kernel: convert css_set.refcount from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

3 files changed, 8 insertions, 7 deletions

diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 9203bfb..4567f12 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -5,6 +5,7 @@
 #include <linux/kernfs.h>
 #include <linux/workqueue.h>
 #include <linux/list.h>
+#include <linux/refcount.h>
 
 /*
  * A cgroup can be associated with multiple css_sets as different tasks may
@@ -134,7 +135,7 @@ static inline void put_css_set(struct css_set *cset)
 	 * can see it. Similar to atomic_dec_and_lock(), but for an
 	 * rwlock
 	 */
-	if (atomic_add_unless(&cset->refcount, -1, 1))
+	if (refcount_dec_not_one(&cset->refcount))
 		return;
 
 	spin_lock_irqsave(&css_set_lock, flags);
@@ -147,7 +148,7 @@ static inline void put_css_set(struct css_set *cset)
  */
 static inline void get_css_set(struct css_set *cset)
 {
-	atomic_inc(&cset->refcount);
+	refcount_inc(&cset->refcount);
 }
 
 bool cgroup_ssid_enabled(int ssid);
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 56eba9c..c4a68c4 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -346,7 +346,7 @@ static int cgroup_task_count(const struct cgroup *cgrp)
 
 	spin_lock_irq(&css_set_lock);
 	list_for_each_entry(link, &cgrp->cset_links, cset_link)
-		count += atomic_read(&link->cset->refcount);
+		count += refcount_read(&link->cset->refcount);
 	spin_unlock_irq(&css_set_lock);
 	return count;
 }
@@ -1286,7 +1286,7 @@ static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css,
 	u64 count;
 
 	rcu_read_lock();
-	count = atomic_read(&task_css_set(current)->refcount);
+	count = refcount_read(&task_css_set(current)->refcount);
 	rcu_read_unlock();
 	return count;
 }
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 8ee7868..b1cc1c3 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -554,7 +554,7 @@ EXPORT_SYMBOL_GPL(of_css);
  * haven't been created.
  */
 struct css_set init_css_set = {
-	.refcount		= ATOMIC_INIT(1),
+	.refcount		= REFCOUNT_INIT(1),
 	.tasks			= LIST_HEAD_INIT(init_css_set.tasks),
 	.mg_tasks		= LIST_HEAD_INIT(init_css_set.mg_tasks),
 	.task_iters		= LIST_HEAD_INIT(init_css_set.task_iters),
@@ -724,7 +724,7 @@ void put_css_set_locked(struct css_set *cset)
 
 	lockdep_assert_held(&css_set_lock);
 
-	if (!atomic_dec_and_test(&cset->refcount))
+	if (!refcount_dec_and_test(&cset->refcount))
 		return;
 
 	/* This css_set is dead. unlink it and release cgroup and css refs */
@@ -977,7 +977,7 @@ static struct css_set *find_css_set(struct css_set *old_cset,
 		return NULL;
 	}
 
-	atomic_set(&cset->refcount, 1);
+	refcount_set(&cset->refcount, 1);
 	INIT_LIST_HEAD(&cset->tasks);
 	INIT_LIST_HEAD(&cset->mg_tasks);
 	INIT_LIST_HEAD(&cset->task_iters);