Re: [PATCH 2/2] cfg80211: wext: Reject malformed SSID elements

[Kees Cook <keescook@chromium.org>]

On Fri, Oct 04, 2019 at 10:51:32AM +0100, Will Deacon wrote:
> Ensure the SSID element is bounds-checked prior to invoking memcpy()
> with its length field.
> 
> Cc: <stable@vger.kernel.org>
> Cc: Johannes Berg <johannes@sipsolutions.net>
> Cc: Kees Cook <keescook@chromium.org>
> Reported-by: Nicolas Waisman <nico@semmle.com>
> Signed-off-by: Will Deacon <will@kernel.org>

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

-Kees

> ---
>  net/wireless/wext-sme.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/net/wireless/wext-sme.c b/net/wireless/wext-sme.c
> index c67d7a82ab13..3fd2cc7fc36a 100644
> --- a/net/wireless/wext-sme.c
> +++ b/net/wireless/wext-sme.c
> @@ -201,6 +201,7 @@ int cfg80211_mgd_wext_giwessid(struct net_device *dev,
>  			       struct iw_request_info *info,
>  			       struct iw_point *data, char *ssid)
>  {
> +	int ret = 0;
>  	struct wireless_dev *wdev = dev->ieee80211_ptr;
>  
>  	/* call only for station! */
> @@ -219,7 +220,10 @@ int cfg80211_mgd_wext_giwessid(struct net_device *dev,
>  		if (ie) {
>  			data->flags = 1;
>  			data->length = ie[1];
> -			memcpy(ssid, ie + 2, data->length);
> +			if (data->length > IW_ESSID_MAX_SIZE)
> +				ret = -EINVAL;
> +			else
> +				memcpy(ssid, ie + 2, data->length);
>  		}
>  		rcu_read_unlock();
>  	} else if (wdev->wext.connect.ssid && wdev->wext.connect.ssid_len) {
> @@ -229,7 +233,7 @@ int cfg80211_mgd_wext_giwessid(struct net_device *dev,
>  	}
>  	wdev_unlock(wdev);
>  
> -	return 0;
> +	return ret;
>  }
>  
>  int cfg80211_mgd_wext_siwap(struct net_device *dev,
> -- 
> 2.23.0.581.g78d2f28ef7-goog
> 

-- 
Kees Cook