Received-SPF: pass (google.com: domain of linux-bluetooth-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] Bluetooth: skip invalid hci_sync_conn_complete_evt
To:     Marcel Holtmann <marcel@holtmann.org>
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>,
        skhan@linuxfoundation.org, gregkh@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        syzbot+66264bf2fd0476be7e6c@syzkaller.appspotmail.com
References: <20210721101710.82974-1-desmondcheongzx@gmail.com>
 <A47B24AE-C807-4ADA-B0F7-8283ACC83BF7@holtmann.org>
From:   Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Message-ID: <30d1e002-4739-4ce4-2857-77404e4dfb68@gmail.com>
Date:   Wed, 28 Jul 2021 14:47:18 +0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.11.0
MIME-Version: 1.0
In-Reply-To: <A47B24AE-C807-4ADA-B0F7-8283ACC83BF7@holtmann.org>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 22/7/21 10:39 pm, Marcel Holtmann wrote:
> 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@syzkaller.appspotmail.com
>> Tested-by: syzbot+66264bf2fd0476be7e6c@syzkaller.appspotmail.com
>> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.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.
> 

Hi Marcel,

Apologies for the delayed response.

Thanks for the feedback, I'll add more elaboration for the new check and 
add a bt_dev_err in a v2 patch.

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