linux-kernel - Re: [PATCH v3 2/8] lib: add "on" and "off" to strtobool

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Date:	Fri, 11 Dec 2015 10:50:22 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Daniel Borkmann <daniel@...earbox.net>,
	Ingo Molnar <mingo@...hat.com>,
	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" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	PaX Team <pageexec@...email.hu>,
	Emese Revfy <re.emese@...il.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v3 2/8] lib: add "on" and "off" to strtobool

On Fri, Dec 11, 2015 at 9:00 AM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> On Wed, Dec 9, 2015 at 11:43 PM, Kees Cook <keescook@...omium.org> wrote:
>> Several places in the kernel expect to use "on" and "off" for their
>> boolean signifiers, so add them to strtobool.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
>> Cc: Daniel Borkmann <daniel@...earbox.net>
>> ---
>>  lib/string.c | 21 ++++++++++++++++++++-
>>  1 file changed, 20 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/string.c b/lib/string.c
>> index 0323c0d5629a..d7550432f91c 100644
>> --- a/lib/string.c
>> +++ b/lib/string.c
>> @@ -635,12 +635,16 @@ EXPORT_SYMBOL(sysfs_streq);
>>   * @s: input string
>>   * @res: result
>>   *
>> - * This routine returns 0 iff the first character is one of 'Yy1Nn0'.
>> + * This routine returns 0 iff the first character is one of 'Yy1Nn0', or
>> + * 'Oo' when the second character is one of 'fFnN' (for "on" and "off").
>
> Maybe
>
> …or [Oo][FfNn] for "off" and "on"…

Sure! That's more readable.

>>   * 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;
>> +
>
> This change I think is better to do separately. Do we have even need for it?

I'm happy to separate it, sure. I added it here because several of the
__setup and param callers do a check for !NULL input, and it made this
cleaner. Also it seems sensible to do this check anyway.

>>         switch (s[0]) {
>>         case 'y':
>>         case 'Y':
>> @@ -652,6 +656,21 @@ 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':
>> +                       *res = false;
>> +                       break;
>
>
>> +               default:
>> +                       return -EINVAL;
>> +               }
>> +               break;
>>         default:
>>                 return -EINVAL;
>
> Maybe in both cases
> default:
>  break;
> }
> …
> }
> return -EINVAL;

I went back and forth on this. To switch to the fall-back being EINVAL
meant I had to change all the other "breaks" into "return 0", and it
just looked ugly to me. If that is preferred, though, I'm happy to do
it.

Thanks!

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security
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