linux-kernel - Re: [PATCH 2/2] net: mac80211: Fix possible null-pointer dereferences in ieee80211_xmit_fast

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Message-ID: <91f918911b7a33c84d7a620e75a1d8155a239237.camel@sipsolutions.net>
Date:   Wed, 24 Jul 2019 14:39:16 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, davem@...emloft.net
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] net: mac80211: Fix possible null-pointer
 dereferences in ieee80211_xmit_fast_finish()

On Wed, 2019-07-24 at 20:36 +0800, Jia-Ju Bai wrote:
> In ieee80211_xmit_fast_finish(), there is an if statement on line 3356
> to check whether key is NULL:
>     if (key)
> 
> When key is NULL, it is used on line 3388:
>     switch (key->conf.cipher)
> and line 3393:
>     pn = atomic64_inc_return(&key->conf.tx_pn);
> and line 3396:
>     crypto_hdr[3] = 0x20 | (key->conf.keyidx << 6);
> 
> Thus, possible null-pointer dereferences may occur.

No, this cannot happen, because pn_offs can only be non-zero when there
is a key. Maybe we should pass the fast_tx pointer instead of the
pn_offs/key from it, but the two are coupled.

johannes