From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753689AbcI1JL0 (ORCPT ); Wed, 28 Sep 2016 05:11:26 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:57675 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753511AbcI1JKk (ORCPT ); Wed, 28 Sep 2016 05:10:40 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Al Viro , Steven Rostedt Subject: [PATCH 4.7 32/69] tracing: Move mutex to protect against resetting of seq data Date: Wed, 28 Sep 2016 11:05:14 +0200 Message-Id: <20160928090446.426405735@linuxfoundation.org> X-Mailer: git-send-email 2.10.0 In-Reply-To: <20160928090445.054716307@linuxfoundation.org> References: <20160928090445.054716307@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 4.7-stable review patch. If anyone has any objections, please let me know. ------------------ From: Steven Rostedt (Red Hat) commit 1245800c0f96eb6ebb368593e251d66c01e61022 upstream. The iter->seq can be reset outside the protection of the mutex. So can reading of user data. Move the mutex up to the beginning of the function. Fixes: d7350c3f45694 ("tracing/core: make the read callbacks reentrants") Reported-by: Al Viro Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4890,19 +4890,20 @@ tracing_read_pipe(struct file *filp, cha struct trace_iterator *iter = filp->private_data; ssize_t sret; - /* return any leftover data */ - sret = trace_seq_to_user(&iter->seq, ubuf, cnt); - if (sret != -EBUSY) - return sret; - - trace_seq_init(&iter->seq); - /* * Avoid more than one consumer on a single file descriptor * This is just a matter of traces coherency, the ring buffer itself * is protected. */ mutex_lock(&iter->mutex); + + /* return any leftover data */ + sret = trace_seq_to_user(&iter->seq, ubuf, cnt); + if (sret != -EBUSY) + goto out; + + trace_seq_init(&iter->seq); + if (iter->trace->read) { sret = iter->trace->read(iter, filp, ubuf, cnt, ppos); if (sret)