From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A7F8FC3A59B for ; Fri, 30 Aug 2019 20:47:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 83AA323439 for ; Fri, 30 Aug 2019 20:47:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728181AbfH3UrJ convert rfc822-to-8bit (ORCPT ); Fri, 30 Aug 2019 16:47:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:55832 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728079AbfH3UrJ (ORCPT ); Fri, 30 Aug 2019 16:47:09 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1104523439; Fri, 30 Aug 2019 20:47:07 +0000 (UTC) Date: Fri, 30 Aug 2019 16:47:06 -0400 From: Steven Rostedt To: "Naveen N. Rao" Cc: , Subject: Re: [PATCH 1/2] ftrace: Fix NULL pointer dereference in t_probe_next() Message-ID: <20190830164706.453a119e@gandalf.local.home> In-Reply-To: <05e021f757625cbbb006fad41380323dbe4e3b43.1562249521.git.naveen.n.rao@linux.vnet.ibm.com> References: <05e021f757625cbbb006fad41380323dbe4e3b43.1562249521.git.naveen.n.rao@linux.vnet.ibm.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 4 Jul 2019 20:04:41 +0530 "Naveen N. Rao" wrote: > kernel/trace/ftrace.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index 7b037295a1f1..0791eafb693d 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -3093,6 +3093,10 @@ t_probe_next(struct seq_file *m, loff_t *pos) > hnd = &iter->probe_entry->hlist; > > hash = iter->probe->ops.func_hash->filter_hash; > + > + if (!hash) > + return NULL; > + > size = 1 << hash->size_bits; > > retry: OK, I added this, but I'm also adding this on top: -- Steve >From 372e0d01da71c84dcecf7028598a33813b0d5256 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Fri, 30 Aug 2019 16:30:01 -0400 Subject: [PATCH] ftrace: Check for empty hash and comment the race with registering probes The race between adding a function probe and reading the probes that exist is very subtle. It needs a comment. Also, the issue can also happen if the probe has has the EMPTY_HASH as its func_hash. Cc: stable@vger.kernel.org Fixes: 7b60f3d876156 ("ftrace: Dynamically create the probe ftrace_ops for the trace_array") Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/ftrace.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 80beed2cf0da..6200a6fe10e3 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -3096,7 +3096,11 @@ t_probe_next(struct seq_file *m, loff_t *pos) hash = iter->probe->ops.func_hash->filter_hash; - if (!hash) + /* + * A probe being registered may temporarily have an empty hash + * and it's at the end of the func_probes list. + */ + if (!hash || hash == EMPTY_HASH) return NULL; size = 1 << hash->size_bits; @@ -4324,6 +4328,10 @@ register_ftrace_function_probe(char *glob, struct trace_array *tr, mutex_unlock(&ftrace_lock); + /* + * Note, there's a small window here that the func_hash->filter_hash + * may be NULL or empty. Need to be carefule when reading the loop. + */ mutex_lock(&probe->ops.func_hash->regex_lock); orig_hash = &probe->ops.func_hash->filter_hash; -- 2.20.1