[Xen-devel] [PATCH 07/29] drivers, md: convert dm_dev_internal.count 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/dm-table.c | 6 +++---
 drivers/md/dm.h       | 3 ++-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 3ad16d9..d2e2741 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -416,15 +416,15 @@ int dm_get_device(struct dm_target *ti, const char *path, 
fmode_t mode,
                        return r;
                }
 
-               atomic_set(&dd->count, 0);
+               refcount_set(&dd->count, 1);
                list_add(&dd->list, &t->devices);
 
        } else if (dd->dm_dev->mode != (mode | dd->dm_dev->mode)) {
                r = upgrade_mode(dd, mode, t->md);
                if (r)
                        return r;
+               refcount_inc(&dd->count);
        }
-       atomic_inc(&dd->count);
 
        *result = dd->dm_dev;
        return 0;
@@ -478,7 +478,7 @@ void dm_put_device(struct dm_target *ti, struct dm_dev *d)
                       dm_device_name(ti->table->md), d->name);
                return;
        }
-       if (atomic_dec_and_test(&dd->count)) {
+       if (refcount_dec_and_test(&dd->count)) {
                dm_put_table_device(ti->table->md, d);
                list_del(&dd->list);
                kfree(dd);
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index f298b01..63b8142 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -19,6 +19,7 @@
 #include <linux/hdreg.h>
 #include <linux/completion.h>
 #include <linux/kobject.h>
+#include <linux/refcount.h>
 
 #include "dm-stats.h"
 
@@ -38,7 +39,7 @@
  */
 struct dm_dev_internal {
        struct list_head list;
-       atomic_t count;
+       refcount_t count;
        struct dm_dev *dm_dev;
 };
 
-- 
2.7.4


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