atomic_t variables are currently used to implement reference
counters with the following properties:
- counter is initialized to 1 using atomic_set()
- a resource is freed upon counter reaching zero
- once counter reaches zero, its further
increments aren't allowed
- counter schema uses basic atomic operations
(set, inc, inc_not_zero, dec_and_test, etc.)
Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.
The variable cn_callback_entry.refcnt is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: David Windsor <dwindsor@xxxxxxxxx>
Reviewed-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
---
drivers/connector/cn_queue.c | 4 ++--
drivers/connector/connector.c | 2 +-
include/linux/connector.h | 4 ++--
3 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/connector/cn_queue.c b/drivers/connector/cn_queue.c
index 1f8bf05..9c54fdf 100644
--- a/drivers/connector/cn_queue.c
+++ b/drivers/connector/cn_queue.c
@@ -45,7 +45,7 @@ cn_queue_alloc_callback_entry(struct cn_queue_dev *dev, const char *name,
return NULL;
}
- atomic_set(&cbq->refcnt, 1);
+ refcount_set(&cbq->refcnt, 1);
atomic_inc(&dev->refcnt);
cbq->pdev = dev;
@@ -58,7 +58,7 @@ cn_queue_alloc_callback_entry(struct cn_queue_dev *dev, const char *name,
void cn_queue_release_callback(struct cn_callback_entry *cbq)
{
- if (!atomic_dec_and_test(&cbq->refcnt))
+ if (!refcount_dec_and_test(&cbq->refcnt))
return;
atomic_dec(&cbq->pdev->refcnt);
diff --git a/drivers/connector/connector.c b/drivers/connector/connector.c
index 25693b0..8615594b 100644
--- a/drivers/connector/connector.c
+++ b/drivers/connector/connector.c
@@ -157,7 +157,7 @@ static int cn_call_callback(struct sk_buff *skb)
spin_lock_bh(&dev->cbdev->queue_lock);
list_for_each_entry(i, &dev->cbdev->queue_list, callback_entry) {
if (cn_cb_equal(&i->id.id, &msg->id)) {
- atomic_inc(&i->refcnt);
+ refcount_inc(&i->refcnt);
cbq = i;
break;
}
diff --git a/include/linux/connector.h b/include/linux/connector.h
index f8fe863..032102b 100644
--- a/include/linux/connector.h
+++ b/include/linux/connector.h
@@ -22,7 +22,7 @@
#define __CONNECTOR_H
-#include <linux/atomic.h>
+#include <linux/refcount.h>
#include <linux/list.h>
#include <linux/workqueue.h>
@@ -49,7 +49,7 @@ struct cn_callback_id {
struct cn_callback_entry {
struct list_head callback_entry;
- atomic_t refcnt;
+ refcount_t refcnt;
struct cn_queue_dev *pdev;
struct cn_callback_id id;
--
2.7.4
--
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