linux-kernel - Re: [PATCH v1 1/1] s390: Use string_upper() instead of open coded variant

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Message-ID: <YVwKXn1Nqwk+Ahsx@smile.fi.intel.com>
Date:   Tue, 5 Oct 2021 11:18:38 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [PATCH v1 1/1] s390: Use string_upper() instead of open coded
 variant

On Mon, Oct 04, 2021 at 10:31:46PM +0200, Heiko Carstens wrote:
> On Fri, Oct 01, 2021 at 04:02:01PM +0300, Andy Shevchenko wrote:

...

> > +	/* Segment name is limited by 8 characters + NUL */
> > +	char tmp[8 + 1];
> >  	int i;
> >  
> > -	for (i = 0; i < 8; i++) {
> > -		if (name[i] == '\0')
> > -			break;
> > -		dcss_name[i] = toupper(name[i]);
> > -	}
> > -	for (; i < 8; i++)
> > -		dcss_name[i] = ' ';
> > +	/*
> > +	 * This snprintf() call does two things:
> > +	 * - makes a NUL-terminated copy of the input string
> > +	 * - pads it with spaces
> > +	 */
> > +	snprintf(tmp, sizeof(tmp), "%s        ", name);
> 
> I can't say I like code where I have to count spaces in order to
> verify if the code is actually correct.

I understand your point, but have any idea how to make it differently
and not ugly at the same time?

> > +	string_upper(dcss_name, tmp);

...

> >  static struct dcss_segment *
> >  segment_by_name (char *name)
> >  {
> > -	char dcss_name[9];
> > +	char dcss_name[8];
> 
> string_upper will copy the terminating NUL-byte. By reducing the size
> of dcss_name to 8 bytes this will result in stack corruption.

Nope. Even in the original code this additional byte is left unused.

-- 
With Best Regards,
Andy Shevchenko