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

[Arik Nemtsov <arik@xxxxxxxxxx>]

On Mon, Jul 9, 2012 at 7:54 PM, Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
>> ---
>> 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 :-)

heh. yea I guess I didn't test it with the WARN_ON :)
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