From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756835AbcCBCOt (ORCPT ); Tue, 1 Mar 2016 21:14:49 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:45938 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753180AbcCAXrW (ORCPT ); Tue, 1 Mar 2016 18:47:22 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dmitry Vyukov , Johannes Berg Subject: [PATCH 3.10 70/80] rfkill: fix rfkill_fop_read wait_event usage Date: Tue, 1 Mar 2016 15:46:04 -0800 Message-Id: <20160301234351.874672207@linuxfoundation.org> X-Mailer: git-send-email 2.7.2 In-Reply-To: <20160301234349.667990420@linuxfoundation.org> References: <20160301234349.667990420@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Johannes Berg commit 6736fde9672ff6717ac576e9bba2fd5f3dfec822 upstream. The code within wait_event_interruptible() is called with !TASK_RUNNING, so mustn't call any functions that can sleep, like mutex_lock(). Since we re-check the list_empty() in a loop after the wait, it's safe to simply use list_empty() without locking. This bug has existed forever, but was only discovered now because all userspace implementations, including the default 'rfkill' tool, use poll() or select() to get a readable fd before attempting to read. Fixes: c64fb01627e24 ("rfkill: create useful userspace interface") Reported-by: Dmitry Vyukov Signed-off-by: Johannes Berg Signed-off-by: Greg Kroah-Hartman --- net/rfkill/core.c | 16 ++++------------ 1 file changed, 4 insertions(+), 12 deletions(-) --- a/net/rfkill/core.c +++ b/net/rfkill/core.c @@ -1088,17 +1088,6 @@ static unsigned int rfkill_fop_poll(stru return res; } -static bool rfkill_readable(struct rfkill_data *data) -{ - bool r; - - mutex_lock(&data->mtx); - r = !list_empty(&data->events); - mutex_unlock(&data->mtx); - - return r; -} - static ssize_t rfkill_fop_read(struct file *file, char __user *buf, size_t count, loff_t *pos) { @@ -1115,8 +1104,11 @@ static ssize_t rfkill_fop_read(struct fi goto out; } mutex_unlock(&data->mtx); + /* since we re-check and it just compares pointers, + * using !list_empty() without locking isn't a problem + */ ret = wait_event_interruptible(data->read_wait, - rfkill_readable(data)); + !list_empty(&data->events)); mutex_lock(&data->mtx); if (ret)