qemu: don't request cgroup ACL access for /dev/net/tun

Since libvirt always passes /dev/net/tun to qemu via fd, we should
never trigger the cases where qemu tries to directly open the
device.  Therefore, it is safer to deny the cgroup device ACL.

* src/qemu/qemu_cgroup.c (defaultDeviceACL): Remove /dev/net/tun.
* src/qemu/qemu.conf (cgroup_device_acl): Reflect this change.

src/qemu/qemu.conf

@@ -182,7 +182,7 @@
 #    "/dev/null", "/dev/full", "/dev/zero",
 #    "/dev/random", "/dev/urandom",
 #    "/dev/ptmx", "/dev/kvm", "/dev/kqemu",
-#    "/dev/rtc", "/dev/hpet", "/dev/net/tun",
+#    "/dev/rtc", "/dev/hpet",
 #]
 
 

src/qemu/qemu_cgroup.c

@@ -37,7 +37,7 @@ static const char *const defaultDeviceACL[] = {
     "/dev/null", "/dev/full", "/dev/zero",
     "/dev/random", "/dev/urandom",
     "/dev/ptmx", "/dev/kvm", "/dev/kqemu",
-    "/dev/rtc", "/dev/hpet", "/dev/net/tun",
+    "/dev/rtc", "/dev/hpet",
     NULL,
 };
 #define DEVICE_PTY_MAJOR 136