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Subject: Re: [PATCH 1/2] Bluetooth: call sock_hold earlier in sco_conn_del
To:     Marcel Holtmann <marcel@holtmann.org>
Cc:     Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        linux-bluetooth <linux-bluetooth@vger.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        eric.dumazet@gmail.com
References: <20210903031306.78292-1-desmondcheongzx@gmail.com>
 <20210903031306.78292-2-desmondcheongzx@gmail.com>
 <7AEB2618-111A-45F4-8C00-CF40FCBE92EC@holtmann.org>
From:   Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Message-ID: <1203215b-13bf-ce0c-ef23-5664544607a1@gmail.com>
Date:   Mon, 4 Oct 2021 14:12:07 -0400
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Hi Marcel,

On 10/9/21 3:36 am, Marcel Holtmann wrote:
> Hi Desmond,
> 
>> In sco_conn_del, conn->sk is read while holding on to the
>> sco_conn.lock to avoid races with a socket that could be released
>> concurrently.
>>
>> However, in between unlocking sco_conn.lock and calling sock_hold,
>> it's possible for the socket to be freed, which would cause a
>> use-after-free write when sock_hold is finally called.
>>
>> To fix this, the reference count of the socket should be increased
>> while the sco_conn.lock is still held.
>>
>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
>> ---
>> net/bluetooth/sco.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
>> index b62c91c627e2..4a057f99b60a 100644
>> --- a/net/bluetooth/sco.c
>> +++ b/net/bluetooth/sco.c
>> @@ -187,10 +187,11 @@ static void sco_conn_del(struct hci_conn *hcon, int err)
>> 	/* Kill socket */
>> 	sco_conn_lock(conn);
>> 	sk = conn->sk;
> 
> please add a comment here on why we are doing it.
> 

So sorry for the very delayed response. I was looking through old email 
threads to check if my recently resent patch was still necessary, and 
just realized I missed this email.

This patch was merged into the bluetooth-next tree before your feedback 
came in. Would you still like me to write a separate patch to add the 
requested comment?

Best wishes,
Desmond

>> +	if (sk)
>> +		sock_hold(sk);
>> 	sco_conn_unlock(conn);
>>
>> 	if (sk) {
>> -		sock_hold(sk);
>> 		lock_sock(sk);
>> 		sco_sock_clear_timer(sk);
>> 		sco_chan_del(sk, err);
> 
> Regards
> 
> Marcel
>