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

Heiko Carstens
2021-10-05T08:54:41Z

On Tue, Oct 05, 2021 at 11:18:38AM +0300, Andy Shevchenko wrote:
> 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?

Don't know. You could use strncopy+strlen+memset (with space
character). After all I'm not very convinced that the resulting code
buys us anything compared to the current variant.

> > > + 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.

I'm talking about the new code, not the old code: If "name" points to
a NUL terminated eight chararacter string, then the new code will use
snprintf to copy it 1:1 to tmp, and the subsequent string_upper() will
copy the string (upper cased) to dcss_name, now including the NUL
terminating byte, which won't fit into dcss_name.
Am I missing something here?