From patchwork Wed Nov 9 06:41:47 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Yu Liao X-Patchwork-Id: 1701611 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@legolas.ozlabs.org Authentication-Results: legolas.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=2620:137:e000::1:20; helo=out1.vger.email; envelope-from=linux-rtc-owner@vger.kernel.org; receiver=) Received: from out1.vger.email (out1.vger.email [IPv6:2620:137:e000::1:20]) by legolas.ozlabs.org (Postfix) with ESMTP id 4N6bH53K1Sz23mN for ; Wed, 9 Nov 2022 17:51:45 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229777AbiKIGvo (ORCPT ); Wed, 9 Nov 2022 01:51:44 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229787AbiKIGvn (ORCPT ); Wed, 9 Nov 2022 01:51:43 -0500 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8BCC818B03; Tue, 8 Nov 2022 22:51:42 -0800 (PST) Received: from dggpeml500023.china.huawei.com (unknown [172.30.72.55]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4N6bCW4ljXzDsJM; Wed, 9 Nov 2022 14:48:39 +0800 (CST) Received: from dggpeml500003.china.huawei.com (7.185.36.200) by dggpeml500023.china.huawei.com (7.185.36.114) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 9 Nov 2022 14:51:40 +0800 Received: from huawei.com (10.175.103.91) by dggpeml500003.china.huawei.com (7.185.36.200) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 9 Nov 2022 14:51:40 +0800 From: Yu Liao To: , CC: , , , Subject: [PATCH v1 2/2] rtc: fix race condition in rtc_set_time() Date: Wed, 9 Nov 2022 14:41:47 +0800 Message-ID: <20221109064147.1836133-3-liaoyu15@huawei.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20221109064147.1836133-1-liaoyu15@huawei.com> References: <20221109064147.1836133-1-liaoyu15@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.175.103.91] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpeml500003.china.huawei.com (7.185.36.200) X-CFilter-Loop: Reflected X-Spam-Status: No, score=-2.2 required=5.0 tests=BAYES_00,HK_RANDOM_ENVFROM, HK_RANDOM_FROM,RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-rtc@vger.kernel.org Commit 7e7c005b4b1f ("rtc: disable uie before setting time and enable after") was introduced to solve problem that rtc_timer_do_work will loop for a while, when setting the time in the future with the uie timer enabled. But reading uie timer state and setting rtc time are not in a critical section, a race condition may occur in rtc_set_time which has two issues: 1) In the above scenario, rtc_timer_do_work may still loop for a while. For example consider the following sequence: CPU0 CPU1 ---- ---- ioctl(RTC_SET_TIME) ioctl(RTC_UIE_ON) uie = rtc->uie_rtctimer.enabled; [ assume uie is 0 ] if (uie) rtc_update_irq_enable(rtc, 0); rtc_update_irq_enable(rtc, 1); [ uie is enabled ] rtc->ops->set_time(); [ set rtc time in the future ] 2) A thread try to turn off uie, however rtc_settime called by another thread turns on uie when they run in parallel. Consider the following sequence: CPU0 CPU1 ---- ---- ioctl(RTC_SET_TIME) ioctl(RTC_UIE_OFF) rtc->ops->set_time(); rtc_update_irq_enable(rtc, 0); rtc_update_irq_enable(rtc, 1); Fix it by guaranteeing that reading uie timer state, setting rtc time and enabling uie timer within a critical section. Fixes: 7e7c005b4b1f ("rtc: disable uie before setting time and enable after") Signed-off-by: Yu Liao --- drivers/rtc/interface.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c index bc55dd31bece..ef78e2977330 100644 --- a/drivers/rtc/interface.c +++ b/drivers/rtc/interface.c @@ -139,21 +139,23 @@ int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm) rtc_subtract_offset(rtc, tm); + err = mutex_lock_interruptible(&rtc->ops_lock); + if (err) + return err; + #ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL uie = rtc->uie_rtctimer.enabled || rtc->uie_irq_active; #else uie = rtc->uie_rtctimer.enabled; #endif if (uie) { - err = rtc_update_irq_enable(rtc, 0); - if (err) + err = __rtc_update_irq_enable(rtc, 0); + if (err) { + mutex_unlock(&rtc->ops_lock); return err; + } } - err = mutex_lock_interruptible(&rtc->ops_lock); - if (err) - return err; - if (!rtc->ops) err = -ENODEV; else if (rtc->ops->set_time) @@ -162,15 +164,17 @@ int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm) err = -EINVAL; pm_stay_awake(rtc->dev.parent); - mutex_unlock(&rtc->ops_lock); /* A timer might have just expired */ schedule_work(&rtc->irqwork); if (uie) { - err = rtc_update_irq_enable(rtc, 1); - if (err) + err = __rtc_update_irq_enable(rtc, 1); + if (err) { + mutex_unlock(&rtc->ops_lock); return err; + } } + mutex_unlock(&rtc->ops_lock); trace_rtc_set_time(rtc_tm_to_time64(tm), err); return err;