linux-kernel - [PATCH v2] Bluetooth: hci_core: fix init for HCI_USER

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Message-Id: <20191017032039.18413-1-mkorpershoek@baylibre.com>
Date:   Wed, 16 Oct 2019 20:20:39 -0700
From:   Mattijs Korpershoek <mkorpershoek@...libre.com>
To:     linux-bluetooth@...r.kernel.org
Cc:     Mattijs Korpershoek <mkorpershoek@...libre.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] Bluetooth: hci_core: fix init for HCI_USER_CHANNEL

During the setup() stage, HCI device drivers expect the chip to
acknowledge its setup() completion via vendor specific frames.

If userspace opens() such HCI device in HCI_USER_CHANNEL [1] mode,
the vendor specific frames are never tranmitted to the driver, as
they are filtered in hci_rx_work().

Allow HCI devices which operate in HCI_USER_CHANNEL mode to receive
frames if the HCI device is is HCI_INIT state.

[1] https://www.spinics.net/lists/linux-bluetooth/msg37345.html

Fixes: 23500189d7e0 ("Bluetooth: Introduce new HCI socket channel for user operation")
Signed-off-by: Mattijs Korpershoek <mkorpershoek@...libre.com>
---
Changelog:
v2:
* change test logic to transfer packets when in INIT phase
  for user channel mode as recommended by Marcel
* renamed patch from
  "Bluetooth: hci_core: fix init with HCI_QUIRK_NON_PERSISTENT_SETUP"

v1:
 * https://lkml.org/lkml/2019/10/3/2250

Some more background on the change follows:

The Android bluetooth stack (Bluedroid) also has a HAL implementation
which follows Linux's standard rfkill interface [1].

This implementation relies on the HCI_CHANNEL_USER feature to get
exclusive access to the underlying bluetooth device.

When testing this along with the btkmtksdio driver, the
chip appeared unresponsive when calling the following from userspace:

    struct sockaddr_hci addr;
    int fd;

    fd = socket(AF_BLUETOOTH, SOCK_RAW, BTPROTO_HCI);

    memset(&addr, 0, sizeof(addr));
    addr.hci_family = AF_BLUETOOTH;
    addr.hci_dev = 0;
    addr.hci_channel = HCI_CHANNEL_USER;

    bind(fd, (struct sockaddr *) &addr, sizeof(addr)); # device hangs

In the case of bluetooth drivers exposing QUIRK_NON_PERSISTENT_SETUP
such as btmtksdio, setup() is called each multiple times.
In particular, when userspace calls bind(), the setup() is called again
and vendor specific commands might be send to re-initialize the chip.

Those commands are filtered out by hci_core in HCI_CHANNEL_USER mode,
preventing setup() from completing successfully.

This has been tested on a 4.19 kernel based on Android Common Kernel.
It has also been compile tested on bluetooth-next.

[1] https://android.googlesource.com/platform/system/bt/+/refs/heads/master/vendor_libs/linux/interface/

 net/bluetooth/hci_core.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index b2559d4bed81..0cc9ce917222 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -4440,7 +4440,14 @@ static void hci_rx_work(struct work_struct *work)
 			hci_send_to_sock(hdev, skb);
 		}

-		if (hci_dev_test_flag(hdev, HCI_USER_CHANNEL)) {
+		/* If the device has been opened in HCI_USER_CHANNEL,
+		 * the userspace has exclusive access to device.
+		 * When device is HCI_INIT, we still need to process
+		 * the data packets to the driver in order
+		 * to complete its setup().
+		 */
+		if (hci_dev_test_flag(hdev, HCI_USER_CHANNEL) &&
+		    !test_bit(HCI_INIT, &hdev->flags)) {
 			kfree_skb(skb);
 			continue;
 		}
-- 
2.20.1