Bluetooth: hci_sync: Push sync command cancellation to workqueue

syzbot reported that hci_cmd_sync_cancel may sleep from the wrong
context. To avoid this, create a new work item that pushes the relevant
parts into a different context.

Note that we keep the old implementation with the name
__hci_cmd_sync_cancel as the sleeping behaviour is desired in some
cases.

Reported-and-tested-by: syzbot+485cc00ea7cf41dfdbf1@syzkaller.appspotmail.com
Fixes: c97a747e ("Bluetooth: btusb: Cancel sync commands for certain URB errors")
Signed-off-by: Benjamin Berg <bberg@redhat.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/hci_core.h

@@ -480,6 +480,7 @@ struct hci_dev {
 	struct work_struct	cmd_sync_work;
 	struct list_head	cmd_sync_work_list;
 	struct mutex		cmd_sync_work_lock;
+	struct work_struct	cmd_sync_cancel_work;
 
 	__u16			discov_timeout;
 	struct delayed_work	discov_off;

include/net/bluetooth/hci_sync.h

@@ -38,6 +38,7 @@ int __hci_cmd_sync_status_sk(struct hci_dev *hdev, u16 opcode, u32 plen,
 void hci_cmd_sync_init(struct hci_dev *hdev);
 void hci_cmd_sync_clear(struct hci_dev *hdev);
 void hci_cmd_sync_cancel(struct hci_dev *hdev, int err);
+void __hci_cmd_sync_cancel(struct hci_dev *hdev, int err);
 
 int hci_cmd_sync_queue(struct hci_dev *hdev, hci_cmd_sync_work_func_t func,
 		       void *data, hci_cmd_sync_work_destroy_t destroy);

net/bluetooth/hci_core.c

@@ -3859,7 +3859,7 @@ static void hci_cmd_work(struct work_struct *work)
 
 			res = hci_send_frame(hdev, skb);
 			if (res < 0)
-				hci_cmd_sync_cancel(hdev, -res);
+				__hci_cmd_sync_cancel(hdev, -res);
 
 			if (test_bit(HCI_RESET, &hdev->flags))
 				cancel_delayed_work(&hdev->cmd_timer);

net/bluetooth/hci_request.c

@@ -2692,7 +2692,7 @@ void hci_request_setup(struct hci_dev *hdev)
 
 void hci_request_cancel_all(struct hci_dev *hdev)
 {
-	hci_cmd_sync_cancel(hdev, ENODEV);
+	__hci_cmd_sync_cancel(hdev, ENODEV);
 
 	cancel_work_sync(&hdev->discov_update);
 	cancel_work_sync(&hdev->scan_update);

net/bluetooth/hci_sync.c

@@ -313,11 +313,24 @@ static void hci_cmd_sync_work(struct work_struct *work)
 	}
 }
 
+static void hci_cmd_sync_cancel_work(struct work_struct *work)
+{
+	struct hci_dev *hdev = container_of(work, struct hci_dev, cmd_sync_cancel_work);
+
+	cancel_delayed_work_sync(&hdev->cmd_timer);
+	cancel_delayed_work_sync(&hdev->ncmd_timer);
+	atomic_set(&hdev->cmd_cnt, 1);
+
+	wake_up_interruptible(&hdev->req_wait_q);
+}
+
 void hci_cmd_sync_init(struct hci_dev *hdev)
 {
 	INIT_WORK(&hdev->cmd_sync_work, hci_cmd_sync_work);
 	INIT_LIST_HEAD(&hdev->cmd_sync_work_list);
 	mutex_init(&hdev->cmd_sync_work_lock);
+
+	INIT_WORK(&hdev->cmd_sync_cancel_work, hci_cmd_sync_cancel_work);
 }
 
 void hci_cmd_sync_clear(struct hci_dev *hdev)
@@ -335,7 +348,7 @@ void hci_cmd_sync_clear(struct hci_dev *hdev)
 	}
 }
 
-void hci_cmd_sync_cancel(struct hci_dev *hdev, int err)
+void __hci_cmd_sync_cancel(struct hci_dev *hdev, int err)
 {
 	bt_dev_dbg(hdev, "err 0x%2.2x", err);
 
@@ -350,6 +363,18 @@ void hci_cmd_sync_cancel(struct hci_dev *hdev, int err)
 		wake_up_interruptible(&hdev->req_wait_q);
 	}
 }
+
+void hci_cmd_sync_cancel(struct hci_dev *hdev, int err)
+{
+	bt_dev_dbg(hdev, "err 0x%2.2x", err);
+
+	if (hdev->req_status == HCI_REQ_PEND) {
+		hdev->req_result = err;
+		hdev->req_status = HCI_REQ_CANCELED;
+
+		queue_work(hdev->workqueue, &hdev->cmd_sync_cancel_work);
+	}
+}
 EXPORT_SYMBOL(hci_cmd_sync_cancel);
 
 int hci_cmd_sync_queue(struct hci_dev *hdev, hci_cmd_sync_work_func_t func,