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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 163FBC38A02 for ; Wed, 26 Oct 2022 03:35:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233058AbiJZDfL (ORCPT ); Tue, 25 Oct 2022 23:35:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54574 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232981AbiJZDe6 (ORCPT ); Tue, 25 Oct 2022 23:34:58 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 98F8A33E0A; Tue, 25 Oct 2022 20:34:51 -0700 (PDT) Received: from dggpeml500020.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4MxvVN1ckzzpVrr; Wed, 26 Oct 2022 11:31:24 +0800 (CST) Received: from dggpeml500003.china.huawei.com (7.185.36.200) by dggpeml500020.china.huawei.com (7.185.36.88) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 26 Oct 2022 11:34:49 +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, 26 Oct 2022 11:34:49 +0800 From: Yu Liao To: , CC: , , , Subject: [RFC PATCH 2/2] rtc: fix race condition in rtc_set_time() Date: Wed, 26 Oct 2022 11:33:48 +0800 Message-ID: <20221026033348.1660732-3-liaoyu15@huawei.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20221026033348.1660732-1-liaoyu15@huawei.com> References: <20221026033348.1660732-1-liaoyu15@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.103.91] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpeml500003.china.huawei.com (7.185.36.200) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c index bc55dd31bece..00a6173d8895 100644 --- a/drivers/rtc/interface.c +++ b/drivers/rtc/interface.c @@ -139,21 +139,21 @@ 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); + err = __rtc_update_irq_enable(rtc, 0); if (err) 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 +162,15 @@ 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); + err = __rtc_update_irq_enable(rtc, 1); if (err) return err; } + mutex_unlock(&rtc->ops_lock); trace_rtc_set_time(rtc_tm_to_time64(tm), err); return err; -- 2.25.1