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

[Pkshih]

> -----Original Message-----
> From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Sent: Wednesday, November 3, 2021 6:21 PM
> To: Pkshih <pkshih@xxxxxxxxxxx>
> Cc: Colin King <colin.king@xxxxxxxxxxxxx>; Kalle Valo <kvalo@xxxxxxxxxxxxxx>; David S . Miller
> <davem@xxxxxxxxxxxxx>; Jakub Kicinski <kuba@xxxxxxxxxx>; linux-wireless@xxxxxxxxxxxxxxx;
> netdev@xxxxxxxxxxxxxxx; kernel-janitors@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH][next] rtw89: Fix potential dereference of the null pointer sta
> 
> 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.
> 

My GCC is 9.3.0. 
But, I don't try other versions.

--
Ping-Ke