devcgroup: fix race against rmdir()
During the use of a dev_cgroup, we should guarantee the corresponding
cgroup won't be deleted (i.e. via rmdir). This can be done through
css_get(&dev_cgroup->css), but here we can just get and use the dev_cgroup
under rcu_read_lock.
And also remove checking NULL dev_cgroup, it won't be NULL since a task
always belongs to a cgroup.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 7bd296c..46f2397 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -508,12 +508,11 @@
return 0;
if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
return 0;
- dev_cgroup = css_to_devcgroup(task_subsys_state(current,
- devices_subsys_id));
- if (!dev_cgroup)
- return 0;
rcu_read_lock();
+
+ dev_cgroup = task_devcgroup(current);
+
list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
if (wh->type & DEV_ALL)
goto acc_check;
@@ -533,6 +532,7 @@
rcu_read_unlock();
return 0;
}
+
rcu_read_unlock();
return -EPERM;
@@ -543,12 +543,10 @@
struct dev_cgroup *dev_cgroup;
struct dev_whitelist_item *wh;
- dev_cgroup = css_to_devcgroup(task_subsys_state(current,
- devices_subsys_id));
- if (!dev_cgroup)
- return 0;
-
rcu_read_lock();
+
+ dev_cgroup = task_devcgroup(current);
+
list_for_each_entry(wh, &dev_cgroup->whitelist, list) {
if (wh->type & DEV_ALL)
goto acc_check;
@@ -566,6 +564,8 @@
rcu_read_unlock();
return 0;
}
+
rcu_read_unlock();
+
return -EPERM;
}