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

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Message-ID: <2e4fa41d-cd06-75e4-17ac-120127fe9b2a@gmail.com>
Date:   Sun, 24 Apr 2022 22:00:10 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     Vihas Makwana <makvihas@...il.com>,
        Larry Finger <Larry.Finger@...inger.net>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Straube <straube.linux@...il.com>
Cc:     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

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.


> ---
>   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