Comment 4 for bug 247677

andreas@sturm:~$ grep tun /etc/group
tun:x:1002:andreas

andreas@sturm:~$ groups | grep tun
tun

andreas@sturm:~$ ls -l /dev/net/tun
crw------- 1 root root 10, 200 2008-04-29 23:05 /dev/net/tun
andreas@sturm:~$ sudo chown :tun /dev/net/tun
[sudo] password for andreas:
andreas@sturm:~$ ls -l /dev/net/tun
crw------- 1 root tun 10, 200 2008-04-29 23:05 /dev/net/tun

and with read and write access for group tun:
crw-rw---- 1 root tun 10, 200 2008-04-29 23:05 /dev/net/tun

The same problem:

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/engine.py", line 480, in run_domain
    vm.startup()
  File "/usr/share/virt-manager/virtManager/domain.py", line 379, in startup
    self.vm.create()
  File "/usr/lib/python2.5/site-packages/libvirt.py", line 240, in create
    if ret == -1: raise libvirtError ('virDomainCreate() failed', dom=self)
libvirtError: virDomainCreate() failed Failed to add tap interface 'vnet%d' to bridge 'br0' : Operation not permitted