Re: [PATCH] wifi: wireless: fix more UBSAN noise in cfg80211_conn_scan()

[Johannes Berg <johannes@sipsolutions.net>]

Hmm.

On Tue, 2024-07-16 at 20:40 +0300, Dmitry Antipov wrote:
> diff --git a/net/wireless/sme.c b/net/wireless/sme.c
> index a8ad55f11133..f5da45331847 100644
> --- a/net/wireless/sme.c
> +++ b/net/wireless/sme.c
> @@ -77,12 +77,16 @@ static int cfg80211_conn_scan(struct wireless_dev *wdev)
>  	else
>  		n_channels = ieee80211_get_num_supported_channels(wdev->wiphy);
>  
> -	request = kzalloc(sizeof(*request) + sizeof(request->ssids[0]) +
> -			  sizeof(request->channels[0]) * n_channels,
> -			  GFP_KERNEL);
> +	request = kzalloc(struct_size(request, channels, n_channels) +
> +			  sizeof(request->ssids[0]), GFP_KERNEL);

That makes sense, sure.

>  	if (!request)
>  		return -ENOMEM;
>  
> +	/* None of the channels are actually set
> +	 * up but let UBSAN know the boundaries.
> +	 */
> +	request->n_channels = n_channels;

Also makes sense, so we tell it how many we allocated early.

Note netdev we dropped the special comment style requirement, so
wouldn't mind

 /*
  * None of ...
  * ...
  */

here either.

> +
>  	if (wdev->conn->params.channel) {
>  		enum nl80211_band band = wdev->conn->params.channel->band;
>  		struct ieee80211_supported_band *sband =
> @@ -112,9 +116,9 @@ static int cfg80211_conn_scan(struct wireless_dev *wdev)
>  			}
>  			request->rates[band] = (1 << bands->n_bitrates) - 1;
>  		}
> -		n_channels = i;
> +		request->n_channels = i;

So this tells it how many were actually used, in this branch, makes
sense.

Functionally, all of this seems OK.

However,

>  	request->ssids = (void *)&request->channels[n_channels];

is this not checked? I mean, if you have n_channels=5 and then take
&channels[5] I can see how that makes sense, but arguably the compiler
might complain if you have &channels[10] for an array you told it has 5
entries?

johannes