device_cgroup: add "deny_all" in dev_cgroup structure

deny_all will determine if the default policy is to deny all device access
unless for the ones in the exception list.

This variable will be used in the next patches to convert device_cgroup
internally into a default policy + rules.

Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: James Morris <jmorris@namei.org>
Cc: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

security/device_cgroup.c

@@ -42,6 +42,7 @@ struct dev_whitelist_item {
 struct dev_cgroup {
 	struct cgroup_subsys_state css;
 	struct list_head whitelist;
+	bool deny_all;
 };
 
 static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
@@ -178,12 +179,14 @@ static struct cgroup_subsys_state *devcgroup_create(struct cgroup *cgroup)
 		wh->minor = wh->major = ~0;
 		wh->type = DEV_ALL;
 		wh->access = ACC_MASK;
+		dev_cgroup->deny_all = false;
 		list_add(&wh->list, &dev_cgroup->whitelist);
 	} else {
 		parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
 		mutex_lock(&devcgroup_mutex);
 		ret = dev_whitelist_copy(&dev_cgroup->whitelist,
 				&parent_dev_cgroup->whitelist);
+		dev_cgroup->deny_all = parent_dev_cgroup->deny_all;
 		mutex_unlock(&devcgroup_mutex);
 		if (ret) {
 			kfree(dev_cgroup);
@@ -409,9 +412,11 @@ handle:
 	case DEVCG_ALLOW:
 		if (!parent_has_perm(devcgroup, &wh))
 			return -EPERM;
+		devcgroup->deny_all = false;
 		return dev_whitelist_add(devcgroup, &wh);
 	case DEVCG_DENY:
 		dev_whitelist_rm(devcgroup, &wh);
+		devcgroup->deny_all = true;
 		break;
 	default:
 		return -EINVAL;