From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8B4CC43387 for ; Fri, 18 Jan 2019 12:27:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 91CF32087E for ; Fri, 18 Jan 2019 12:27:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727643AbfARM1x (ORCPT ); Fri, 18 Jan 2019 07:27:53 -0500 Received: from mga05.intel.com ([192.55.52.43]:2175 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727115AbfARM1u (ORCPT ); Fri, 18 Jan 2019 07:27:50 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Jan 2019 04:27:50 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,491,1539673200"; d="scan'208";a="268136110" Received: from elena-thinkpad-x230.fi.intel.com ([10.237.68.34]) by orsmga004.jf.intel.com with ESMTP; 18 Jan 2019 04:27:47 -0800 From: Elena Reshetova To: mingo@redhat.com Cc: peterz@infradead.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, keescook@chromium.org, tglx@linutronix.de, Elena Reshetova Subject: [PATCH 2/5] sched: convert signal_struct.sigcnt to refcount_t Date: Fri, 18 Jan 2019 14:27:27 +0200 Message-Id: <1547814450-18902-3-git-send-email-elena.reshetova@intel.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1547814450-18902-1-git-send-email-elena.reshetova@intel.com> References: <1547814450-18902-1-git-send-email-elena.reshetova@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk 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 signal_struct.sigcnt is used as pure reference counter. Convert it to refcount_t and fix up the operations. **Important note for maintainers: Some functions from refcount_t API defined in lib/refcount.c have different memory ordering guarantees than their atomic counterparts. The full comparison can be seen in https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon in state to be merged to the documentation tree. Normally the differences should not matter since refcount_t provides enough guarantees to satisfy the refcounting use cases, but in some rare cases it might matter. Please double check that you don't have some undocumented memory guarantees for this variable usage. For the signal_struct.sigcnt it might make a difference in following places: - put_signal_struct(): decrement in refcount_dec_and_test() only provides RELEASE ordering and control dependency on success vs. fully ordered atomic counterpart Suggested-by: Kees Cook Reviewed-by: David Windsor Reviewed-by: Hans Liljestrand Signed-off-by: Elena Reshetova --- include/linux/sched/signal.h | 2 +- init/init_task.c | 2 +- kernel/fork.c | 6 +++--- 3 files changed, 5 insertions(+), 5 deletions(-) diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index 2a65721..38a0f07 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -83,7 +83,7 @@ struct multiprocess_signals { * the locking of signal_struct. */ struct signal_struct { - atomic_t sigcnt; + refcount_t sigcnt; atomic_t live; int nr_threads; struct list_head thread_head; diff --git a/init/init_task.c b/init/init_task.c index 26131e7..756be60 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -45,7 +45,7 @@ static struct signal_struct init_signals = { }; static struct sighand_struct init_sighand = { - .count = ATOMIC_INIT(1), + .count = REFCOUNT_INIT(1), .action = { { { .sa_handler = SIG_DFL, } }, }, .siglock = __SPIN_LOCK_UNLOCKED(init_sighand.siglock), .signalfd_wqh = __WAIT_QUEUE_HEAD_INITIALIZER(init_sighand.signalfd_wqh), diff --git a/kernel/fork.c b/kernel/fork.c index 71b4757..504324c 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -709,7 +709,7 @@ static inline void free_signal_struct(struct signal_struct *sig) static inline void put_signal_struct(struct signal_struct *sig) { - if (atomic_dec_and_test(&sig->sigcnt)) + if (refcount_dec_and_test(&sig->sigcnt)) free_signal_struct(sig); } @@ -1527,7 +1527,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk) sig->nr_threads = 1; atomic_set(&sig->live, 1); - atomic_set(&sig->sigcnt, 1); + refcount_set(&sig->sigcnt, 1); /* list_add(thread_node, thread_head) without INIT_LIST_HEAD() */ sig->thread_head = (struct list_head)LIST_HEAD_INIT(tsk->thread_node); @@ -2082,7 +2082,7 @@ static __latent_entropy struct task_struct *copy_process( } else { current->signal->nr_threads++; atomic_inc(¤t->signal->live); - atomic_inc(¤t->signal->sigcnt); + refcount_inc(¤t->signal->sigcnt); task_join_group_stop(p); list_add_tail_rcu(&p->thread_group, &p->group_leader->thread_group); -- 2.7.4