linux-kernel - Re: [PATCH][next] wireless: wext-spy: Fix out-of-bounds warning

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Date:   Wed, 21 Apr 2021 17:22:11 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Johannes Berg <johannes@...solutions.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] wireless: wext-spy: Fix out-of-bounds warning

On Wed, Apr 21, 2021 at 06:43:37PM -0500, Gustavo A. R. Silva wrote:
> Fix the following out-of-bounds warning:
> 
> net/wireless/wext-spy.c:178:2: warning: 'memcpy' offset [25, 28] from the object at 'threshold' is out of the bounds of referenced subobject 'low' with type 'struct iw_quality' at offset 20 [-Warray-bounds]
> 
> The problem is that the original code is trying to copy data into a
> couple of struct members adjacent to each other in a single call to
> memcpy(). This causes a legitimate compiler warning because memcpy()
> overruns the length of &threshold.low and &spydata->spy_thr_low. As
> these are just a couple of members, fix this by copying each one of
> them in separate calls to memcpy().
> 
> Also, while there, use sizeof(threshold.qual) instead of
> sizeof(struct iw_quality)) in another call to memcpy()
> above.
> 
> This helps with the ongoing efforts to globally enable -Warray-bounds
> and get us closer to being able to tighten the FORTIFY_SOURCE routines
> on memcpy().
> 
> Link: https://github.com/KSPP/linux/issues/109
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks!

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  net/wireless/wext-spy.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/net/wireless/wext-spy.c b/net/wireless/wext-spy.c
> index 33bef22e44e9..bb2de7c6bee4 100644
> --- a/net/wireless/wext-spy.c
> +++ b/net/wireless/wext-spy.c
> @@ -120,8 +120,8 @@ int iw_handler_set_thrspy(struct net_device *	dev,
>  		return -EOPNOTSUPP;
>  
>  	/* Just do it */
> -	memcpy(&(spydata->spy_thr_low), &(threshold->low),
> -	       2 * sizeof(struct iw_quality));
> +	memcpy(&spydata->spy_thr_low, &threshold->low, sizeof(threshold->low));
> +	memcpy(&spydata->spy_thr_high, &threshold->high, sizeof(threshold->high));
>  
>  	/* Clear flag */
>  	memset(spydata->spy_thr_under, '\0', sizeof(spydata->spy_thr_under));
> @@ -173,10 +173,10 @@ static void iw_send_thrspy_event(struct net_device *	dev,
>  	memcpy(threshold.addr.sa_data, address, ETH_ALEN);
>  	threshold.addr.sa_family = ARPHRD_ETHER;
>  	/* Copy stats */
> -	memcpy(&(threshold.qual), wstats, sizeof(struct iw_quality));
> +	memcpy(&threshold.qual, wstats, sizeof(threshold.qual));
>  	/* Copy also thresholds */
> -	memcpy(&(threshold.low), &(spydata->spy_thr_low),
> -	       2 * sizeof(struct iw_quality));
> +	memcpy(&threshold.low, &spydata->spy_thr_low, sizeof(threshold.low));
> +	memcpy(&threshold.high, &spydata->spy_thr_high, sizeof(threshold.high));
>  
>  	/* Send event to user space */
>  	wireless_send_event(dev, SIOCGIWTHRSPY, &wrqu, (char *) &threshold);
> -- 
> 2.27.0
> 

-- 
Kees Cook