On 07.10.2014 17:19, Eric Blake wrote:
On 10/07/2014 08:53 AM, Michal Privoznik wrote:
https://bugzilla.redhat.com/show_bug.cgi?id=1147057
The code for relabelling the TAP FD is there due to a race. When libvirt creates a /dev/tapN device it's labeled as 'system_u:object_r:device_t:s0' by default. Later, when udev/systemd reacts to this device, it's relabelled to the expected label 'system_u:object_r:tun_tap_device_t:s0'. Hence, we have a code that relabels the device, to cut the race down. For more info see ae368ebfcc4.
But the problem is, the relabel function is called on all TUN/TAP devices. Yes, on /dev/net/tun too. This is however a special kind of device - other processes uses it too. We shouldn't touch it's label then.
Ideally, there would an API in SELinux that would label just the passed FD and not the underlying path. That way, we wouldn't need to care as we would be not labeling /dev/net/tun but the FD passed to the domain. Unfortunately, there's no such API so we have to workaround until then.
+ + if (!STRPREFIX(fd_path, "/dev/tap")) {
Should this be "/dev/tap.", since...
+ VIR_DEBUG("fd=%d points to %s not setting SELinux label", + fd, fd_path); + rc = 0; + goto cleanup; + } + if (getContext(mgr, "/dev/tap.*", buf.st_mode, &fcon) < 0) {
...you require a '.' in the context lookup? Without the '.' in the filter, you would let the (unlikely) name '/dev/tapX' get through.
ACK with that tweaked.
In fact, /dev/tapX is what is created. getContext should be using it too as it accepts shell expendable names, not regular expressions. I'm adjusting getContext's argument too. Michal