Commit 201e72ac authored Nov 06, 2012 by 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: 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>

parent 64e10477

security/device_cgroup.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -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))

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