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

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Date:   Mon, 5 Mar 2018 15:53:06 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     "Tobin C . Harding" <me@...in.cc>, linux@...musvillemoes.dk,
        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 Fri 2018-03-02 16:17:34, Andy Shevchenko wrote:
> On Fri, 2018-03-02 at 13:53 +0100, Petr Mladek wrote:
> > %p has many modifiers where the pointer is dereferenced. An invalid
> > pointer might cause kernel to crash silently.
> > 
> > Note that printk() formats the string under logbuf_lock. Any recursive
> > printks are redirected to the printk_safe implementation and the
> > messages
> > are stored into per-CPU buffers. These buffers might be eventually
> > flushed
> > in printk_safe_flush_on_panic() but it is not guaranteed.
> > 
> > In general, we should do our best to get useful message from printk().
> > All pointers to the first memory page must be invalid. Let's prevent
> > the dereference and print "(null)" in this case. This is already done
> > in many other situations, including "%s" format handling and many
> > page fault handlers.
> > 
> 
> 
> With such explanation it makes at least clear for the reader why it's
> done.
> 
> Thanks!
> 
> Would you be okay if I take this one as a first in my series and
> resubmit the series based on it?

Makes sense. Feel free to go on.

Best Regards,
Petr