[Xen-devel] [PATCH 08/29] drivers, md: convert mddev.active from atomic_t to refcount_t

[Elena Reshetova <elena.reshetova@xxxxxxxxx>]

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
 drivers/md/md.c | 6 +++---
 drivers/md/md.h | 3 ++-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 985374f..94c8ebf 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -449,7 +449,7 @@ EXPORT_SYMBOL(md_unplug);
 
 static inline struct mddev *mddev_get(struct mddev *mddev)
 {
-       atomic_inc(&mddev->active);
+       refcount_inc(&mddev->active);
        return mddev;
 }
 
@@ -459,7 +459,7 @@ static void mddev_put(struct mddev *mddev)
 {
        struct bio_set *bs = NULL;
 
-       if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
+       if (!refcount_dec_and_lock(&mddev->active, &all_mddevs_lock))
                return;
        if (!mddev->raid_disks && list_empty(&mddev->disks) &&
            mddev->ctime == 0 && !mddev->hold_active) {
@@ -495,7 +495,7 @@ void mddev_init(struct mddev *mddev)
        INIT_LIST_HEAD(&mddev->all_mddevs);
        setup_timer(&mddev->safemode_timer, md_safemode_timeout,
                    (unsigned long) mddev);
-       atomic_set(&mddev->active, 1);
+       refcount_set(&mddev->active, 1);
        atomic_set(&mddev->openers, 0);
        atomic_set(&mddev->active_io, 0);
        spin_lock_init(&mddev->lock);
diff --git a/drivers/md/md.h b/drivers/md/md.h
index b8859cb..4811663 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -22,6 +22,7 @@
 #include <linux/list.h>
 #include <linux/mm.h>
 #include <linux/mutex.h>
+#include <linux/refcount.h>
 #include <linux/timer.h>
 #include <linux/wait.h>
 #include <linux/workqueue.h>
@@ -360,7 +361,7 @@ struct mddev {
         */
        struct mutex                    open_mutex;
        struct mutex                    reconfig_mutex;
-       atomic_t                        active;         /* general refcount */
+       refcount_t                      active;         /* general refcount */
        atomic_t                        openers;        /* number of active 
opens */
 
        int                             changed;        /* True if we might 
need to
-- 
2.7.4


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