From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753459AbaKZPWs (ORCPT ); Wed, 26 Nov 2014 10:22:48 -0500 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.225]:13190 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750973AbaKZPWq (ORCPT ); Wed, 26 Nov 2014 10:22:46 -0500 Date: Wed, 26 Nov 2014 10:22:44 -0500 From: Steven Rostedt To: Dan Carpenter Cc: Ingo Molnar , linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org Subject: Re: [patch] tracing: off by one in __trace_array_vprintk() Message-ID: <20141126102244.4bffa4b2@gandalf.local.home> In-Reply-To: <20141126150541.GU4893@mwanda> References: <20141126140621.GA18740@mwanda> <20141126092706.5d4038d4@gandalf.local.home> <20141126143719.GT4893@mwanda> <20141126094306.4f465616@gandalf.local.home> <20141126150541.GU4893@mwanda> X-Mailer: Claws Mail 3.10.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.130:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 26 Nov 2014 18:05:41 +0300 Dan Carpenter wrote: > On Wed, Nov 26, 2014 at 09:43:06AM -0500, Steven Rostedt wrote: > > I highly doubt it's much of a speed up. And we do that by sacrificing > > that one byte of buffer, which would lose the printk if len does equal > > TRACE_BUF_SIZE. > > > > I don't see a bug here. What exactly are you trying to fix? > > Heh. vsnprintf() is going to put a NUL char at the end of the string > even if you don't plan to use it. :P > > Another option would be to just print truncated output. We could use > vscnprintf() and remove the off by one limit check. Yes, that is a better patch. The previous one wasn't really fixing anything. But printing truncated output is better than nothing. Want to send it officially? Thanks, -- Steve > > regards, > dan carpenter > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 42a822d..ab76b7b 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -2160,9 +2160,7 @@ __trace_array_vprintk(struct ring_buffer *buffer, > goto out; > } > > - len = vsnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args); > - if (len > TRACE_BUF_SIZE) > - goto out; > + len = vscnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args); > > local_save_flags(flags); > size = sizeof(*entry) + len + 1; > @@ -2173,8 +2171,7 @@ __trace_array_vprintk(struct ring_buffer *buffer, > entry = ring_buffer_event_data(event); > entry->ip = ip; > > - memcpy(&entry->buf, tbuffer, len); > - entry->buf[len] = '\0'; > + memcpy(&entry->buf, tbuffer, len + 1); > if (!call_filter_check_discard(call, entry, buffer, event)) { > __buffer_unlock_commit(buffer, event); > ftrace_trace_stack(buffer, flags, 6, pc);