linux-kernel - Re: [RFC PATCH] Bluetooth: hci_event: Ignore multiple conn complete events

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Date:   Sat, 22 Jan 2022 00:18:01 +0100
From:   Sönke Huster <soenke.huster@...oes.de>
To:     Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] Bluetooth: hci_event: Ignore multiple conn complete
 events

Hi Luiz,

On 21.01.22 22:31, Luiz Augusto von Dentz wrote:
> Hi Sönke,
> 
> On Fri, Jan 21, 2022 at 10:22 AM Sönke Huster <soenke.huster@...oes.de> wrote:
>>
>> I just noticed that just checking for handle does not work, as obviously 0x0 could also be a handle value and therefore it can't be distinguished, whether it is not set yet or it is 0x0.
> 
> Yep, we should probably check its state, check for state != BT_OPEN
> since that is what hci_conn_add initialize the state.
> 

I thought there are more valid connection states for the first HCI_CONNECTION_COMPLETE event, as it also occurs e.g. after an HCI_Create_Connection command, see Core 5.3 p.2170:
> This event also indicates to the Host which issued the HCI_Create_Connection, HCI_Accept_-
> Connection_Request, or HCI_Reject_Connection_Request command, and
> then received an HCI_Command_Status event, if the issued command failed or
> was successful.

For example in hci_conn.c hci_acl_create_connection (which triggers a HCI_Create_Connection command as far as I understand), the state of the connection is changed to BT_CONNECT or BT_CONNECT2.
But as I am quite new in the (Linux) Bluetooth world, I might have a wrong understanding of that.

>> On 21.01.22 18:36, Soenke Huster wrote:
>>> When a HCI_CONNECTION_COMPLETE event is received multiple times
>>> for the same handle, the device is registered multiple times which leads
>>> to memory corruptions. Therefore, consequent events for a single
>>> connection are ignored.
>>>
>>> The conn->state can hold different values so conn->handle is
>>> checked to detect whether a connection is already set up.
>>>
>>> Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=215497
>>> Signed-off-by: Soenke Huster <soenke.huster@...oes.de>
>>> ---
>>> This fixes the referenced bug and several use-after-free issues I discovered.
>>> I tagged it as RFC, as I am not 100% sure if checking the existence of the
>>> handle is the correct approach, but to the best of my knowledge it must be
>>> set for the first time in this function for valid connections of this event,
>>> therefore it should be fine.
>>>
>>> net/bluetooth/hci_event.c | 11 +++++++++++
>>>  1 file changed, 11 insertions(+)
>>>
>>> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
>>> index 681c623aa380..71ccb12c928d 100644
>>> --- a/net/bluetooth/hci_event.c
>>> +++ b/net/bluetooth/hci_event.c
>>> @@ -3106,6 +3106,17 @@ static void hci_conn_complete_evt(struct hci_dev *hdev, void *data,
>>>               }
>>>       }
>>>
>>> +     /* The HCI_Connection_Complete event is only sent once per connection.
>>> +      * Processing it more than once per connection can corrupt kernel memory.
>>> +      *
>>> +      * As the connection handle is set here for the first time, it indicates
>>> +      * whether the connection is already set up.
>>> +      */
>>> +     if (conn->handle) {
>>> +             bt_dev_err(hdev, "Ignoring HCI_Connection_Complete for existing connection");
>>> +             goto unlock;
>>> +     }
>>> +
>>>       if (!ev->status) {
>>>               conn->handle = __le16_to_cpu(ev->handle);
>>>
> 
> 
> 

Best
Sönke