linux-kernel - Re: [PATCH 3/3] staging: r8188eu: fix null check in _rtw_free_mlme

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Message-ID: <CAH1kMwTT7kEB5O6ZvCWEJk3RGzkRek_fzaNPUnUpFFKq_fhGvQ@mail.gmail.com>
Date:   Mon, 25 Apr 2022 23:25:32 +0530
From:   Vihas Makwana <makvihas@...il.com>
To:     Pavel Skripkin <paskripkin@...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>
Subject: Re: [PATCH 3/3] staging: r8188eu: fix null check in _rtw_free_mlme_priv

On Mon, Apr 25, 2022 at 12:30 AM Pavel Skripkin <paskripkin@...il.com> wrote:
>
> Hi Vihas,
>
> On 4/24/22 19:31, Vihas Makwana wrote:
> > There's a NULL check on pmlmepriv in rtw_mlme.c:112 which makes no sense
> > as rtw_free_mlme_priv_ie_data() dereferences it unconditionally and it
> > would have already crashed at this point.
> > Fix this by moving rtw_free_mlme_priv_ie_data() inside the check.
> >
> > Signed-off-by: Vihas Makwana <makvihas@...il.com>
>
> That's good catch, but looks like the check is just redundant
>
> This function is called only from it's wrapper called
> rtw_free_mlme_priv() and rtw_free_mlme_priv() is called from 2 places:
>
> 4 drivers/staging/r8188eu/os_dep/os_intfs.c|531 col 2|
> rtw_free_mlme_priv(&padapter->mlmepriv);
> 5 drivers/staging/r8188eu/os_dep/os_intfs.c|579 col 2|
> rtw_free_mlme_priv(&padapter->mlmepriv);
>
> _Very_ unlikely that `&padapter->mlmepriv` expression will become NULL.
>
So I guess either we should remove the check or mark it with the
`unlikely()` macro.
>
> > ---
> >   drivers/staging/r8188eu/core/rtw_mlme.c | 8 +++-----
> >   1 file changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/staging/r8188eu/core/rtw_mlme.c b/drivers/staging/r8188eu/core/rtw_mlme.c
> > index 081c02417..87c754462 100644
> > --- a/drivers/staging/r8188eu/core/rtw_mlme.c
> > +++ b/drivers/staging/r8188eu/core/rtw_mlme.c
> > @@ -109,12 +109,10 @@ void rtw_free_mlme_priv_ie_data(struct mlme_priv *pmlmepriv)
> >
> >   void _rtw_free_mlme_priv(struct mlme_priv *pmlmepriv)
> >   {
> > -
> > -     rtw_free_mlme_priv_ie_data(pmlmepriv);
> > -
> > -     if (pmlmepriv)
> > +     if (pmlmepriv) {
> > +             rtw_free_mlme_priv_ie_data(pmlmepriv);
> >               vfree(pmlmepriv->free_bss_buf);
> > -
> > +     }
> >   }
> >
> >   struct      wlan_network *_rtw_alloc_network(struct mlme_priv *pmlmepriv)/* _queue *free_queue) */
>
>
>
>
> With regards,
> Pavel Skripkin



-- 
Thanks,
Vihas