Re: [PATCH v2] Bluetooth: Don't initialize msft/aosp when using user channel

Hi Marcel,

No problem, thanks. Happy to extend userchan-tester; do you mind if we
continue reviewing this patch for approval in the meantime so we can
mitigate the issue on our end?

On Thu, Nov 11, 2021 at 12:43 PM Marcel Holtmann [off-list ref] wrote:

Hi Jesse,

quoted

A race condition is triggered when usermode control is given to
userspace before the kernel's MSFT query responds, resulting in an
unexpected response to userspace's reset command.

Issue can be observed in btmon:
< HCI Command: Vendor (0x3f|0x001e) plen 2                    #3 [hci0]
       05 01                                            ..
@ USER Open: bt_stack_manage (privileged) version 2.22  {0x0002} [hci0]
< HCI Command: Reset (0x03|0x0003) plen 0                     #4 [hci0]

quoted

HCI Event: Command Complete (0x0e) plen 5                   #5 [hci0]

     Vendor (0x3f|0x001e) ncmd 1
      Status: Command Disallowed (0x0c)
      05                                               .

quoted

HCI Event: Command Complete (0x0e) plen 4                   #6 [hci0]

     Reset (0x03|0x0003) ncmd 2
      Status: Success (0x00)

Signed-off-by: Jesse Melhuish <redacted>
Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Reviewed-by: Sonny Sasaka <redacted>
---

Changes in v2:
- Moved guard to the new home for this code.

net/bluetooth/hci_sync.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index b794605dc882..5f1f59ac1813 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c

@@ -3887,8 +3887,10 @@ int hci_dev_open_sync(struct hci_dev *hdev)
          hci_dev_test_flag(hdev, HCI_VENDOR_DIAG) && hdev->set_diag)
              ret = hdev->set_diag(hdev, true);

-     msft_do_open(hdev);
-     aosp_do_open(hdev);
+     if (!hci_dev_test_flag(hdev, HCI_USER_CHANNEL)) {
+             msft_do_open(hdev);
+             aosp_do_open(hdev);
+     }

but then you need to do the same on hci_dev_close. Also it would be good to extend userchan-tester with test cases for this.

Regards

Marcel