linux-kernel - Re: [PATCH] vsprintf: don't obfuscate NULL and error pointers

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Message-ID: <CAOi1vP_Ned9QG32+o9KT-Bh3qMTb6h0SaP8W74Am_gkVX3mcSQ@mail.gmail.com>
Date:   Tue, 18 Feb 2020 21:19:06 +0100
From:   Ilya Dryomov <idryomov@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Adam Borowski <kilobyte@...band.pl>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "Tobin C . Harding" <me@...in.cc>
Subject: Re: [PATCH] vsprintf: don't obfuscate NULL and error pointers

On Tue, Feb 18, 2020 at 8:39 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Tue, Feb 18, 2020 at 11:31 AM Adam Borowski <kilobyte@...band.pl> wrote:
> >
> > Either "0" or "NULL" (or "∅" if you allow cp437-subset Unicode ) wouldn't
> > cause such confusion.
>
> An all-uppercase "NULL" probably matches the error code printout
> syntax better too, and is more clearly a pointer.
>
> And with %pe you can't assume columnar output anyway (unless you
> explicitly ask for some width), so the length of the output cannot
> matter.
>
> So yeah, I agree. To extend on Ilya's example:
>
>                               ptr        error-ptr             NULL
>   %p:            0000000001f8cc5b fffffffffffffff2 0000000000000000
>   %pK, kptr = 0: 0000000001f8cc5b fffffffffffffff2 0000000000000000
>   %px:           ffff888048c04020 fffffffffffffff2 0000000000000000
>   %pK, kptr = 1: ffff888048c04020 fffffffffffffff2 0000000000000000
>   %pK, kptr = 2: 0000000000000000 0000000000000000 0000000000000000
>   %p:            0000000001f8cc5b -EFAULT NULL

    ^^^
I assume you meant %pe here.

>
> would seem to be a sane output format. Hmm?

Looks sensible to me.  Without this patch NULL is obfuscated for
both %p and %pe though.  Do you want this patch amended or prefer
a follow-up for %pe "0000000000000000" -> "NULL" so that it can be
discussed separately?

Thanks,

                Ilya