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 <keesc...@chromium.org> Reviewed-by: David Windsor <dwind...@gmail.com> Reviewed-by: Hans Liljestrand <ishkam...@gmail.com> Signed-off-by: Elena Reshetova <elena.reshet...@intel.com> --- drivers/s390/char/vmur.c | 8 ++++---- drivers/s390/char/vmur.h | 4 +++- 2 files changed, 7 insertions(+), 5 deletions(-) diff --git a/drivers/s390/char/vmur.c b/drivers/s390/char/vmur.c index 04aceb6..ced8151 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); } @@ -946,7 +946,7 @@ 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; diff --git a/drivers/s390/char/vmur.h b/drivers/s390/char/vmur.h index fa320ad..35ea9d1 100644 --- a/drivers/s390/char/vmur.h +++ b/drivers/s390/char/vmur.h @@ -11,6 +11,8 @@ #ifndef _VMUR_H_ #define _VMUR_H_ +#include <linux/refcount.h> + #define DEV_CLASS_UR_I 0x20 /* diag210 unit record input device class */ #define DEV_CLASS_UR_O 0x10 /* diag210 unit record output device class */ /* @@ -69,7 +71,7 @@ struct urdev { size_t reclen; /* Record length for *write* CCWs */ int class; /* VM device class */ int io_request_rc; /* return code from I/O request */ - atomic_t ref_count; /* reference counter */ + refcount_t ref_count; /* reference counter */ wait_queue_head_t wait; /* wait queue to serialize open */ int open_flag; /* "urdev is open" flag */ spinlock_t open_lock; /* serialize critical sections */ -- 2.7.4