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dm cache: convert dm_cache_metadata.ref_count from atomic_t to refcount_t

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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 <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Elena Reshetova 2017-10-20 10:37:37 +03:00 committed by Mike Snitzer
parent b0b4d7c675
commit 6bdd079610
1 changed files with 5 additions and 4 deletions
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9
drivers/md/dm-cache-metadata.c
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@ -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);