[PATCH 2/4] dm cache: convert dm_cache_metadata.ref_count from atomic_t to refcount_t
From: Elena Reshetova <elena.reshetova@intel.com>
Date: 2017-10-20 07:38:45
Also in:
dm-devel, linux-bcache, lkml
Subsystem:
device-mapper (lvm), the rest · Maintainers:
Alasdair Kergon, Mike Snitzer, Mikulas Patocka, Benjamin Marzinski, Linus Torvalds
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 dm_cache_metadata.ref_count is used as pure reference counter. Convert it to refcount_t and fix up the operations. Suggested-by: Kees Cook <redacted> Reviewed-by: David Windsor <redacted> Reviewed-by: Hans Liljestrand <redacted> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com> --- 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 4a4e9c7..0d72124 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> /*----------------------------------------------------------------*/
@@ -100,7 +101,7 @@ struct cache_disk_superblock { } __packed; struct dm_cache_metadata { - atomic_t ref_count; + refcount_t ref_count; struct list_head list; unsigned version;
@@ -753,7 +754,7 @@ 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;
@@ -791,7 +792,7 @@ 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; }
@@ -862,7 +863,7 @@ 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