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

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Date:   Mon,  8 Nov 2021 20:01:06 +0000
From:   Jesse Melhuish <melhuishj@...omium.org>
To:     linux-bluetooth@...r.kernel.org
Cc:     Jesse Melhuish <melhuishj@...omium.org>,
        Abhishek Pandit-Subedi <abhishekpandit@...omium.org>,
        Sonny Sasaka <sonnysasaka@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH v2] Bluetooth: Don't initialize msft/aosp when using user channel

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]
> HCI Event: Command Complete (0x0e) plen 5                   #5 [hci0]
      Vendor (0x3f|0x001e) ncmd 1
	Status: Command Disallowed (0x0c)
	05                                               .
> HCI Event: Command Complete (0x0e) plen 4                   #6 [hci0]
      Reset (0x03|0x0003) ncmd 2
	Status: Success (0x00)

Signed-off-by: Jesse Melhuish <melhuishj@...omium.org>
Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
Reviewed-by: Sonny Sasaka <sonnysasaka@...omium.org>
---

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);
+	}
 
 	clear_bit(HCI_INIT, &hdev->flags);
 
-- 
2.31.0