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

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Message-Id: <20211105222820.1.I2a8b2f2e52d05ae9ead3f3dcc1dd90ef47a7acd7@changeid>
Date:   Fri,  5 Nov 2021 22:28:37 +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] 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)

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

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

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index c07b2d2a44b0..2b5df597e7ed 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -1595,8 +1595,10 @@ static int hci_dev_do_open(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