device_cgroup: use css_has_online_children() instead of has_children()

devcgroup_update_access() wants to know whether there are child
cgroups which are online and visible to userland and has_children()
may return false positive.  Replace it with css_has_online_children().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Li Zefan <lizefan@huawei.com>

1 files changed, 2 insertions, 17 deletions

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 084c8e417564..d9d69e6930ed 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -587,21 +587,6 @@ static int propagate_exception(struct dev_cgroup *devcg_root,
         return rc;
 }
 
-static inline bool has_children(struct dev_cgroup *devcgroup)
-{
-        bool ret;
-
-        /*
-         * FIXME: There may be lingering offline csses and this function
-         * may return %true when there isn't any userland-visible child
-         * which is incorrect for our purposes.
-         */
-        rcu_read_lock();
-        ret = css_next_child(NULL, &devcgroup->css);
-        rcu_read_unlock();
-        return ret;
-}
-
 /*
  * Modify the exception list using allow/deny rules.
  * CAP_SYS_ADMIN is needed for this.  It's at least separate from CAP_MKNOD
@@ -634,7 +619,7 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
         case 'a':
                 switch (filetype) {
                 case DEVCG_ALLOW:
-                        if (has_children(devcgroup))
+                        if (css_has_online_children(&devcgroup->css))
                                 return -EINVAL;
 
                         if (!may_allow_all(parent))
@@ -650,7 +635,7 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
                                 return rc;
                         break;
                 case DEVCG_DENY:
-                        if (has_children(devcgroup))
+                        if (css_has_online_children(&devcgroup->css))
                                 return -EINVAL;
 
                         dev_exception_clean(devcgroup);