linux-kernel - Re: [RFC][PATCH] tracing: Have traceprobe_probes_write() not access userspace unnecessarily

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Message-ID: <20170210075302.GB24405@gmail.com>
Date:   Fri, 10 Feb 2017 08:53:02 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH] tracing: Have traceprobe_probes_write() not access
 userspace unnecessarily


* Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Thu, 9 Feb 2017 18:04:58 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > 
> > The code in traceprobe_probes_write() reads up to 4096 bytes from userpace
> > for each line. If userspace passes in several lines to execute, the code
> > will do a large read for each line, even though, it is highly likely that
> > the first read from userspace received all of the lines at one.
> > 
> > I changed the logic to do a single read from userspace, and to only read
> > from userspace again if not all of the read from userspace made it in.
> > 
> > I tested this by adding printk()s and writing files that would test -1, ==,
> > and +1 the buffer size, to make sure that there's no overflows and that if a
> > single line is written with +1 the buffer size, that it fails properly.
> > 
> 
> Thanks Steve!
> 
> Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
> 
> BTW, this can conflict with my previous patch.
> 
> https://lkml.org/lkml/2017/2/6/1048
> https://lkml.org/lkml/2017/2/7/203
> 
> I'll update this. Ingo, Can I send these patch to Steve?

Sure, I've not applied your patch yet - mind sending it to Steve on top of Steve's 
patch?

Thanks,

	Ingo