Re: [PATCH][next] rtw89: Fix potential dereference of the null pointer sta

Dan Carpenter
2021-11-03T10:22:03Z

On Wed, Nov 03, 2021 at 12:36:17AM +0000, Pkshih wrote:

> > > > diff --git a/drivers/net/wireless/realtek/rtw89/core.c
> > > > b/drivers/net/wireless/realtek/rtw89/core.c
> > > > index 06fb6e5b1b37..26f52a25f545 100644
> > > > --- a/drivers/net/wireless/realtek/rtw89/core.c
> > > > +++ b/drivers/net/wireless/realtek/rtw89/core.c
> > > > @@ -1534,9 +1534,14 @@ static bool rtw89_core_txq_agg_wait(struct rtw89_dev *rtwdev,
> > > > {
> > > > struct rtw89_txq *rtwtxq = (struct rtw89_txq *)txq->drv_priv;
> > > > struct ieee80211_sta *sta = txq->sta;
> > > > - struct rtw89_sta *rtwsta = (struct rtw89_sta *)sta->drv_priv;
> > >
> > > 'sta->drv_priv' is only a pointer, we don't really dereference the
> > > data right here, so I think this is safe. More, compiler can optimize
> > > this instruction that reorder it to the place just right before using.
> > > So, it seems like a false alarm.
> >
> > The warning is about "sta" not "sta->priv". It's not a false positive.
> >
> > I have heard discussions about compilers trying to work around these
> > bugs by re-ordering the code. Is that an option in GCC? It's not
> > something we should rely on, but I'm just curious if it exists in
> > released versions.
> >
>
> I say GCC does "reorder" the code, because the object codes of following
> two codes are identical with default or -Os ccflags.

Huh... That's cool. GCC doesn't re-order it for me, but I'm on GCC 8
so maybe it will work when I get to a more modern version.

regards,
dan carpenter