On Wed, Aug 18, 2021 at 09:00:52AM -0400, Laine Stump wrote: > On 8/18/21 4:21 AM, Michal Prívozník wrote: > > On 8/18/21 12:31 AM, Jim Fehlig wrote: > > > On 8/17/21 12:11 PM, Jim Fehlig wrote: > > > > On 8/17/21 4:13 AM, Michal Prívozník wrote: > > > > > On 8/13/21 11:36 PM, Jim Fehlig wrote: > > > > > > Attaching a newly created vhostuser port to a VM fails due to an > > > > > > apparmor denial > > > > > > > > > > > > internal error: unable to execute QEMU command 'chardev-add': Failed > > > > > > to bind socket to /run/openvswitch/vhu838c4d29-c9: Permission denied > > > > > > > > > > > > In the case of a net device type VIR_DOMAIN_NET_TYPE_VHOSTUSER, the > > > > > > underlying chardev is not labeled in qemuDomainAttachNetDevice prior > > > > > > to calling qemuMonitorAttachCharDev. Label the chardev before calling > > > > > > qemuMonitorAttachCharDev, and restore the label when removing the > > > > > > net device. > > > > > > > > > > > > Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx> > > > > > > --- > > > > > > src/qemu/qemu_hotplug.c | 9 +++++++++ > > > > > > 1 file changed, 9 insertions(+) > > > > > > > > > > > > diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c > > > > > > index c00e8a7852..42e7997112 100644 > > > > > > --- a/src/qemu/qemu_hotplug.c > > > > > > +++ b/src/qemu/qemu_hotplug.c > > > > > > @@ -1467,6 +1467,11 @@ qemuDomainAttachNetDevice(virQEMUDriver *driver, > > > > > > } > > > > > > if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { > > > > > > + virDomainChrDef chr = { .source = net->data.vhostuser }; > > > > > > + > > > > > > + if (qemuSecuritySetChardevLabel(driver, vm, &chr) < 0) > > > > > > + goto cleanup; > > > > > > + > > > > > > if (qemuMonitorAttachCharDev(priv->mon, charDevAlias, > > > > > > net->data.vhostuser) < 0) { > > > > > > ignore_value(qemuDomainObjExitMonitor(driver, vm)); > > > > > > virDomainAuditNet(vm, NULL, net, "attach", false); > > > > > > @@ -4692,6 +4697,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, > > > > > > } > > > > > > if (actualType == VIR_DOMAIN_NET_TYPE_VHOSTUSER) { > > > > > > + virDomainChrDef chr = { .source = net->data.vhostuser }; > > > > > > + > > > > > > /* vhostuser has a chardev too */ > > > > > > if (qemuMonitorDetachCharDev(priv->mon, charDevAlias) < 0) { > > > > > > /* well, this is a messy situation. Guest visible PCI > > > > > > device has > > > > > > @@ -4699,6 +4706,8 @@ qemuDomainRemoveNetDevice(virQEMUDriver *driver, > > > > > > * to just ignore the error and carry on. > > > > > > */ > > > > > > } > > > > > > + if (qemuSecurityRestoreChardevLabel(driver, vm, &chr) < 0) > > > > > > + VIR_WARN("Unable to restore security label on vhostuser > > > > > > char device"); > > > > > > } else if (actualType == VIR_DOMAIN_NET_TYPE_VDPA) { > > > > > > int vdpafdset = -1; > > > > > > g_autoptr(qemuMonitorFdsets) fdsets = NULL; > > > > > > > > > > > > > > > > What an interesting bug. Previously we assumed that the UNIX socket is > > > > > created with broad enough permissions so that QEMU can connect to it. I > > > > > mean, when a VM is starting up nor DAC nor SELinux drivers care about > > > > > VHOSTUSER. It's AppArmor driver that cares. And it makes sense. > > > > > But, what's problematic here is that upon attach the socket perms will > > > > > be changed (because both DAC and SELinux drivers implement > > > > > domainSetSecurityChardevLabel callback). And since sockets can't have > > > > > XATTRs libvirt won't remember its original labels and thus subsequent > > > > > restore changes owner to root:root. > > > > > > > > How are existing chardevs with socket backends handled? It seems they > > > > would suffer the same problem when restoring the labels. The DAC and > > > > selinux callbacks seem to avoid labeling for "server" sockets > > > > > > > > https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_dac.c#L1534 > > > > > > > > https://gitlab.com/libvirt/libvirt/-/blob/master/src/security/security_selinux.c#L2544 > > > > > > > > Yeah, you're right. But I view chardevs as runtime, fire and go things. > > I mean, you start a VM with a chardev, say an UNIX socket and its > > lifetime is identical to the VM lifetime. vhostuser on the other hand is > > handled by a third party daemon (typically OVS) and thus UNIX socket > > lifetime is different to VM lifetime. IOW, I worry that if we changed > > the UNIX socket label we might be preventing other VMs from connecting > > to it. > > > > And I don't even know if a single socket can be shared between two VMs. > > For instance, if OVS created an UNIX socket whether I can attach > > vhostuser interface to one domain and then to the other. Because if I > > could, then we should not change labels. > > > > Perhaps Laine can shed more light here. > > Sorry, I really know nothing about this topic. Who would be the proper > person at the next level down to ask? Michael, do you know? hmm... Maxime? > > > > > I do understand that apparmor needs to add an entry to the VM's profile, > > but I worry that DAC and SELinux might screw things up. > > > > > > > > > > > So I think we should address this inconsistency in behavior. But I don't > > > > > know how :-( > > > > > > > > My first attempt at fixing this introduced > > > > domain{Set,Restore}SecurityNetdevLabel to the security driver, but it > > > > seemed like overkill after I discovered virDomainChrSourceDef embedded > > > > in the virDomainNetDef structure. I can revisit that approach if it > > > > sounds more promising. > > > > I think it does sound more promising given my assumption above is > > correct. This way we can have only AppArmor driver implement the > > callback leaving us with consistent behavior. > > > > Michal > >