Re: [PATCH] mac80211: fix invalid band deref building preq IEs

[Johannes Berg <johannes@sipsolutions.net>]

On Mon, 2012-07-09 at 19:49 +0300, Arik Nemtsov wrote:
> The function building probe-request IEs does not validate the band is
> supported before dereferencing it. This can result in a panic when
> all bands are traversed, as done during sched-scan start.
> 
> Warn when this happens and return an empty probe request. Also fix
> sched-scan to not waste memory on unsupported bands.
> 
> Signed-off-by: Arik Nemtsov <arik@wizery.com>
> ---
> This is not cc stable since the panic only started happening once
> the 60Ghz band was added. Apparently all sched-scan drivers supported
> all possible bands until then.
> 
> 
>  net/mac80211/scan.c |    3 +++
>  net/mac80211/util.c |    2 ++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
> index 379f178..1ff04f6 100644
> --- a/net/mac80211/scan.c
> +++ b/net/mac80211/scan.c
> @@ -928,6 +928,9 @@ int ieee80211_request_sched_scan_start(struct ieee80211_sub_if_data *sdata,
>  	}
>  
>  	for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
> +		if (!local->hw.wiphy->bands[i])
> +			continue;
> +
>  		local->sched_scan_ies.ie[i] = kzalloc(2 +
>  						      IEEE80211_MAX_SSID_LEN +
>  						      local->scan_ies_len +
> diff --git a/net/mac80211/util.c b/net/mac80211/util.c
> index 64493a7..503412a 100644
> --- a/net/mac80211/util.c
> +++ b/net/mac80211/util.c
> @@ -999,6 +999,8 @@ int ieee80211_build_preq_ies(struct ieee80211_local *local, u8 *buffer,
>  	int ext_rates_len;
>  
>  	sband = local->hw.wiphy->bands[band];
> +	if (!WARN_ON_ONCE(sband))
> +		return 0;

That's not right :-)

johannes