Re: [PATCH 6/8] ASoC: intel: skylake: change snprintf to scnprintf for possible overflow

[Pierre-Louis Bossart]

> > diff --git a/sound/soc/intel/skylake/skl-debug.c b/sound/soc/intel/skylake/skl-debug.c
> > index 5d7ac2ee7a3c..bb28db734fb7 100644
> > --- a/sound/soc/intel/skylake/skl-debug.c
> > +++ b/sound/soc/intel/skylake/skl-debug.c
> > @@ -43,7 +43,7 @@ static ssize_t skl_print_pins(struct skl_module_pin *m_pin, char *buf,
> >          ssize_t ret = 0;
> >
> >          for (i = 0; i < max_pin; i++)
> > -               ret += snprintf(buf + size, MOD_BUF - size,
> > +               ret += scnprintf(buf + size, MOD_BUF - size,
> >                                  "%s %d\n\tModule %d\n\tInstance %d\n\t"
> >                                  "In-used %s\n\tType %s\n"
> >                                  "\tState %d\n\tIndex %d\n",
> While working on a Coccinelle script to find more cases of this, I
> noticed that this code is buggy: it keeps overwriting the same
> position in the buf string: "buf + size" and don't take "ret" into
> account at all. This needs to be:
>
> ret += scnprintf(buf + size + ret, MOD_BUF - size - ret,

Thanks for the sighting. Indeed this looks like a bug, all other calls 
to snprintf use "ret" to modify the destination/length.

The only explanation I have for it not being noticed earlier is that 
it's possibly not used - a 5mn test on 2 machines show the loop is 
actually not run (max_pin == 0).

It'll take me a bit of time to figure out what exactly this routine is 
supposed to do, maybe we should do the cross-tree change first?

-Pierre