Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757555Ab3EQVqP (ORCPT ); Fri, 17 May 2013 17:46:15 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:54312 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757198Ab3EQVhw (ORCPT ); Fri, 17 May 2013 17:37:52 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Arkadiusz Miskiewicz , Guenter Roeck , Wim Van Sebroeck Subject: [ 076/102] watchdog: Fix race condition in registration code Date: Fri, 17 May 2013 14:36:31 -0700 Message-Id: <20130517213252.311871344@linuxfoundation.org> X-Mailer: git-send-email 1.8.3.rc0.20.gb99dd2e In-Reply-To: <20130517213244.277411019@linuxfoundation.org> References: <20130517213244.277411019@linuxfoundation.org> User-Agent: quilt/0.60-5.1.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2023 Lines: 61 3.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Guenter Roeck commit 60403f7a4d9368d187f79cba5e4672d01df37574 upstream. A race condition exists when registering the first watchdog device. Sequence of events: - watchdog_register_device calls watchdog_dev_register - watchdog_dev_register creates the watchdog misc device by calling misc_register. At that time, the matching character device (/dev/watchdog0) does not yet exist, and old_wdd is not set either. - Userspace gets an event and opens /dev/watchdog - watchdog_open is called and sets wdd = old_wdd, which is still NULL, and tries to dereference it. This causes the kernel to panic. Seen with systemd trying to open /dev/watchdog immediately after it was created. Reported-by: Arkadiusz Miskiewicz Signed-off-by: Guenter Roeck Tested-by: Arkadiusz Miskiewicz Signed-off-by: Wim Van Sebroeck Signed-off-by: Greg Kroah-Hartman --- drivers/watchdog/watchdog_dev.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -523,6 +523,7 @@ int watchdog_dev_register(struct watchdo int err, devno; if (watchdog->id == 0) { + old_wdd = watchdog; watchdog_miscdev.parent = watchdog->parent; err = misc_register(&watchdog_miscdev); if (err != 0) { @@ -531,9 +532,9 @@ int watchdog_dev_register(struct watchdo if (err == -EBUSY) pr_err("%s: a legacy watchdog module is probably present.\n", watchdog->info->identity); + old_wdd = NULL; return err; } - old_wdd = watchdog; } /* Fill in the data structures */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/