From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga04.intel.com ([192.55.52.120]:17199 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752092AbdJTKcB (ORCPT ); Fri, 20 Oct 2017 06:32:01 -0400 From: Elena Reshetova To: jack@suse.cz Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, amir73il@gmail.com, peterz@infradead.org, keescook@chromium.org, Elena Reshetova Subject: [PATCH 1/2] fsnotify: convert fsnotify_group.refcnt from atomic_t to refcount_t Date: Fri, 20 Oct 2017 13:26:01 +0300 Message-Id: <1508495162-32339-1-git-send-email-elena.reshetova@intel.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 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 fsnotify_group.refcnt 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 --- fs/notify/group.c | 6 +++--- include/linux/fsnotify_backend.h | 3 ++- 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/fs/notify/group.c b/fs/notify/group.c index 3235753..b7a4b6a 100644 --- a/fs/notify/group.c +++ b/fs/notify/group.c @@ -107,7 +107,7 @@ void fsnotify_destroy_group(struct fsnotify_group *group) */ void fsnotify_get_group(struct fsnotify_group *group) { - atomic_inc(&group->refcnt); + refcount_inc(&group->refcnt); } /* @@ -115,7 +115,7 @@ void fsnotify_get_group(struct fsnotify_group *group) */ void fsnotify_put_group(struct fsnotify_group *group) { - if (atomic_dec_and_test(&group->refcnt)) + if (refcount_dec_and_test(&group->refcnt)) fsnotify_final_destroy_group(group); } @@ -131,7 +131,7 @@ struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops) return ERR_PTR(-ENOMEM); /* set to 0 when there a no external references to this group */ - atomic_set(&group->refcnt, 1); + refcount_set(&group->refcnt, 1); atomic_set(&group->num_marks, 0); atomic_set(&group->user_waits, 0); diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h index c6c6931..20a57ba 100644 --- a/include/linux/fsnotify_backend.h +++ b/include/linux/fsnotify_backend.h @@ -17,6 +17,7 @@ #include #include #include +#include /* * IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily @@ -135,7 +136,7 @@ struct fsnotify_group { * inotify_init() and the refcnt will hit 0 only when that fd has been * closed. */ - atomic_t refcnt; /* things with interest in this group */ + refcount_t refcnt; /* things with interest in this group */ const struct fsnotify_ops *ops; /* how this group handles things */ -- 2.7.4