linux-kernel - Re: [PATCH] staging: speakup: kobjects.c: fix char argument to %02x

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Message-ID: <874mfwqved.fsf@rasmusvillemoes.dk>
Date:	Sun, 06 Dec 2015 01:21:30 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Joe Perches <joe@...ches.com>
Cc:	William Hubbs <w.d.hubbs@...il.com>,
	Chris Brannon <chris@...-brannons.com>,
	Kirk Reiser <kirk@...sers.ca>,
	Samuel Thibault <samuel.thibault@...-lyon.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org, speakup@...ux-speakup.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: speakup: kobjects.c: fix char argument to %02x

On Sun, Dec 06 2015, Joe Perches <joe@...ches.com> wrote:

> On Sun, 2015-12-06 at 01:05 +0100, Rasmus Villemoes wrote:
>> If char is signed and ch happens to be negative, printing ch with
>> "%02x" will not do as intended (when ch is -19, one will get
>> "ffffffed"). Fix that by masking with 0xff.
>
> I presume there are a lot of these in the kernel.
> Did you use a tool to find this or just inspection?

Initially I just used coccinelle, for the most obvious candidates (with
--include-headers-for-types):

@r depends on !patch@
char c;
@@
* \( sprintf \| snprintf \| scnprintf \) (..., c, ...)

That gives lots of false positives (arguments to %c), but it's not too
bad piping to less, searching for "%[0.]2[xX]", and then checking
manually.

I'm now doing a much wider range of printf functions, but it's really
past my bedtime, so feel free to pick up the ball :-)

Rasmus
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