Re: [PATCH] drivers/net/wireless/mwl8k.c: avoid use-after-free

[Julian Calaby]

Hi Lennert,

On Mon, Jan 7, 2013 at 1:48 PM, Lennert Buytenhek
<buytenh@xxxxxxxxxxxxxx> wrote:
> On Sun, Jan 06, 2013 at 08:27:22PM -0500, Nickolai Zeldovich wrote:
>
>> Do not dereference p->station_id after kfree(cmd) because p
>> points into the cmd data structure.
>
> Good catch, but the patch would be better titled "mwl8k.c: avoid
> having a working driver", as the station_id return code _is_ needed
> by the caller in case of success.

Are you sure?

>> diff --git a/drivers/net/wireless/mwl8k.c b/drivers/net/wireless/mwl8k.c
>> index f221b95..83564d3 100644
>> --- a/drivers/net/wireless/mwl8k.c
>> +++ b/drivers/net/wireless/mwl8k.c
>> @@ -4250,9 +4250,11 @@ static int mwl8k_cmd_update_stadb_add(struct ieee80211_hw *hw,
>>       p->amsdu_enabled = 0;
>>
>>       rc = mwl8k_post_cmd(hw, &cmd->header);
>> +     if (!rc)
>> +             rc = p->station_id;
>>       kfree(cmd);
>>
>> -     return rc ? rc : p->station_id;

If I'm reading this right, the removed line is equivalent to:

if( rc )
    return rc;
else
    return p->station_id;

which is equivalent to:

if( !rc )
    rc = p->station_id;

return rc;


Thanks,

-- 
Julian Calaby

Email: julian.calaby@xxxxxxxxx
Profile: http://www.google.com/profiles/julian.calaby/
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