From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755750AbaKSOkQ (ORCPT ); Wed, 19 Nov 2014 09:40:16 -0500 Received: from cantor2.suse.de ([195.135.220.15]:57912 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754697AbaKSOkN (ORCPT ); Wed, 19 Nov 2014 09:40:13 -0500 Date: Wed, 19 Nov 2014 15:40:05 +0100 From: Petr Mladek To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Jiri Kosina Subject: Re: [PATCH 2/2] tracing: Use trace_seq_used() and seq_buf_used() instead of len Message-ID: <20141119144004.GB2332@dhcp128.suse.cz> References: <20141115045847.712848224@goodmis.org> <20141115050603.904875201@goodmis.org> <20141117123250.10f6f57c@gandalf.local.home> <20141117141215.2dbd5f12@gandalf.local.home> <20141118163354.GK23958@pathway.suse.cz> <20141118123732.462b1ad8@gandalf.local.home> <20141119114017.GA2332@dhcp128.suse.cz> <20141119084800.524beb62@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141119084800.524beb62@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 2014-11-19 08:48:00, Steven Rostedt wrote: > On Wed, 19 Nov 2014 12:40:17 +0100 > Petr Mladek wrote: > > > > > > > > > There is one more dangerous usage in trace_printk_seq(). It is on > > > > three lines there. > > > > > > You totally confused me. What usage in trace_printk_seq(), and what > > > three lines? > > > > > The confusion is caused by the 'k' ("print" vs. "printk") in the > > function name. I was talking about the following function from > > kernel/trace/trace.c: > > Silly 'k', Trix are for kids! :-) > > > > void > > trace_printk_seq(struct trace_seq *s) > > { > > /* Probably should print a warning here. */ > > if (s->seq.len >= TRACE_MAX_PRINT) > > s->seq.len = TRACE_MAX_PRINT; > > > > /* should be zero ended, but we are paranoid. */ > > s->buffer[s->seq.len] = 0; > > > > printk(KERN_TRACE "%s", s->buffer); > > > > trace_seq_init(s); > > } > > > > I found it when checking the applied patches in origin/rfc/seq-buf > > branch. I hope that it was the correct place. > > Yes, that's the working branch for this code. > > Anyway, I saw this and thought about using trace_seq_used(), but then I > realized that this is trace_seq code which has a hard coded buffer > length of PAGE_SIZE which on all archs is more than 1000 > (TRACE_MAX_PRINT). > > Regardless of overflow or not (or even if trace_seq is full), that if > statement will prevent this from doing any buffer overflows. > > s->seq.len will never be more than s->seq.size after the test against > TRACE_MAX_PRINT. So I see no harm here. Ah, I see. Well, I would feel more comfortable if it uses trace_seq_used() or if there is some explanation in a comment. But you are right, it is safe as it is. Feel free to leave it. Reviewed-by: Petr Mladek Best Regards, Petr