Re: [PATCH] arm64/mm: Reject invalid NUMA option

Steven Rostedt
2020-04-28T02:59:53Z

On Mon, 27 Apr 2020 22:54:06 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 28 Apr 2020 10:59:14 +1000
> Gavin Shan <gshan@redhat.com> wrote:
>
> > Hi Mark,
> >
> > On 4/24/20 8:11 PM, Mark Rutland wrote:
> > > [Adding Steve, who added str_has_prefix()]
> > >
> > > On Fri, Apr 24, 2020 at 02:53:14PM +1000, Gavin Shan wrote:
> > >> The NUMA option is parsed by str_has_prefix() and the invalid option
> > >> like "numa=o" can be regarded as "numa=off" wrongly.
> > >
> > > Are you certain that can pass? If that can happen, str_has_prefix() is
> > > misnamed and does not seem to do what its kerneldoc says it does, as
> > > "off" is not a prefix of "o".
> > >
> >
> > Yes, It's possible. str_has_prefix() depends on strncmp(). In this particular
> > case, it's equal to the snippet of code as below: strncmp() returns zero.
> > str_has_prefix() returns 3.
>
> Wait! strncmp("o", "off", 3) returns zero?
>
> That to me looks like a bug!
>
> This means str_has_prefix() is broken in other areas as well.
>
>
> >
> > int strncmp(const char *cs, const char *ct, size_t count)
> > {
> > unsigned char c1, c2;
> >
> > while (count) {
> > c1 = *cs++;
> > c2 = *ct++;
> > if (c1 != c2)
> > return c1 < c2 ? -1 : 1;
> > if (!c1) /* break after first character is compared */
>
> Crap! That is totally wrong!

Looking at this again, it's not wrong. But how did we get here if c2 isn't
zero as well?

-- Steve