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

Petr Mladek
2019-05-13T12:42:20Z

On Mon 2019-05-13 12:13:20, Andy Shevchenko wrote:
> 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 <pmladek@suse.com> 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)" ?

There are many vsprintf() users. I am afraid that nobody would want
to define extra buffers for error messages. It must fit into
the one for the formatted string.

> 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.

I am afraid that we could get 10 different proposals from a huge
enough group of people. I wanted to start with something simple
(source code). I know that (efault) might be confused with
"default" but it is still just one string to grep.

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

(efault) made more sense with the probe_kernel_read() that
checked wide range of addresses. Well, I still think that
it makes sense to distinguish a pure NULL. And it still
used also for IS_ERR_VALUE().

Best Regards,
Petr