Re: [PATCHv5] mac80211: fix NULL pointer dereference in ieee80211_compatible_rates

["Tomas Winkler" <tomasw@gmail.com>]

On Tue, May 20, 2008 at 10:56 AM, Helmut Schaa <hschaa@suse.de> wrote:
> Fix a possible NULL pointer dereference in ieee80211_compatible_rates
> introduced in the patch "mac80211: fix association with some APs". If no bss
> is available just use all supported rates in the association request.
>
> Signed-off-by: Helmut Schaa <hschaa@suse.de>
> ---
>
> diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
> index 76ad4ed..3f7f92a 100644
> --- a/net/mac80211/mlme.c
> +++ b/net/mac80211/mlme.c
> @@ -721,7 +721,17 @@ static void ieee80211_send_assoc(struct net_device
> *dev,
>                        capab |= WLAN_CAPABILITY_PRIVACY;
>                if (bss->wmm_ie)
>                        wmm = 1;
> +
> +               /* get all rates supported by the device and the AP as
> +                * some APs don't like getting a superset of their rates
> +                * in the association request (e.g. D-Link DAP 1353 in
> +                * b-only mode) */
> +               rates_len = ieee80211_compatible_rates(bss, sband, &rates);
> +
>                ieee80211_rx_bss_put(dev, bss);
> +       } else {
> +               rates = ~0;
> +               rates_len = sband->n_bitrates;
>        }
>
>        mgmt = (struct ieee80211_mgmt *) skb_put(skb, 24);
> @@ -752,10 +762,7 @@ static void ieee80211_send_assoc(struct net_device
> *dev,
>        *pos++ = ifsta->ssid_len;
>        memcpy(pos, ifsta->ssid, ifsta->ssid_len);
>
> -       /* all supported rates should be added here but some APs
> -        * (e.g. D-Link DAP 1353 in b-only mode) don't like that
> -        * Therefore only add rates the AP supports */
> -       rates_len = ieee80211_compatible_rates(bss, sband, &rates);
> +       /* add all rates which were marked to be used above */
>        supp_rates_len = rates_len;
>        if (supp_rates_len > 8)
>                supp_rates_len = 8;
>
>

I found one  ieee80211_rx_bss_{get,put} imbalance   in
ieee80211_sta_join_ibss function
That may cause this problem yet it doesn't look like this is the case.
ieee80211_sta_join_ibss
calls ieee80211_rx_bss_put on 'bss' that it receives as an argument
Keep searching.

I suggest to insert at least some WARN_ON(1) for the else case.

Tomas