vmur: convert urdev.ref_count from atomic_t to refcount_t
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 urdev.ref_count 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: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/drivers/s390/char/vmur.c b/drivers/s390/char/vmur.c
index a50cf93..fa90ef0 100644
--- a/drivers/s390/char/vmur.c
+++ b/drivers/s390/char/vmur.c
@@ -110,7 +110,7 @@ static struct urdev *urdev_alloc(struct ccw_device *cdev)
mutex_init(&urd->io_mutex);
init_waitqueue_head(&urd->wait);
spin_lock_init(&urd->open_lock);
- atomic_set(&urd->ref_count, 1);
+ refcount_set(&urd->ref_count, 1);
urd->cdev = cdev;
get_device(&cdev->dev);
return urd;
@@ -126,7 +126,7 @@ static void urdev_free(struct urdev *urd)
static void urdev_get(struct urdev *urd)
{
- atomic_inc(&urd->ref_count);
+ refcount_inc(&urd->ref_count);
}
static struct urdev *urdev_get_from_cdev(struct ccw_device *cdev)
@@ -159,7 +159,7 @@ static struct urdev *urdev_get_from_devno(u16 devno)
static void urdev_put(struct urdev *urd)
{
- if (atomic_dec_and_test(&urd->ref_count))
+ if (refcount_dec_and_test(&urd->ref_count))
urdev_free(urd);
}
@@ -945,7 +945,7 @@ static int ur_set_offline_force(struct ccw_device *cdev, int force)
rc = -EBUSY;
goto fail_urdev_put;
}
- if (!force && (atomic_read(&urd->ref_count) > 2)) {
+ if (!force && (refcount_read(&urd->ref_count) > 2)) {
/* There is still a user of urd (e.g. ur_open) */
TRACE("ur_set_offline: BUSY\n");
rc = -EBUSY;