linux-kernel - Re: [PATCH] Bluetooth: L2CAP: fix an illegal state transition from BT

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Date:   Mon, 26 Sep 2022 14:33:30 -0700
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     Sungwoo Kim <iam@...g-woo.kim>
Cc:     syzkaller@...glegroups.com, Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: L2CAP: fix an illegal state transition from BT_DISCONN

Hi Kim,

On Mon, Sep 26, 2022 at 1:47 PM Sungwoo Kim <iam@...g-woo.kim> wrote:
>
> Prevent an illegal state transition from BT_DISCONN to BT_CONFIG.
> L2CAP_CONN_RSP and L2CAP_CREATE_CHAN_RSP events should be ignored
> for BT_DISCONN state according to the Bluetooth Core v5.3 p.1096.
> It is found by BTFuzz, a modified version of syzkaller.
>
> Signed-off-by: Sungwoo Kim <iam@...g-woo.kim>
> ---
>  net/bluetooth/l2cap_core.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 2c9de67da..a15d64b13 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -4307,6 +4307,9 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
>                 }
>         }

Perhaps it would be better to switch to use l2cap_get_chan_by_scid and
l2cap_get_chan_by_ident, since I suspect this is caused by the socket
being terminated while the response is in course so the chan reference
is already 0 thus why l2cap_chan_hold_unless_zero is probably
preferable instead of checking the state directly.

> +       if (chan->state == BT_DISCONN)
> +               goto unlock;
> +
>         err = 0;
>
>         l2cap_chan_lock(chan);
> --
> 2.25.1
>


-- 
Luiz Augusto von Dentz