.238 SUP: VMMR0EntryEx located at ffffffff88d50300, VMMR0EntryFast at ffffffff88d505e0 and VMMR0EntryInt at ffffffff88d4fb30
00:00:15.256 Failed to open the host network interface vbox0
00:00:15.256 ERROR [COM]: aRC=NS_ERROR_FAILURE (0x80004005)
aIID={d5a1cbda-f5d7-4824-9afe-d640c94c7dcf} aComponent={Console} aText={Failed
to open the host network interface vbox0} aWarning=false, preserve=false
00:00:15.257 ERROR [COM]: aRC=NS_ERROR_FAILURE (0x80004005)
aIID={d5a1cbda-f5d7-4824-9afe-d640c94c7dcf} aComponent={Console} aText={Failed
to initialize Host Interface Networking.
00:00:15.257 VBox status code: -3100 (VERR_HOSTIF_INIT_FAILED)} aWarning=false,
preserve=false
00:00:15.262 Power up failed (vrc=VERR_HOSTIF_INIT_FAILED, hrc=NS_ERROR_FAILURE
(0X80004005))
00:00:16.862 VRDP: TCP server closed.

andrex is a member of the group vboxusers, which has read/write permission on /dev/net/tun:

$ ll /dev/net
total 0
crw-rw---- 1 root vboxusers 10, 200 2008-06-15 14:52 tun

A few other data points:

• I tried chmod 0666 /dev/net/tun, but it didn't help.

• root can run this VM, but no other users can AFAICT. So it sure seems like a permission problem, but permissions on interfaces and bridges are hard to debug since they apparently only live in kernel memory. syslog and kern.log provide no useful information.

• I applied the patch described in ​http://www.virtualbox.org/ticket/1714, and that does solve one problem, but /etc/init.d/vboxnet start works correctly now and the problem still isn't resolved.

• This VM used to work fine with the same configuration. I upgraded my kernel a few weeks ago, and probably upgraded some system tools around the same time, and now I can't get past this problem.

Any help would be much appreciated, as I'm currently dead in the water with this VM. NAT networking isn't an option because it doesn't allow me to read Samba shares.

Thanks, Andrew.