RE: [PATCH] vsprintf: avoid misleading "(null)" for %px

[Roberts, William C]

> -----Original Message-----
> From: Tobin C. Harding [mailto:me@xxxxxxxx]
> Sent: Monday, February 5, 2018 2:23 PM
> To: Adam Borowski <kilobyte@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>; Petr Mladek <pmladek@xxxxxxxx>;
> Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>; Steven Rostedt
> <rostedt@xxxxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>; Andrew Morton
> <akpm@xxxxxxxxxxxxxxxxxxxx>; Joe Perches <joe@xxxxxxxxxxx>; Roberts,
> William C <william.c.roberts@xxxxxxxxx>; Linus Torvalds <torvalds@linux-
> foundation.org>; David Laight <David.Laight@xxxxxxxxxx>; Randy Dunlap
> <rdunlap@xxxxxxxxxxxxx>; Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Subject: Re: [PATCH] vsprintf: avoid misleading "(null)" for %px
> 
> On Mon, Feb 05, 2018 at 09:58:17PM +0100, Adam Borowski wrote:
> > On Tue, Feb 06, 2018 at 07:32:32AM +1100, Kees Cook wrote:
> > > On Tue, Feb 6, 2018 at 7:15 AM, Tobin C. Harding <me@xxxxxxxx> wrote:
> > > > On Tue, Feb 06, 2018 at 05:57:17AM +1100, Kees Cook wrote:
> > > >> On Mon, Feb 5, 2018 at 8:44 PM, Petr Mladek <pmladek@xxxxxxxx>
> wrote:
> > > >> > On Sun 2018-02-04 18:45:21, Adam Borowski wrote:
> > > >> >> Like %pK already does, print "00000000" instead.
> > > >> >>
> > > >> >> This confused people -- the convention is that "(null)" means
> > > >> >> you tried to dereference a null pointer as opposed to printing the
> address.
> > > >
> > > > Leaving aside what is converting to %px.  If we consider that
> > > > using %px is meant to convey to us that we _really_ want the
> > > > address, in hex hence the 'x', then it is not surprising that we
> > > > will get "00000000"'s for a null pointer, right?  Yes it is
> > > > different to before but since we are changing the specifier does
> > > > this not imply that there may be some change?
> > >
> > > I personally prefer 0000s, but if we're going to change this, we
> > > need to be aware of the difference.
> >
> > It's easy to paint this bikeshed any color you guys want to: there's an "if"
> > already.  My preference is also 0000; NULL would be good, too -- I
> > just don't want (null) as that has a special meaning in usual
> > userspace implementations; (null) also fits well most other modes of
> > %p as they show some object the argument points to.  Confusion = wasted
> debugging time.
> >
> > This is consistent with what we had before, with %pK special-cased.
> >
> > > > In what is now to be expected fashion for %p the discussion
> > > > appears to have split into two different things - what to do with
> > > > %px and what to do with %pK :)
> > >
> > > I say leave %pK alone. :)
> >
> > As in, printing some random (hashed) value?
> >
> >
> > Let's recap:
> >
> > Currently:
> >               not-null              null
> > %pponies      object's description  (null)
> > %px           address               (null)
> > %pK           hash                  hash
> >
> > I'd propose:
> >               not-null              null
> > %pponies      object's description  (null)
> > %px           address               00000000
> > %pK           hash                  00000000
> >
> > The initial patch in this thread changes printk("%px",0) from (null)
> > to 00000000; what Tobin complained about is that printk("%pK",0) prints a
> > random value.
> 
> Epic fail on my behalf, my first comment was _wrong_ and brought %pK into the
> discussion - bad Tobin, please crawl back under your rock.
> 
> The original patch is good IMO and I AFAICT in everyone else's.
Nod.
> 
> 	Tobin