linux-kernel - Re: [PATCH 2/3] tracing: make sure the parsed string always terminates with '\0'

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Message-ID: <20180115104950.u33gj7h4of7mlekx@intel.com>
Date:   Mon, 15 Jan 2018 18:49:50 +0800
From:   "Du, Changbin" <changbin.du@...el.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Du, Changbin" <changbin.du@...el.com>, jolsa@...hat.com,
        peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 2/3] tracing: make sure the parsed string always
 terminates with '\0'

On Tue, Jan 09, 2018 at 11:10:22PM -0500, Steven Rostedt wrote:
> On Wed, 10 Jan 2018 11:02:06 +0800
> "Du, Changbin" <changbin.du@...el.com> wrote:
> 
> > On Tue, Jan 09, 2018 at 06:02:58PM -0500, Steven Rostedt wrote:
> > > On Tue,  9 Jan 2018 17:55:47 +0800
> > > changbin.du@...el.com wrote:
> > >   
> > > > From: Changbin Du <changbin.du@...el.com>
> > > > 
> > > > The parser parse every string into parser.buffer. And some of the callers
> > > > assume that parser.buffer contains a C string. So it is dangerous that the
> > > > parser returns a unterminated string. The userspace can leverage this to
> > > > attack the kernel.  
> > > 
> > > Is this only a bug if we apply your first patch?
> > >  
> > I don't think so. Seems it is there already.
> >  
> 
> OK. I'll have to take a deeper look into this so that I completely
> understand the problem and your solution. I'm currently traveling and
> may not get to do that this week. Please ping me next week if you don't
> hear back from me on this issue.
> 
> Thanks!
> 
> -- Steve

I checked every trace_get_user() clients again and found it is not an issue in
current kernel. The client has checked trace_parser_cont() before using parsed
string or append '\0'.

I still want to make the parser returns a '\0' terminated string. Then we don't
require the clients append it. I think this would be better since we are dealing
with strings.

-- 
Thanks,
Changbin Du