linux-kernel - Re: [RFC patch] vsprintf: Allow %pe to print non PTR

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <9d320cd403921f4b36b726b71a51572463599cf5.camel@perches.com>
Date:   Wed, 24 Mar 2021 15:18:35 -0700
From:   Joe Perches <joe@...ches.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Arnd Bergmann <arnd@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Liu Ying <victor.liu@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC patch] vsprintf: Allow %pe to print non PTR_ERR %pe uses
 as decimal

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.