Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751900AbdH3MYS (ORCPT ); Wed, 30 Aug 2017 08:24:18 -0400 Received: from mga06.intel.com ([134.134.136.31]:21550 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751332AbdH3MYP (ORCPT ); Wed, 30 Aug 2017 08:24:15 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.41,448,1498546800"; d="scan'208";a="895512284" From: Elena Reshetova To: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, peterz@infradead.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk, tj@kernel.org, mingo@redhat.com, hannes@cmpxchg.org, lizefan@huawei.com, acme@kernel.org, alexander.shishkin@linux.intel.com, eparis@redhat.com, akpm@linux-foundation.org, arnd@arndb.de, luto@kernel.org, keescook@chromium.org, tglx@linutronix.de, dvhart@infradead.org, ebiederm@xmission.com, Elena Reshetova Subject: [PATCH 15/15] kcov: convert kcov.refcount to refcount_t Date: Wed, 30 Aug 2017 15:22:53 +0300 Message-Id: <1504095773-22895-16-git-send-email-elena.reshetova@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1504095773-22895-1-git-send-email-elena.reshetova@intel.com> References: <1504095773-22895-1-git-send-email-elena.reshetova@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2276 Lines: 72 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 kcov.refcount 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 --- kernel/kcov.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/kcov.c b/kernel/kcov.c index cd77199..a6c7df3 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -19,6 +19,7 @@ #include #include #include +#include #include /* @@ -35,7 +36,7 @@ struct kcov { * - opened file descriptor * - task with enabled coverage (we can't unwire it from another task) */ - atomic_t refcount; + refcount_t refcount; /* The lock protects mode, size, area and t. */ spinlock_t lock; enum kcov_mode mode; @@ -94,12 +95,12 @@ EXPORT_SYMBOL(__sanitizer_cov_trace_pc); static void kcov_get(struct kcov *kcov) { - atomic_inc(&kcov->refcount); + refcount_inc(&kcov->refcount); } static void kcov_put(struct kcov *kcov) { - if (atomic_dec_and_test(&kcov->refcount)) { + if (refcount_dec_and_test(&kcov->refcount)) { vfree(kcov->area); kfree(kcov); } @@ -175,7 +176,7 @@ static int kcov_open(struct inode *inode, struct file *filep) kcov = kzalloc(sizeof(*kcov), GFP_KERNEL); if (!kcov) return -ENOMEM; - atomic_set(&kcov->refcount, 1); + refcount_set(&kcov->refcount, 1); spin_lock_init(&kcov->lock); filep->private_data = kcov; return nonseekable_open(inode, filep); -- 2.7.4