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

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Message-ID: <1520263504.10722.399.camel@linux.intel.com>
Date:   Mon, 05 Mar 2018 17:25:04 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Petr Mladek <pmladek@...e.com>
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 Mon, 2018-03-05 at 16:16 +0100, 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?

We (will) have such check in two places, perhaps a helper

static bool is_pointer_valid(void *ptr)
{
  return !IS_ERR(ptr) && (unsigned long)ptr >= PAGE_SIZE;
}

?

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