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

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Date:   Mon, 25 Apr 2022 11:22:44 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Vihas Makwana <makvihas@...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,
        Pavel Skripkin <paskripkin@...il.com>
Subject: Re: [PATCH] staging: r8188eu: fix a potential NULL pointer
 dereference

On Sun, Apr 24, 2022 at 12:17:48AM +0530, 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;

What?  "psta" is valid pointer on the else path.

(Also this isn't really a dereference, this is just pointer math.  It's
taking the address.  The Oops would happen later if psta were NULL.)

regards,
dan carpenter