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vmur: convert urdev.ref_count 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 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>
This commit is contained in:
Elena Reshetova 2017-10-20 10:47:48 +03:00 committed by Martin Schwidefsky
parent 3593eb944c
commit 0462d9921e
2 changed files with 7 additions and 5 deletions
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8
drivers/s390/char/vmur.c
View file

@ -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;

4
drivers/s390/char/vmur.h
View file

@ -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 */