From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:37988 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751966AbeCWKBk (ORCPT ); Fri, 23 Mar 2018 06:01:40 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Guenter Roeck , Wim Van Sebroeck , Sasha Levin Subject: [PATCH 4.14 22/77] watchdog: Fix potential kref imbalance when opening watchdog Date: Fri, 23 Mar 2018 10:53:56 +0100 Message-Id: <20180323094143.684670232@linuxfoundation.org> In-Reply-To: <20180323094142.260022880@linuxfoundation.org> References: <20180323094142.260022880@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Guenter Roeck [ Upstream commit 4bcd615fad6adddc68b058d498b30a9e0e0db77a ] If a watchdog driver's open function sets WDOG_HW_RUNNING with the expectation that the watchdog can not be stopped, but then stops the watchdog anyway in its stop function, kref_get() wil not be called in watchdog_open(). If the watchdog then stops on close, WDOG_HW_RUNNING will be cleared and kref_put() will be called, causing a kref imbalance. As result the character device data structure will be released, which in turn will cause the system to crash on the next call to watchdog_open(). Fixes: ee142889e32f5 ("watchdog: Introduce WDOG_HW_RUNNING flag") Signed-off-by: Guenter Roeck Signed-off-by: Wim Van Sebroeck Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/watchdog/watchdog_dev.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -768,6 +768,7 @@ static int watchdog_open(struct inode *i { struct watchdog_core_data *wd_data; struct watchdog_device *wdd; + bool hw_running; int err; /* Get the corresponding watchdog device */ @@ -787,7 +788,8 @@ static int watchdog_open(struct inode *i * If the /dev/watchdog device is open, we don't want the module * to be unloaded. */ - if (!watchdog_hw_running(wdd) && !try_module_get(wdd->ops->owner)) { + hw_running = watchdog_hw_running(wdd); + if (!hw_running && !try_module_get(wdd->ops->owner)) { err = -EBUSY; goto out_clear; } @@ -798,7 +800,7 @@ static int watchdog_open(struct inode *i file->private_data = wd_data; - if (!watchdog_hw_running(wdd)) + if (!hw_running) kref_get(&wd_data->kref); /* dev/watchdog is a virtual (and thus non-seekable) filesystem */