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drivers, connector: convert cn_callback_entry.refcnt from atomic_t to refcount_t

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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@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Elena Reshetova 2017-10-20 10:23:49 +03:00 committed by David S. Miller
parent 709c89b45b
commit e65f7ee39b
3 changed files with 5 additions and 5 deletions
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4
drivers/connector/cn_queue.c
View File

@ -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);

2
drivers/connector/connector.c
View File

@ -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;
}

4
include/linux/connector.h
View File

@ -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;