Re: [PATCH v2] Bluetooth: Fix tracking local SSP authentication requirement

[Szymon Janc <szymon.janc@tieto.com>]

Hi,

On Friday 11 of July 2014 15:32:23 johan.hedberg@gmail.com wrote:
> From: Johan Hedberg <johan.hedberg@intel.com>
> 
> When we need to make the decision whether to perform just-works or real
> user confirmation we need to know the exact local authentication
> requirement that was passed to the controller. So far conn->auth_type
> (the local requirement) wasn't in one case updated appropriately in fear
> of the user confirmation being rejected later.
> 
> The real problem however was not really that conn->auth_type couldn't
> represent the true value but that we were checking the local MITM
> requirement in an incorrect way. It's perfectly fine to let auth_type
> follow what we tell the controller since we're still tracking the target
> security level with conn->pending_sec_level.
> 
> This patch updates the check for local MITM requirement in the
> hci_user_confirm_request_evt function to use the locally requested
> security level and ensures that auth_type always represents what we tell
> the controller. All other code in hci_user_confirm_request_evt still
> uses the auth_type instead of pending_sec_level for determining whether
> to do just-works or not, since that's the only value that's in sync with
> what the remote device knows.
> 
> Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
> ---
>  net/bluetooth/hci_event.c | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index f0f220057f21..8980bd24b8c0 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -3664,18 +3664,14 @@ static void hci_io_capa_request_evt(struct hci_dev *hdev, struct sk_buff *skb)
>  
>  		/* If we are initiators, there is no remote information yet */
>  		if (conn->remote_auth == 0xff) {
> -			cp.authentication = conn->auth_type;
> -
>  			/* Request MITM protection if our IO caps allow it
>  			 * except for the no-bonding case.
> -			 * conn->auth_type is not updated here since
> -			 * that might cause the user confirmation to be
> -			 * rejected in case the remote doesn't have the
> -			 * IO capabilities for MITM.
>  			 */
>  			if (conn->io_capability != HCI_IO_NO_INPUT_OUTPUT &&
>  			    cp.authentication != HCI_AT_NO_BONDING)
> -				cp.authentication |= 0x01;
> +				conn->auth_type |= 0x01;
> +
> +			cp.authentication = conn->auth_type;
>  		} else {
>  			conn->auth_type = hci_get_auth_req(conn);
>  			cp.authentication = conn->auth_type;
> @@ -3747,9 +3743,12 @@ static void hci_user_confirm_request_evt(struct hci_dev *hdev,
>  	rem_mitm = (conn->remote_auth & 0x01);
>  
>  	/* If we require MITM but the remote device can't provide that
> -	 * (it has NoInputNoOutput) then reject the confirmation request
> +	 * (it has NoInputNoOutput) then reject the confirmation
> +	 * request. We check the security level here since it doesn't
> +	 * necessarily match conn->auth_type.
>  	 */
> -	if (loc_mitm && conn->remote_cap == HCI_IO_NO_INPUT_OUTPUT) {
> +	if (conn->pending_sec_level > BT_SECURITY_MEDIUM &&
> +	    conn->remote_cap == HCI_IO_NO_INPUT_OUTPUT) {
>  		BT_DBG("Rejecting request: remote device can't provide MITM");
>  		hci_send_cmd(hdev, HCI_OP_USER_CONFIRM_NEG_REPLY,
>  			     sizeof(ev->bdaddr), &ev->bdaddr);
> 

I've tested this on Android with CTS secure/insecure server scenarios and this
seems to work OK. Also tested pairing with Nokia BH-505 headset.

Tested-by: Szymon Janc <szymon.janc@tieto.com>

-- 
Best regards, 
Szymon Janc