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

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Date:   Tue, 14 May 2019 21:13:06 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     David Laight <David.Laight@...lab.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        christophe leroy <christophe.leroy@....fr>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Russell Currey <ruscur@...sell.cc>,
        Stephen Rothwell <sfr@...abs.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing addresses

Hi Steve,

On Tue, May 14, 2019 at 8:37 PM Steven Rostedt <rostedt@...dmis.org> wrote:
> On Tue, 14 May 2019 11:02:17 +0200
> Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > On Tue, May 14, 2019 at 10:29 AM David Laight <David.Laight@...lab.com> wrote:
> > > > And I like Steven's "(fault)" idea.
> > > > How about this:
> > > >
> > > >       if ptr < PAGE_SIZE              -> "(null)"
> > > >       if IS_ERR_VALUE(ptr)            -> "(fault)"
> > > >
> > > >       -ss
> > >
> > > Or:
> > >         if (ptr < PAGE_SIZE)
> > >                 return ptr ? "(null+)" : "(null)";
>
> Hmm, that is useful.
>
> > >         if IS_ERR_VALUE(ptr)
> > >                 return "(errno)"
>
> I still prefer "(fault)" as is pretty much all I would expect from a
> pointer dereference, even if it is just bad parsing of, say, a parsing
> an MAC address. "fault" is generic enough. "errno" will be confusing,
> because that's normally a variable not a output.
>
> >
> > Do we care about the value? "(-E%u)"?
>
> That too could be confusing. What would (-E22) be considered by a user
> doing an sprintf() on some string. I know that would confuse me, or I
> would think that it was what the %pX displayed, and wonder why it
> displayed it that way. Whereas "(fault)" is quite obvious for any %p
> use case.

I would immediately understand there's a missing IS_ERR() check in a
function that can return  -EINVAL, without having to add a new printk()
to find out what kind of bogus value has been received, and without
having to reboot, and trying to reproduce...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds