netdev - Re: [PATCH] Bluetooth: fix "list_add double add" in hci_conn_complete

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Date:   Wed, 2 Sep 2020 20:31:25 +0800
From:   Coiby Xu <coiby.xu@...il.com>
To:     Marcel Holtmann <marcel@...tmann.org>
Cc:     linux-bluetooth <linux-bluetooth@...r.kernel.org>,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Greg KH <gregkh@...uxfoundation.org>,
        syzkaller-bugs@...glegroups.com,
        syzbot+dd768a260f7358adbaf9@...kaller.appspotmail.com,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Bluetooth: fix "list_add double add" in
 hci_conn_complete_evt

On Mon, Aug 31, 2020 at 06:06:18PM +0200, Marcel Holtmann wrote:
>Hi Coiby,

Hi Marcel,

Thank you for reviewing this patch!

>
>> When two HCI_EV_CONN_COMPLETE event packets with status=0 of the same
>> HCI connection are received, device_add would be called twice which
>> leads to kobject_add being called twice. Thus duplicate
>> (struct hci_conn *conn)->dev.kobj.entry would be inserted into
>> (struct hci_conn *conn)->dev.kobj.kset->list.
>>
>> This issue can be fixed by checking (struct hci_conn *conn)->debugfs.
>> If it's not NULL, it means the HCI connection has been completed and we
>> won't duplicate the work as for processing the first
>> HCI_EV_CONN_COMPLETE event.
>
>do you have a btmon trace for this happening?

Please see the attachment "btmon_output" which is a plain text file.
I couldn't find a way to save traces in btsnoop format (the kernel would
panic immediately after running the re-producer before QEMU has a chance
to write the btsnoop file to the disk image).

I've also also attached a simplified re-producer rep9_min.c if it interests you.
>
>> Reported-and-tested-by: syzbot+dd768a260f7358adbaf9@...kaller.appspotmail.com
>> Link: https://syzkaller.appspot.com/bug?extid=dd768a260f7358adbaf9
>> Signed-off-by: Coiby Xu <coiby.xu@...il.com>
>> ---
>> net/bluetooth/hci_event.c | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
>> index 4b7fc430793c..1233739ce760 100644
>> --- a/net/bluetooth/hci_event.c
>> +++ b/net/bluetooth/hci_event.c
>> @@ -2605,6 +2605,11 @@ static void hci_conn_complete_evt(struct hci_dev *hdev, struct sk_buff *skb)
>> 	}
>>
>> 	if (!ev->status) {
>> +		if (conn->debugfs) {
>> +			bt_dev_err(hdev, "The connection has been completed");
>> +			goto unlock;
>> +		}
>> +
>
>And instead of doing papering over a hole, I would rather detect that the HCI event is not valid since we already received one for this connection.

To check conn->debugfs is what I think could be used to detect this
duplicate HCI event. Or you are suggesting this is not sufficient
and implement something like a state machine instead?

>
>Regards
>
>Marcel
>

--
Best regards,
Coiby

View attachment "btmon_output" of type "text/plain" (14656 bytes)

View attachment "rep9_min.c" of type "text/plain" (7471 bytes)