linux-kernel - Re: [PATCH] staging: r8188eu: fix a potential NULL pointer dereference

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Date:   Sun, 24 Apr 2022 14:57:45 +0530
From:   Vihas Makwana <makvihas@...il.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Larry Finger <Larry.Finger@...inger.net>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Straube <straube.linux@...il.com>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Pavel Skripkin <paskripkin@...il.com>
Subject: Re: [PATCH] staging: r8188eu: fix a potential NULL pointer dereference

On Sun, Apr 24, 2022 at 5:17 AM Fabio M. De Francesco
<fmdefrancesco@...il.com> wrote:
>
> On sabato 23 aprile 2022 20:47:48 CEST Vihas Makwana wrote:
> > recvframe_chk_defrag() performs a NULL check on psta, but if that check
> > fails then it dereferences it, which it shouldn't do as psta is NULL.
> >
> > Set pdefrag_q to NULL if above check fails and let the code after it
> handle
> > that case.
> >
> > Fixes: 1cc18a22b96b ("staging: r8188eu: Add files for new driver - part
> 5")
> > Signed-off-by: Vihas Makwana <makvihas@...il.com>
> > ---
> >  drivers/staging/r8188eu/core/rtw_recv.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/r8188eu/core/rtw_recv.c b/drivers/staging/
> r8188eu/core/rtw_recv.c
> > index c1005ddaa..db54bceff 100644
> > --- a/drivers/staging/r8188eu/core/rtw_recv.c
> > +++ b/drivers/staging/r8188eu/core/rtw_recv.c
> > @@ -1244,7 +1244,7 @@ struct recv_frame *recvframe_chk_defrag(struct
> adapter *padapter, struct recv_fr
> >                       pdefrag_q = NULL;
> >               }
> >       } else {
> > -             pdefrag_q = &psta->sta_recvpriv.defrag_q;
> > +             pdefrag_q = NULL;
>
> Hi Vihas,
>
> To me the code looks like this...
>
>         struct sta_info *psta;
>         ...
>         psta = rtw_get_stainfo(pstapriv, psta_addr);
>         /* The code is about to test if "psta" is a valid pointer */
>         if (!psta) {
>                 /* "psta" is NULL */
>                 ...
>         } else {
>                 /* "psta" is not NULL */
>                 ...
>
> >       }
> >
>
> Also, even if "psta" were NULL (but it isn't), your change would still be
> no good.
>
> Please be very careful with these types of changes next time :)
>
> Thanks,
>
> Fabio M. De Francesco
>
> >       if ((ismfrag == 0) && (fragnum == 0))
> > --
Oh yea, sorry about this. I don't know how I missed this.
Thanks for clarification Fabio. Will take care next time.


-- 
Thanks,
Vihas