linux-kernel - Re: [PATCH V2 1/2] tracing/probes: Fix a warning message to show correct maximum length

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Message-ID: <20170215103144.40561baf@gandalf.local.home>
Date:   Wed, 15 Feb 2017 10:31:44 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH V2 1/2] tracing/probes: Fix a warning message to show
 correct maximum length

On Thu, 16 Feb 2017 00:10:30 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Fri, 10 Feb 2017 11:04:34 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Fri, 10 Feb 2017 22:21:55 +0900
> > Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >   
> > > Since tracing/*probe_events will accept a probe definition
> > > up to 4096 - 2 ('\n' and '\0') bytes, it must show 4094 instead
> > > of 4096 in warning message.  
> > 
> > Actually, during the testing I found that we don't need the '\n'.
> > 
> > 	echo -n 'p:irq do_IRQ a=@...fies_64' > kprobe_events
> > 
> > works just fine. My tests work with 4095 characters. Before and after
> > my patch.  
> 
> Yeah, I see. I concider the case that if the writer writes 
> 4095 chars command + '\n' + next command, it will fail, that
> is what I pointed out below note.
> 
> > > 
> > > Note that there is one possible case of exceed 4094. If user
> > > prepare 4096 bytes null-terminated string and syscall write
> > > it with the count == 4095, then it can be accepted. However,
> > > if user puts a '\n' after that, it must rejected.
> > > So IMHO, the warning message should indicate shorter one,
> > > since it is safer.  
> 
> Thank you,
> 

OK, I'll just add the patch as is.

Thanks,

-- Steve