Re: [RFC patch] vsprintf: Allow %pe to print non PTR_ERR %pe uses as decimal

[Joe Perches]

On Wed, 2021-03-24 at 22:27 +0100, Rasmus Villemoes wrote:
> On 24/03/2021 20.24, Joe Perches wrote:
> > On Wed, 2021-03-24 at 18:33 +0100, Rasmus Villemoes wrote:
> > > On 24/03/2021 18.20, Joe Perches wrote:
> > > 
> > > > 
> > > > Maybe it's better to output non PTR_ERR %pe uses as decimal so this
> > > > sort of code would work.
> > > 
> > > No, because that would leak the pointer value when somebody has
> > > accidentally passed a real kernel pointer to %pe.
> > 
> > I think it's not really an issue.
> > 
> > _All_ code that uses %p<foo> extensions need inspection anyway.
> 
> There are now a bunch of sanity checks in place that catch e.g. an
> ERR_PTR passed to an extension that would derefence the pointer;
> enforcing that only ERR_PTRs are passed to %pe (or falling back to %p)
> is another of those safeguards.
> 
> > It's already possible to intentionally 'leak' the ptr value
> > by using %pe, -ptr so I think that's not really an issue.
> > 
> 
> Huh, what? I assume -ptr is shorthand for (void*)-(unsigned long)ptr.
> How would that leak the value if ptr is an ordinary kernel pointer?
> That's not an ERR_PTR unless (unsigned long)ptr is < 4095 or so.

You are confusing ERR_PTR with IS_ERR

ERR_PTR is just

include/linux/err.h:static inline void * __must_check ERR_PTR(long error)
include/linux/err.h-{
include/linux/err.h-    return (void *) error;
include/linux/err.h-}f 

> If you want to print the pointer value just do %px. No need for silly
> games.

There's no silly game here.  %pe would either print a string or a value.
It already does that in 2 cases.