From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759980AbcCDQRT (ORCPT ); Fri, 4 Mar 2016 11:17:19 -0500 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:60551 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759116AbcCDQCZ (ORCPT ); Fri, 4 Mar 2016 11:02:25 -0500 Message-Id: <20160304153001.538300093@1wt.eu> User-Agent: quilt/0.63-1 Date: Fri, 04 Mar 2016 16:30:19 +0100 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Dmitry Vyukov , Johannes Berg , Ben Hutchings , Willy Tarreau Subject: [PATCH 2.6.32 19/55] rfkill: fix rfkill_fop_read wait_event usage MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 In-Reply-To: <148ee355b419e9976ca727513a1405c8@local> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.32-longterm 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: Ben Hutchings Signed-off-by: Willy Tarreau --- net/rfkill/core.c | 16 ++++------------ 1 file changed, 4 insertions(+), 12 deletions(-) diff --git a/net/rfkill/core.c b/net/rfkill/core.c index 85334a0..898f8cf 100644 --- a/net/rfkill/core.c +++ b/net/rfkill/core.c @@ -1037,17 +1037,6 @@ static unsigned int rfkill_fop_poll(struct file *file, poll_table *wait) 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) { @@ -1064,8 +1053,11 @@ static ssize_t rfkill_fop_read(struct file *file, char __user *buf, 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) -- 1.7.12.2.21.g234cd45.dirty