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Subject: Re: [PATCH 1/2] Bluetooth: call sock_hold earlier in sco_conn_del
From:   Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <20210903031306.78292-2-desmondcheongzx@gmail.com>
Date:   Fri, 10 Sep 2021 09:36:25 +0200
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
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Message-Id: <7AEB2618-111A-45F4-8C00-CF40FCBE92EC@holtmann.org>
References: <20210903031306.78292-1-desmondcheongzx@gmail.com>
 <20210903031306.78292-2-desmondcheongzx@gmail.com>
To:     Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Precedence: bulk

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.

> +	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