netdev - Re: [PATCH v2 2/4] lib: update single-char callers of strtobool

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Date:	Fri, 5 Feb 2016 13:18:04 -0800
From:	Kees Cook <keescook@...omium.org>
To:	David Laight <David.Laight@...lab.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Amitkumar Karwar <akarwar@...vell.com>,
	Nishant Sarmukadam <nishants@...vell.com>,
	Kalle Valo <kvalo@...eaurora.org>,
	Steve French <sfrench@...ba.org>,
	"linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
	Joe Perches <joe@...ches.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Daniel Borkmann <daniel@...earbox.net>,
	Michael Ellerman <mpe@...erman.id.au>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/4] lib: update single-char callers of strtobool

On Fri, Feb 5, 2016 at 2:46 AM, David Laight <David.Laight@...lab.com> wrote:
> From: Kees Cook
>> Sent: 04 February 2016 21:01
>> Some callers of strtobool were passing a pointer to unterminated strings.
>> In preparation of adding multi-character processing to kstrtobool, update
>> the callers to not pass single-character pointers, and switch to using the
>> new kstrtobool_from_user helper where possible.
>
> Personally I think you should change the name of the function so that the
> compiler (and linker) will pick up places that have not been changed.
> Relying on people to make the required changes will cause problems.

After the single-character users were pointed out, I looked for others
and there aren't any.

> The current code (presumably) treats "no", "nyet" and "nkjkkrkjrkjterkj" as false.
> Changing that behaviour will break things.

There's no change there. All three of those will still be "false".
Perhaps my changelog shouldn't say "unterminated" but rather
"character array".

> If you want to support "on" and "off", then maybe check for the supplied string
> starting with the character sequences "on\0" and "off\0" (as well as any others).
> This doesn't need the input string be '\0' terminated - since you match y and n
> without looking at the 2nd byte.
> You'd have to be extremely unlucky to get a page fault in the 3 bytes
> following an 'o' if the caller supplied a single byte buffer.

I'd prefer to keep the switch statement as short as possible, and I
don't want to do full string compares. And as you say, even fixing the
single-byte callers seems like a needless exercise, but seeing as how
it's a net clean-up, I think it's good they way I've got the series.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security