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

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Date:   Sun, 24 Apr 2022 01:47:35 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Larry Finger <Larry.Finger@...inger.net>,
        Phillip Potter <phil@...lpotter.co.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Straube <straube.linux@...il.com>,
        Vihas Makwana <makvihas@...il.com>
Cc:     linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Pavel Skripkin <paskripkin@...il.com>,
        Vihas Makwana <makvihas@...il.com>
Subject: Re: [PATCH] staging: r8188eu: fix a potential NULL pointer dereference

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))
> -- 
> 2.30.2
>