linux-kernel - Re: [PATCH] vsprintf: Make "null" pointer dereference more robust

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Date:   Tue, 06 Mar 2018 11:56:25 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Petr Mladek <pmladek@...e.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>
Subject: Re: [PATCH] vsprintf: Make "null" pointer dereference more robust

On Tue, 2018-03-06 at 10:25 +0100, Petr Mladek wrote:
> On Mon 2018-03-05 16:16:37, Rasmus Villemoes wrote:
> > On 2 March 2018 at 13:53, Petr Mladek <pmladek@...e.com> wrote:

> > > -       if (!ptr && *fmt != 'K' && *fmt != 'x') {
> > > +       if ((unsigned long)ptr < PAGE_SIZE && *fmt != 'K' && *fmt
> > > != 'x') {
> > 
> > ISTM that accidentally passing an ERR_PTR would be just as likely as
> > passing a NULL pointer (or some small offset from one), so if we do
> > this, shouldn't the test also cover IS_ERR values?
> 
> It would make perfect sense to catch IS_ERR_PTR(). Derefenrecing
> such pointer cause crash. But it might be pretty confusing to print
> "(null)" in this case.
> 
> I would handle this in separate patch and print "(err)" or so.
> Any volunteer to prepare the patch?

As I pointed out, we have already such check for %s in binary printf().
And it goes for "(null)". I'm not sure if changing that might break
something.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy