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

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Message-Id: <17BDA821-9D4A-46C9-8C0E-F7DB35D50033@holtmann.org>
Date:   Thu, 11 Nov 2021 19:43:14 +0100
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Jesse Melhuish <melhuishj@...omium.org>
Cc:     linux-bluetooth <linux-bluetooth@...r.kernel.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>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2] Bluetooth: Don't initialize msft/aosp when using user
 channel

Hi Jesse,

> 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);
> +	}

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