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

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Message-ID: <CAGRGNgVF_s1ux9TjL6TqUDF=NB9e-XS0CQvowEGV=9Vj5r9Osg@mail.gmail.com>
Date:	Mon, 7 Jan 2013 14:03:10 +1100
From:	Julian Calaby <julian.calaby@...il.com>
To:	Lennert Buytenhek <buytenh@...tstofly.org>
Cc:	Nickolai Zeldovich <nickolai@...il.mit.edu>,
	"John W. Linville" <linville@...driver.com>,
	linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/net/wireless/mwl8k.c: avoid use-after-free

Hi Lennert,

On Mon, Jan 7, 2013 at 1:48 PM, Lennert Buytenhek
<buytenh@...tstofly.org> 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@...il.com
Profile: http://www.google.com/profiles/julian.calaby/
.Plan: http://sites.google.com/site/juliancalaby/
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