Commit 201e72ac authored by Tejun Heo's avatar Tejun Heo

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: default avatarTejun Heo <>
Acked-by: default avatarSerge E. Hallyn <>
Cc: Aristeu Rozanski <>
Cc: Li Zefan <>
parent 64e10477
......@@ -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) {
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))
if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))
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