From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Joe Perches <joe@perches.com>, Arnd Bergmann <arnd@kernel.org>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>,
David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
Shawn Guo <shawnguo@kernel.org>,
Sascha Hauer <s.hauer@pengutronix.de>,
Pengutronix Kernel Team <kernel@pengutronix.de>,
Fabio Estevam <festevam@gmail.com>,
NXP Linux Team <linux-imx@nxp.com>,
Marco Felsch <m.felsch@pengutronix.de>,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
Liu Ying <victor.liu@nxp.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC patch] vsprintf: Allow %pe to print non PTR_ERR %pe uses as decimal
Date: Wed, 24 Mar 2021 22:27:41 +0100 [thread overview]
Message-ID: <3d66137e-7842-2764-456f-7cc9e54a6d2e@rasmusvillemoes.dk> (raw)
In-Reply-To: <d184069de43135a9c9e5f031447faf98ab3f437d.camel@perches.com>
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.
If you want to print the pointer value just do %px. No need for silly
games. What I'm talking about is preventing _un_intentionally leaking a
valid kernel pointer value. So no, a non-ERR_PTR passed to %pe is not
going to be printed as-is, not in decimal or hexadecimal or roman numerals.
>> If the code wants a cute -EFOO string explaining what's wrong, what
>> about "%pe", ERR_PTR(mux < 0 : mux : -ERANGE)? Or two separate error
>> messages
>>
>> if (mux < 0)
>> ...
>> else if (mux >= ARRAY_SIZE())
>> ...
>
> Multiple tests, more unnecessary code, multiple format strings, etc...
Agreed, I'm not really advocating for the latter; the former suggestion
is IMO a pretty concise way of providing useful information in dmesg.
Rasmus
next prev parent reply other threads:[~2021-03-24 21:28 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-24 12:17 [PATCH] [v2] drm/imx: imx-ldb: fix out of bounds array access warning Arnd Bergmann
2021-03-24 14:20 ` Joe Perches
2021-03-24 16:42 ` Arnd Bergmann
2021-03-24 16:52 ` Joe Perches
2021-03-24 17:20 ` [RFC patch] vsprintf: Allow %pe to print non PTR_ERR %pe uses as decimal Joe Perches
2021-03-24 17:33 ` Rasmus Villemoes
2021-03-24 19:24 ` Joe Perches
2021-03-24 21:27 ` Rasmus Villemoes [this message]
2021-03-24 22:18 ` Joe Perches
2021-03-24 22:36 ` Rasmus Villemoes
2021-03-24 22:46 ` Joe Perches
2021-03-24 16:14 ` [PATCH] [v2] drm/imx: imx-ldb: fix out of bounds array access warning kernel test robot
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