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Message-Id: <3860C10A-DA02-49F0-9EDF-13BFF3C6C197@holtmann.org>
Date: Mon, 29 Jun 2020 22:20:59 +0200
From: Marcel Holtmann <marcel@...tmann.org>
To: Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc: Archie Pusaka <apusaka@...gle.com>,
linux-bluetooth <linux-bluetooth@...r.kernel.org>,
chromeos-bluetooth-upstreaming
<chromeos-bluetooth-upstreaming@...omium.org>,
Archie Pusaka <apusaka@...omium.org>,
Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Johan Hedberg <johan.hedberg@...il.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH v1 2/2] Bluetooth: queue L2CAP conn req if encryption
is needed
Hi Luiz,
>>> It is possible to receive an L2CAP conn req for an encrypted
>>> connection, before actually receiving the HCI change encryption
>>> event. If this happened, the received L2CAP packet will be ignored.
>
> How is this possible? Or you are referring to a race between the ACL
> and Event endpoint where the Encryption Change is actually pending to
> be processed but we end up processing the ACL data first.
you get the ACL packet with the L2CAP_Connect_Req in it and then the HCI Encryption Change event. However over the air they go in the different order. It is specific to the USB transport and nothing is going to fix this. The USB transport design is borked. You can only do bandaids.
>>> This patch queues the L2CAP packet and process them after the
>>> expected HCI event is received. If after 2 seconds we still don't
>>> receive it, then we assume something bad happened and discard the
>>> queued packets.
>>
>> as with the other patch, this should be behind the same quirk and experimental setting for exactly the same reasons.
>>
>>>
>>> Signed-off-by: Archie Pusaka <apusaka@...omium.org>
>>> Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
>>>
>>> ---
>>>
>>> include/net/bluetooth/bluetooth.h | 6 +++
>>> include/net/bluetooth/l2cap.h | 6 +++
>>> net/bluetooth/hci_event.c | 3 ++
>>> net/bluetooth/l2cap_core.c | 87 +++++++++++++++++++++++++++----
>>> 4 files changed, 91 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/include/net/bluetooth/bluetooth.h b/include/net/bluetooth/bluetooth.h
>>> index 7ee8041af803..e64278401084 100644
>>> --- a/include/net/bluetooth/bluetooth.h
>>> +++ b/include/net/bluetooth/bluetooth.h
>>> @@ -335,7 +335,11 @@ struct l2cap_ctrl {
>>> u16 reqseq;
>>> u16 txseq;
>>> u8 retries;
>>> + u8 rsp_code;
>>> + u8 amp_id;
>>> + __u8 ident;
>>> __le16 psm;
>>> + __le16 scid;
>>> bdaddr_t bdaddr;
>>> struct l2cap_chan *chan;
>>> };
>>
>> I would not bother trying to make this work with CREATE_CHAN_REQ. That is if you want to setup a L2CAP channel that can be moved between BR/EDR and AMP controllers and in that case you have to read the L2CAP information and features first. Meaning there will have been unencrypted ACL packets. This problem only exists if the remote side doesn’t request any version information first.
>>
>>> @@ -374,6 +378,8 @@ struct bt_skb_cb {
>>> struct hci_ctrl hci;
>>> };
>>> };
>>> +static_assert(sizeof(struct bt_skb_cb) <= sizeof(((struct sk_buff *)0)->cb));
>>> +
>>> #define bt_cb(skb) ((struct bt_skb_cb *)((skb)->cb))
>>>
>>> #define hci_skb_pkt_type(skb) bt_cb((skb))->pkt_type
>>> diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
>>> index 8f1e6a7a2df8..f8f6dec96f12 100644
>>> --- a/include/net/bluetooth/l2cap.h
>>> +++ b/include/net/bluetooth/l2cap.h
>>> @@ -58,6 +58,7 @@
>>> #define L2CAP_MOVE_ERTX_TIMEOUT msecs_to_jiffies(60000)
>>> #define L2CAP_WAIT_ACK_POLL_PERIOD msecs_to_jiffies(200)
>>> #define L2CAP_WAIT_ACK_TIMEOUT msecs_to_jiffies(10000)
>>> +#define L2CAP_PEND_ENC_CONN_TIMEOUT msecs_to_jiffies(2000)
>>>
>>> #define L2CAP_A2MP_DEFAULT_MTU 670
>>>
>>> @@ -700,6 +701,9 @@ struct l2cap_conn {
>>> struct mutex chan_lock;
>>> struct kref ref;
>>> struct list_head users;
>>> +
>>> + struct delayed_work remove_pending_encrypt_conn;
>>> + struct sk_buff_head pending_conn_q;
>>> };
>>>
>>> struct l2cap_user {
>>> @@ -1001,4 +1005,6 @@ void l2cap_conn_put(struct l2cap_conn *conn);
>>> int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user);
>>> void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user);
>>>
>>> +void l2cap_process_pending_encrypt_conn(struct hci_conn *hcon);
>>> +
>>> #endif /* __L2CAP_H */
>>> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
>>> index 108c6c102a6a..8cefc51a5ca4 100644
>>> --- a/net/bluetooth/hci_event.c
>>> +++ b/net/bluetooth/hci_event.c
>>> @@ -3136,6 +3136,9 @@ static void hci_encrypt_change_evt(struct hci_dev *hdev, struct sk_buff *skb)
>>>
>>> unlock:
>>> hci_dev_unlock(hdev);
>>> +
>>> + if (conn && !ev->status && ev->encrypt)
>>> + l2cap_process_pending_encrypt_conn(conn);
>>> }
>>>
>>> static void hci_change_link_key_complete_evt(struct hci_dev *hdev,
>>> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
>>> index 35d2bc569a2d..fc6fe2c80c46 100644
>>> --- a/net/bluetooth/l2cap_core.c
>>> +++ b/net/bluetooth/l2cap_core.c
>>> @@ -62,6 +62,10 @@ static void l2cap_send_disconn_req(struct l2cap_chan *chan, int err);
>>> static void l2cap_tx(struct l2cap_chan *chan, struct l2cap_ctrl *control,
>>> struct sk_buff_head *skbs, u8 event);
>>>
>>> +static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
>>> + u8 ident, u8 *data, u8 rsp_code,
>>> + u8 amp_id, bool queue_if_fail);
>>> +
>>> static inline u8 bdaddr_type(u8 link_type, u8 bdaddr_type)
>>> {
>>> if (link_type == LE_LINK) {
>>> @@ -1902,6 +1906,8 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
>>> if (conn->info_state & L2CAP_INFO_FEAT_MASK_REQ_SENT)
>>> cancel_delayed_work_sync(&conn->info_timer);
>>>
>>> + cancel_delayed_work_sync(&conn->remove_pending_encrypt_conn);
>>> +
>>> hcon->l2cap_data = NULL;
>>> conn->hchan = NULL;
>>> l2cap_conn_put(conn);
>>> @@ -2023,6 +2029,55 @@ static void l2cap_retrans_timeout(struct work_struct *work)
>>> l2cap_chan_put(chan);
>>> }
>>>
>>> +static void l2cap_add_pending_encrypt_conn(struct l2cap_conn *conn,
>>> + struct l2cap_conn_req *req,
>>> + u8 ident, u8 rsp_code, u8 amp_id)
>>> +{
>>> + struct sk_buff *skb = bt_skb_alloc(0, GFP_KERNEL);
>>> +
>>> + bt_cb(skb)->l2cap.psm = req->psm;
>>> + bt_cb(skb)->l2cap.scid = req->scid;
>>> + bt_cb(skb)->l2cap.ident = ident;
>>> + bt_cb(skb)->l2cap.rsp_code = rsp_code;
>>> + bt_cb(skb)->l2cap.amp_id = amp_id;
>>> +
>>> + skb_queue_tail(&conn->pending_conn_q, skb);
>>> + queue_delayed_work(conn->hcon->hdev->workqueue,
>>> + &conn->remove_pending_encrypt_conn,
>>> + L2CAP_PEND_ENC_CONN_TIMEOUT);
>>> +}
>>> +
>>> +void l2cap_process_pending_encrypt_conn(struct hci_conn *hcon)
>>> +{
>>> + struct sk_buff *skb;
>>> + struct l2cap_conn *conn = hcon->l2cap_data;
>>> +
>>> + if (!conn)
>>> + return;
>>> +
>>> + while ((skb = skb_dequeue(&conn->pending_conn_q))) {
>>> + struct l2cap_conn_req req;
>>> + u8 ident, rsp_code, amp_id;
>>> +
>>> + req.psm = bt_cb(skb)->l2cap.psm;
>>> + req.scid = bt_cb(skb)->l2cap.scid;
>>> + ident = bt_cb(skb)->l2cap.ident;
>>> + rsp_code = bt_cb(skb)->l2cap.rsp_code;
>>> + amp_id = bt_cb(skb)->l2cap.amp_id;
>>> +
>>> + l2cap_connect(conn, ident, (u8 *)&req, rsp_code, amp_id, false);
>>> + kfree_skb(skb);
>>> + }
>>> +}
>>> +
>>> +static void l2cap_remove_pending_encrypt_conn(struct work_struct *work)
>>> +{
>>> + struct l2cap_conn *conn = container_of(work, struct l2cap_conn,
>>> + remove_pending_encrypt_conn.work);
>>> +
>>> + l2cap_process_pending_encrypt_conn(conn->hcon);
>>> +}
>>> +
>>> static void l2cap_streaming_send(struct l2cap_chan *chan,
>>> struct sk_buff_head *skbs)
>>> {
>>> @@ -4076,8 +4131,8 @@ static inline int l2cap_command_rej(struct l2cap_conn *conn,
>>> }
>>>
>>> static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
>>> - struct l2cap_cmd_hdr *cmd,
>>> - u8 *data, u8 rsp_code, u8 amp_id)
>>> + u8 ident, u8 *data, u8 rsp_code,
>>> + u8 amp_id, bool queue_if_fail)
>>> {
>>> struct l2cap_conn_req *req = (struct l2cap_conn_req *) data;
>>> struct l2cap_conn_rsp rsp;
>>> @@ -4103,8 +4158,15 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn,
>>> /* Check if the ACL is secure enough (if not SDP) */
>>> if (psm != cpu_to_le16(L2CAP_PSM_SDP) &&
>>> !hci_conn_check_link_mode(conn->hcon)) {
>>> - conn->disc_reason = HCI_ERROR_AUTH_FAILURE;
>>> - result = L2CAP_CR_SEC_BLOCK;
>>> + if (!queue_if_fail) {
>>> + conn->disc_reason = HCI_ERROR_AUTH_FAILURE;
>>> + result = L2CAP_CR_SEC_BLOCK;
>>> + goto response;
>>> + }
>>> +
>>> + l2cap_add_pending_encrypt_conn(conn, req, ident, rsp_code,
>>> + amp_id);
>>> + result = L2CAP_CR_PEND;
>>> goto response;
>>> }
>>
>> So I am actually wondering if the approach is not better to send back a pending to the connect request like we do for everything else. And then proceed with getting our remote L2CAP information. If these come back in encrypted, then we can assume that we actually had encryption enabled and proceed with a L2CAP connect response saying that all is fine.
>
> I wonder if we should resolve this by having different queues in
> hci_recv_frame (e.g. hdev->evt_rx), that way we can dequeue the HCI
> events before ACL so we first update the HCI states before start
> processing the L2CAP data, thoughts? Something like this:
>
> https://gist.github.com/Vudentz/464fb0065a73e5c99bdb66cd2c5a1a2d
No. We need to keep things serialized. We actually have to reject unencrypted packets.
So whatever we do needs to be behind a quirk and an explicit opt-in.
Regards
Marcel
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