[PATCH] Bluetooth: Avoid potential use-after-free in hci_error_reset

[Ying Hsu <yinghsu@xxxxxxxxxxxx>]

While handling the HCI_EV_HARDWARE_ERROR event, if the underlying
BT controller is not responding, the GPIO reset mechanism would
free the hci_dev and lead to a use-after-free in hci_error_reset.

Here's the call trace observed on a ChromeOS device with Intel AX201:
   queue_work_on+0x3e/0x6c
   __hci_cmd_sync_sk+0x2ee/0x4c0 [bluetooth <HASH:3b4a6>]
   ? init_wait_entry+0x31/0x31
   __hci_cmd_sync+0x16/0x20 [bluetooth <HASH:3b4a 6>]
   hci_error_reset+0x4f/0xa4 [bluetooth <HASH:3b4a 6>]
   process_one_work+0x1d8/0x33f
   worker_thread+0x21b/0x373
   kthread+0x13a/0x152
   ? pr_cont_work+0x54/0x54
   ? kthread_blkcg+0x31/0x31
    ret_from_fork+0x1f/0x30

This patch holds the reference count on the hci_dev while processing
a HCI_EV_HARDWARE_ERROR event to avoid potential crash.

Signed-off-by: Ying Hsu <yinghsu@xxxxxxxxxxxx>
---
Tested this commit on a chromebook with Intel BT controller.

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

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 65601aa52e0d..a42417926028 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -1049,6 +1049,7 @@ static void hci_error_reset(struct work_struct *work)
 {
 	struct hci_dev *hdev = container_of(work, struct hci_dev, error_reset);
 
+	hci_dev_hold(hdev);
 	BT_DBG("%s", hdev->name);
 
 	if (hdev->hw_error)
@@ -1060,6 +1061,7 @@ static void hci_error_reset(struct work_struct *work)
 		return;
 
 	hci_dev_do_open(hdev);
+	hci_dev_put(hdev);
 }
 
 void hci_uuids_clear(struct hci_dev *hdev)
-- 
2.43.0.472.g3155946c3a-goog