linux-kernel - Re: [PATCH v2 2/5] string_helpers: add kstrdup_quotable

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Date:	Wed, 6 Apr 2016 16:38:17 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kalle Valo <kvalo@...eaurora.org>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Joe Perches <joe@...ches.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Jiri Slaby <jslaby@...e.com>, Paul Moore <pmoore@...hat.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Andreas Gruenbacher <agruenba@...hat.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] string_helpers: add kstrdup_quotable_cmdline

On Wed, Mar 30, 2016 at 4:11 AM, Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
> On Wed, 2016-03-30 at 14:07 +0300, Andy Shevchenko wrote:
>> On Mon, 2016-03-28 at 14:14 -0700, Kees Cook wrote:
>
>
>> > +   res = get_cmdline(task, buffer, PAGE_SIZE - 1);
>> > +   buffer[res] = '\0';
>> > +
>> > +   /* Collapse trailing NULLs. */
>> > +   for (; res > 0; res--)
>> > +           if (buffer[res-1] != '\0')
>> > +                   break;
>> /* buffer[res] is '\0', so, predecrement is safe here */
>> while (buffer[--res] == '\0')
>>  /* nothing */;
>>
>> ?
>>
>
> Oops, no, the following should be better
>
> while (--res >= 0 && buffer[res] == '\0') ;

Sure, I'll change it. Though I'll need to adjust the next loop's use
of res (since it effectively changes from "number of bytes" counter to
"location of last non-null byte" (i <= res).

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security