device_cgroup: fix RCU usage

dev_cgroup->exceptions is protected with devcgroup_mutex for writes
and RCU for reads; however, RCU usage isn't correct.

* dev_exception_clean() doesn't use RCU variant of list_del() and
  kfree().  The function can race with may_access() and may_access()
  may end up dereferencing already freed memory.  Use list_del_rcu()
  and kfree_rcu() instead.

* may_access() may be called only with RCU read locked but doesn't use
  RCU safe traversal over ->exceptions.  Use list_for_each_entry_rcu().

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

diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 96d87eab166058a75bad402dc71c97a89994e1f9..b08d20c66c2e17e0fa8333984df8eb4a82595e0b 100644 (file)
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -164,8 +164,8 @@ static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
        struct dev_exception_item *ex, *tmp;
 
        list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
-               list_del(&ex->list);
-               kfree(ex);
+               list_del_rcu(&ex->list);
+               kfree_rcu(ex, rcu);
        }
 }
 
@@ -298,7 +298,7 @@ static int may_access(struct dev_cgroup *dev_cgroup,
        struct dev_exception_item *ex;
        bool match = false;
 
-       list_for_each_entry(ex, &dev_cgroup->exceptions, list) {
+       list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) {
                if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
                        continue;
                if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))