linux-kernel - Re: [PATCH 1/2] RAS/CEC: Use the right length for "cec

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Date:   Sat, 7 Oct 2017 16:29:35 +0200
From:   Nicolas Iooss <nicolas.iooss_linux@....org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] RAS/CEC: Use the right length for "cec_disable"

On Tue, Oct 3, 2017 at 11:04 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Mon, Oct 02, 2017 at 05:42:56PM +0200, Thomas Gleixner wrote:
>> On Mon, 2 Oct 2017, Borislav Petkov wrote:
>> > From: Nicolas Iooss <nicolas.iooss_linux@....org>
>> >
>> > parse_cec_param() compares a string with "cec_disable" using only 7
>> > characters of the 11-character-long string. Fix the length.
>> >
>> > Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@....org>
>> > Fixes: 011d82611172 ("RAS: Add a Corrected Errors Collector")
>> > Link: http://lkml.kernel.org/r/20170903075440.30250-1-nicolas.iooss_linux@m4x.org
>> > Signed-off-by: Borislav Petkov <bp@...e.de>
>> > ---
>> >  drivers/ras/cec.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/ras/cec.c b/drivers/ras/cec.c
>> > index d0e5d6ee882c..586c296d1538 100644
>> > --- a/drivers/ras/cec.c
>> > +++ b/drivers/ras/cec.c
>> > @@ -523,7 +523,7 @@ int __init parse_cec_param(char *str)
>> >     if (*str == '=')
>> >             str++;
>> >
>> > -   if (!strncmp(str, "cec_disable", 7))
>> > +   if (!strncmp(str, "cec_disable", 11))
>>
>> This kind of issue happens over and over. So if you really want to use
>> strncmp() then this should be:
>>
>> #define       CEC_DISABLE     "cec_disable"
>>
>>       if (!strncmp(str, CEC_DISABLE, strlen(CEC_DISABLE))
>>
>> or we get a proper helper for that. Though in case of comparing some string
>> against a constant string strncmp() has no real advantage over strcmp() as
>> the comparison is guaranteed to be bound by the string constant.
>
> Right.
>
> Nicolas, wanna address that?
>
> Thx.

Hi, the only difference I see between strncmp+strlen and strcmp is
that the first option compares a prefix ("does the string begin with
cec_disable?") and the second one checks that strings are equals. In
parse_cec_param() it does not seem to matter.
I have seen that Thomas Gleixner has already committed a modified
patch which uses strcmp(), which looks good to me.

Thanks!
Nicolas