[Xen-devel] [PATCH 06/29] drivers, md: convert dm_cache_metadata.ref_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-cache-metadata.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-cache-metadata.c b/drivers/md/dm-cache-metadata.c
index e4c2c1a..6d26e71 100644
--- a/drivers/md/dm-cache-metadata.c
+++ b/drivers/md/dm-cache-metadata.c
@@ -13,6 +13,7 @@
 #include "persistent-data/dm-transaction-manager.h"
 
 #include <linux/device-mapper.h>
+#include <linux/refcount.h>
 
 /*----------------------------------------------------------------*/
 
@@ -102,7 +103,7 @@ struct cache_disk_superblock {
 } __packed;
 
 struct dm_cache_metadata {
-       atomic_t ref_count;
+       refcount_t ref_count;
        struct list_head list;
 
        unsigned version;
@@ -756,7 +757,7 @@ static struct dm_cache_metadata *metadata_open(struct 
block_device *bdev,
        }
 
        cmd->version = metadata_version;
-       atomic_set(&cmd->ref_count, 1);
+       refcount_set(&cmd->ref_count, 1);
        init_rwsem(&cmd->root_lock);
        cmd->bdev = bdev;
        cmd->data_block_size = data_block_size;
@@ -794,7 +795,7 @@ static struct dm_cache_metadata *lookup(struct block_device 
*bdev)
 
        list_for_each_entry(cmd, &table, list)
                if (cmd->bdev == bdev) {
-                       atomic_inc(&cmd->ref_count);
+                       refcount_inc(&cmd->ref_count);
                        return cmd;
                }
 
@@ -865,7 +866,7 @@ struct dm_cache_metadata *dm_cache_metadata_open(struct 
block_device *bdev,
 
 void dm_cache_metadata_close(struct dm_cache_metadata *cmd)
 {
-       if (atomic_dec_and_test(&cmd->ref_count)) {
+       if (refcount_dec_and_test(&cmd->ref_count)) {
                mutex_lock(&table_lock);
                list_del(&cmd->list);
                mutex_unlock(&table_lock);
-- 
2.7.4


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