Re: [PATCH 1/1] staging: rtl8723bs: make memcmp() calls consistent

[Hans de Goede]

Hi,

On 13-12-17 16:12, Rasmus Villemoes wrote:
> On 2017-12-13 15:49, Hans de Goede wrote:
> > Hi,
> >
> > On 13-12-17 12:47, Greg Kroah-Hartman wrote:
> > > On Sun, Dec 10, 2017 at 08:35:12PM +0100, Nicolas Iooss wrote:
> > > > rtw_pm_set() uses memcmp() with 5-chars strings and a length of 4 when
> > > > parsing extra, and then parses extra+4 as an int:
> > > >
> > > >       if (!memcmp(extra, "lps =", 4)) {
> > > >           sscanf(extra+4, "%u", &mode);
> > > >       /* ... */
> > > >       } else if (!memcmp(extra, "ips =", 4)) {
> > > >           sscanf(extra+4, "%u", &mode);
> > > >
> > > > The space between the key ("lps" and "ips") and the equal sign seems
> > > > suspicious. Remove it in order to make the calls to memcmp() consistent.
> > >
> > > But you now just changing the parsing logic.  What broke because of
> > > this?  Did you test this codepath with your patch?
> > >
> > > I'm not disagreeing that this code seems really odd, but it must be
> > > working as-is for someone, to change this logic will break their system
> > > :(
> >
> > I don't think this code can work actually, for the memcmp to
> > match the extra argument must start with e.g. : "lps ="
>
> No, the extra argument just has to start with "lps ", so something like
> "lps 1234" would "work". The memcmp call could just as well use "lps ".

Ah yes, you're right, it only compares the first 4 chars.

> but then mode
> > gets read as: sscanf(extra+4, "%u", &mode);, with extra + 4
> > pointing at the "=" in the extra arg, so sscanf will stop right
> > away and store 0 in mode.
>
> See above, we don't know there's a "=" at extra+4. But in any case,
> I don't think sscanf stores anything if there are no digits (and then it
> would return 0 since no specifiers matched - the code also lacks a check
> of the sscanf return value). But mode is initialized, so it's not going
> to use some stack garbage.
>
> All in all, some cleanup seems warranted. Why not just do a sscanf("lps
> %u", ...) call and properly check the return value of that? With
> whatever prefix string one thinks would be most appropriate.
>
> > So this is for a private extension to the iw interface. I think that
> > as part of the cleanup of this driver in staging we should just
> > remove all private extensions, which will nicely fix the broken
> > function by simply removing it :)
>
> Yeah, that would also work...

Either one is fine with me.

Regards,

Hans