netdev - [PATCH] Bluetooth: Always call advertising disable before setting params

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Date:   Tue, 23 Mar 2021 14:18:21 -0700
From:   Daniel Winkler <danielwinkler@...gle.com>
To:     linux-bluetooth@...r.kernel.org
Cc:     chromeos-bluetooth-upstreaming@...omium.org,
        Daniel Winkler <danielwinkler@...gle.com>,
        Miao-chen Chou <mcchou@...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: Always call advertising disable before setting params

In __hci_req_enable_advertising, the HCI_LE_ADV hdev flag is temporarily
cleared to allow the random address to be set, which exposes a race
condition when an advertisement is configured immediately (<10ms) after
software rotation starts to refresh an advertisement.

In normal operation, the HCI_LE_ADV flag is updated as follows:

1. adv_timeout_expire is called, HCI_LE_ADV gets cleared in
   __hci_req_enable_advertising, but hci_req configures an enable
   request
2. hci_req is run, enable callback re-sets HCI_LE_ADV flag

However, in this race condition, the following occurs:

1. adv_timeout_expire is called, HCI_LE_ADV gets cleared in
   __hci_req_enable_advertising, but hci_req configures an enable
   request
2. add_advertising is called, which also calls
   __hci_req_enable_advertising. Because HCI_LE_ADV was cleared in Step
   1, no "disable" command is queued.
3. hci_req for adv_timeout_expire is run, which enables advertising and
   re-sets HCI_LE_ADV
4. hci_req for add_advertising is run, but because no "disable" command
   was queued, we try to set advertising parameters while advertising is
   active, causing a Command Disallowed error, failing the registration.

To resolve the issue, this patch removes the check for the HCI_LE_ADV
flag, and always queues the "disable" request, since HCI_LE_ADV could be
very temporarily out-of-sync. According to the spec, there is no harm in
calling "disable" when advertising is not active.

Reviewed-by: Miao-chen Chou <mcchou@...omium.org>
Signed-off-by: Daniel Winkler <danielwinkler@...gle.com>
---

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

diff --git a/net/bluetooth/hci_request.c b/net/bluetooth/hci_request.c
index 8ace5d34b01efe..2b4b99f4cedf21 100644
--- a/net/bluetooth/hci_request.c
+++ b/net/bluetooth/hci_request.c
@@ -1547,8 +1547,10 @@ void __hci_req_enable_advertising(struct hci_request *req)
 	if (!is_advertising_allowed(hdev, connectable))
 		return;

-	if (hci_dev_test_flag(hdev, HCI_LE_ADV))
-		__hci_req_disable_advertising(req);
+	/* Request that the controller stop advertising. This can be called
+	 * whether or not there is an active advertisement.
+	 */
+	__hci_req_disable_advertising(req);

 	/* Clear the HCI_LE_ADV bit temporarily so that the
 	 * hci_update_random_address knows that it's safe to go ahead
-- 
2.31.0.291.g576ba9dcdaf-goog