linux-kernel - Re: [PATCH v4 2/8] lib: add "on" and "off" to strtobool

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Date:	Tue, 19 Jan 2016 18:09:38 -0800
From:	Joe Perches <joe@...ches.com>
To:	Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...hat.com>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Mathias Krause <minipli@...glemail.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Arnd Bergmann <arnd@...db.de>, PaX Team <pageexec@...email.hu>,
	Emese Revfy <re.emese@...il.com>,
	kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v4 2/8] lib: add "on" and "off" to strtobool

On Tue, 2016-01-19 at 10:08 -0800, Kees Cook wrote:
> Several places in the kernel expect to use "on" and "off" for their
> boolean signifiers, so add them to strtobool.

Several places in the kernel use a char address like
fs/cifs/cifs_debug.c


	char c;
	...


	if (strtobool(&c, ...))

Using s[1] might cause problems for those uses.
> diff --git a/lib/string.c b/lib/string.c
[]
> @@ -635,12 +635,15 @@ EXPORT_SYMBOL(sysfs_streq);
>   * @s: input string
>   * @res: result
>   *
> - * This routine returns 0 iff the first character is one of 'Yy1Nn0'.
> - * Otherwise it will return -EINVAL.  Value pointed to by res is
> - * updated upon finding a match.
> + * This routine returns 0 iff the first character is one of 'Yy1Nn0', or
> + * [oO][NnFf] for "on" and "off". Otherwise it will return -EINVAL.  Value
> + * pointed to by res is updated upon finding a match.
>   */
>  int strtobool(const char *s, bool *res)
>  {
> +	if (!s)
> +		return -EINVAL;
> +
>  	switch (s[0]) {
>  	case 'y':
>  	case 'Y':
> @@ -652,6 +655,21 @@ int strtobool(const char *s, bool *res)
>  	case '0':
>  		*res = false;
>  		break;
> +	case 'o':
> +	case 'O':
> +		switch (s[1]) {
> +		case 'n':
> +		case 'N':
> +			*res = true;
> +			break;
> +		case 'f':
> +		case 'F':

Perhaps
		switch (tolower(s[1])) {
is more readable

> +			*res = false;
> +			break;
> +		default:
> +			return -EINVAL;
> +		}
> +		break;

or maybe /* fallthrough */

>  	default:
>  		return -EINVAL;
>  	}