Subject: Re: [PATCH] vsprintf: Do not break early boot with probing addresses

From: Andy Shevchenko <[email-masked]>
Date: Mon, 13 May 2019 12:13:20 +0300

On Mon, May 13, 2019 at 08:52:41AM +0000, David Laight wrote:
> From: christophe leroy
> > Sent: 10 May 2019 18:35
> > Le 10/05/2019 à 18:24, Steven Rostedt a écrit :
> > > On Fri, 10 May 2019 10:42:13 +0200
> > > Petr Mladek <[email-masked]> wrote:

> > >> -	if (probe_kernel_address(ptr, byte))
> > >> +	if ((unsigned long)ptr < PAGE_SIZE || IS_ERR_VALUE(ptr))
> > >>   		return "(efault)";
> 
> "efault" looks a bit like a spellling mistake for "default".

It's a special, thus it's in parenthesis, though somebody can be
misguided.

> > Usually, < PAGE_SIZE means NULL pointer dereference (via the member of a
> > struct)
> 
> Maybe the caller should pass in a short buffer so that you can return
> "(err-%d)"
> or "(null+%#x)" ?

In both cases it should be limited to the size of pointer (8 or 16
characters). Something like "(e:%4d)" would work for error codes.

The "(null)" is good enough by itself and already an established
practice..

-- 
With Best Regards,
Andy Shevchenko