linux-kernel - Re: [PATCH] jsm_tty: Fix a possible null pointer dereference in two functions

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Message-ID: <1511979367.19952.71.camel@perches.com>
Date:   Wed, 29 Nov 2017 10:16:07 -0800
From:   Joe Perches <joe@...ches.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     SF Markus Elfring <elfring@...rs.sourceforge.net>,
        linux-serial@...r.kernel.org,
        "Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>,
        Jiri Slaby <jslaby@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] jsm_tty: Fix a possible null pointer dereference in two
 functions

On Wed, 2017-11-29 at 18:05 +0000, Greg Kroah-Hartman wrote:
> On Wed, Nov 29, 2017 at 09:51:36AM -0800, Joe Perches wrote:
> > On Wed, 2017-11-29 at 17:35 +0000, Greg Kroah-Hartman wrote:
> > > On Wed, Nov 29, 2017 at 09:23:07AM -0800, Joe Perches wrote:
> > > > On Wed, 2017-11-29 at 17:40 +0100, SF Markus Elfring wrote:
> > > > > From: Markus Elfring <elfring@...rs.sourceforge.net>
> > > > > Date: Wed, 29 Nov 2017 17:30:36 +0100
> > > > > 
> > > > > Move two debug messages so that a null pointer access can not happen
> > > > > for the variable "ch" in these functions.
> > > > 
> > > > An actual defect fix!
> > > 
> > > Nope, not at all, this does not "fix" anything.
> > 
> > Well, I believe it does in unusual cases like a
> > CONFIG_DYNAMIC_DEBUG when this is enabled by an
> > odd +p in the dynamic debug control file.
> > 
> > > > Here you could probably cc stable too.
> > > 
> > > Nope, not worth it.
> > 
> > <shrug>
> > 
> > It's pretty unlikely, but it is an actual defect.
> 
> No it is not, those variables will never be set to NULL, so this can
> never be triggered.  Walk up the call chain.

Right you are.  Local analysis isn't enough.
The code could/should be removed, but it's not a defect.

cheers, Joe