security: dac: also label listen UNIX sockets

We switched to opening mode='bind' sockets ourselves:
commit 30fb2276
    qemu: support passing pre-opened UNIX socket listen FD
in v4.5.0-rc1~251

Then fixed qemuBuildChrChardevStr to change libvirtd's label
while creating the socket:
commit b0c6300f
    qemu: ensure FDs passed to QEMU for chardevs have correct SELinux labels
v4.5.0-rc1~52

Also add labeling of these sockets to the DAC driver.
Instead of duplicating the logic which decides whether libvirt should
pre-create the socket, assume an existing path meaning that it was created
by libvirt.

https://bugzilla.redhat.com/show_bug.cgi?id=1633389Signed-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

src/security/security_dac.c

@@ -1308,7 +1308,12 @@ virSecurityDACSetChardevLabel(virSecurityManagerPtr mgr,
         break;
 
     case VIR_DOMAIN_CHR_TYPE_UNIX:
-        if (!dev_source->data.nix.listen) {
+        if (!dev_source->data.nix.listen ||
+            (dev_source->data.nix.path &&
+             virFileExists(dev_source->data.nix.path))) {
+            /* Also label mode='bind' sockets if they exist,
+             * e.g. because they were created by libvirt
+             * and passed via FD */
             if (virSecurityDACSetOwnership(mgr, NULL,
                                            dev_source->data.nix.path,
                                            user, group) < 0)