From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752348AbdJTHip (ORCPT ); Fri, 20 Oct 2017 03:38:45 -0400 Received: from mga01.intel.com ([192.55.52.88]:44912 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751989AbdJTHim (ORCPT ); Fri, 20 Oct 2017 03:38:42 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.43,405,1503385200"; d="scan'208";a="1233064274" From: Elena Reshetova To: dm-devel@redhat.com Cc: linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, kent.overstreet@gmail.com, koverstreet@google.com, ejt@redhat.comg, snitzer@redhat.com, shli@kernel.org, agk@redhat.com, peterz@infradead.org, keescook@chromium.org, Elena Reshetova Subject: [PATCH 2/4] dm cache: convert dm_cache_metadata.ref_count from atomic_t to refcount_t Date: Fri, 20 Oct 2017 10:37:37 +0300 Message-Id: <1508485059-21881-3-git-send-email-elena.reshetova@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1508485059-21881-1-git-send-email-elena.reshetova@intel.com> References: <1508485059-21881-1-git-send-email-elena.reshetova@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Signed-off-by: Elena Reshetova --- 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 +#include /*----------------------------------------------------------------*/ @@ -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