[Xen-devel] [PATCH 09/29] drivers, md: convert table_device.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.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 9f37d7f..cba91c3 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -21,6 +21,7 @@
 #include <linux/delay.h>
 #include <linux/wait.h>
 #include <linux/pr.h>
+#include <linux/refcount.h>
 
 #define DM_MSG_PREFIX "core"
 
@@ -96,7 +97,7 @@ struct dm_md_mempools {
 
 struct table_device {
        struct list_head list;
-       atomic_t count;
+       refcount_t count;
        struct dm_dev dm_dev;
 };
 
@@ -680,10 +681,11 @@ int dm_get_table_device(struct mapped_device *md, dev_t 
dev, fmode_t mode,
 
                format_dev_t(td->dm_dev.name, dev);
 
-               atomic_set(&td->count, 0);
+               refcount_set(&td->count, 1);
                list_add(&td->list, &md->table_devices);
+       } else {
+               refcount_inc(&td->count);
        }
-       atomic_inc(&td->count);
        mutex_unlock(&md->table_devices_lock);
 
        *result = &td->dm_dev;
@@ -696,7 +698,7 @@ void dm_put_table_device(struct mapped_device *md, struct 
dm_dev *d)
        struct table_device *td = container_of(d, struct table_device, dm_dev);
 
        mutex_lock(&md->table_devices_lock);
-       if (atomic_dec_and_test(&td->count)) {
+       if (refcount_dec_and_test(&td->count)) {
                close_table_device(td, md);
                list_del(&td->list);
                kfree(td);
@@ -713,7 +715,7 @@ static void free_table_devices(struct list_head *devices)
                struct table_device *td = list_entry(tmp, struct table_device, 
list);
 
                DMWARN("dm_destroy: %s still exists with %d references",
-                      td->dm_dev.name, atomic_read(&td->count));
+                      td->dm_dev.name, refcount_read(&td->count));
                kfree(td);
        }
 }
-- 
2.7.4


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