linux-kernel - Re: [PATCH] Bluetooth: skip invalid hci_sync_conn_complete

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Date:   Thu, 22 Jul 2021 16:39:12 +0200
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
Cc:     Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-bluetooth <linux-bluetooth@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        skhan@...uxfoundation.org, gregkh@...uxfoundation.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+66264bf2fd0476be7e6c@...kaller.appspotmail.com
Subject: Re: [PATCH] Bluetooth: skip invalid hci_sync_conn_complete_evt

Hi Desmond,

> Syzbot reported a corrupted list in kobject_add_internal [1]. This
> happens when multiple HCI_EV_SYNC_CONN_COMPLETE event packets with
> status 0 are sent for the same HCI connection. This causes us to
> register the device more than once which corrupts the kset list.

and that is actually forbidden by the spec. So we need to complain loudly that such a device is misbehaving.

> To fix this, in hci_sync_conn_complete_evt, we check whether we're
> trying to process the same HCI_EV_SYNC_CONN_COMPLETE event multiple
> times for one connection. If that's the case, the event is invalid, so
> we skip further processing and exit.
> 
> Link: https://syzkaller.appspot.com/bug?extid=66264bf2fd0476be7e6c [1]
> Reported-by: syzbot+66264bf2fd0476be7e6c@...kaller.appspotmail.com
> Tested-by: syzbot+66264bf2fd0476be7e6c@...kaller.appspotmail.com
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
> ---
> net/bluetooth/hci_event.c | 2 ++
> 1 file changed, 2 insertions(+)
> 
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index 016b2999f219..091a92338492 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -4373,6 +4373,8 @@ static void hci_sync_conn_complete_evt(struct hci_dev *hdev,
> 
> 	switch (ev->status) {
> 	case 0x00:
> +		if (conn->state == BT_CONNECTED)
> +			goto unlock;  /* Already connected, event not valid */

The comment has go above and be a lot more details since this is not expected behavior from valid hardware and we should add a bt_dev_err as well.

> 		conn->handle = __le16_to_cpu(ev->handle);
> 		conn->state  = BT_CONNECTED;
> 		conn->type   = ev->link_type;

Regards

Marcel