From f5afdff569a09d1cb8cf19826199d024725576cb Mon Sep 17 00:00:00 2001 From: Xin Chen Date: Wed, 19 Aug 2026 21:53:21 +0800 Subject: [PATCH] Bluetooth: hci_core: use skb_get() instead of skb_clone() for req_skb BT enable fails intermittently with -ETIMEDOUT (-110). The kernel log shows the HCI Read Local Version command was sent and the firmware replied with status 0x00 (logged by hci_req_cmd_complete() BT_DBG), but the waiter in __hci_cmd_sync_sk() never woke up and timed out after 10 s: bluetooth hci0: Opcode 0xfc00 // __hci_cmd_sync_sk bluetooth hci0: opcode 0xfc00 plen 1 // hci_cmd_sync_add bluetooth hci0: skb len 4 // hci_cmd_sync_alloc bluetooth hci0: length 1 // hci_req_sync_run Bluetooth: hci0 cmd_cnt 1 cmd queued 1 // hci_cmd_work Bluetooth: hci0 type 1 len 4 // hci_send_frame Bluetooth: opcode 0xfc00 status 0x00 // hci_req_cmd_complete <-- req_skb NULL: req_complete_skb not set, hci_cmd_sync_complete() never called, req_status stays HCI_REQ_PEND --> <-- 10 s later: wait_event_interruptible_timeout expires --> bluetooth hci0: end: err -110 // __hci_cmd_sync_sk The root cause is that hci_send_cmd_sync() clones the sent command into hdev->req_skb so that hci_req_cmd_complete() can locate the registered completion callback. Under memory pressure this skb_clone() fails, leaving hdev->req_skb NULL. The firmware reply is received and processed, but hci_req_cmd_complete() finds NULL req_skb, so hci_cmd_sync_complete() is never called, req_status stays HCI_REQ_PEND, and the waiter times out with -ETIMEDOUT. req_skb is only used to read bt_cb(skb)->hci callbacks and opcode -- it is never modified. Replace skb_clone() with skb_get(), which simply increments the reference count of hdev->sent_cmd without allocating new memory and therefore cannot fail. This issue was first observed as a use-after-free in ttyport_close() when ttyport_open() failed, which was investigated in an earlier patch series [1]. That investigation led to the discovery of the true root cause described above. [1] https://lore.kernel.org/all/20250430111617.1151390-1-quic_cxin@quicinc.com/ Fixes: 2615fd9a7c25 ("Bluetooth: hci_sync: Fix overwriting request callback") Cc: stable@vger.kernel.org Signed-off-by: Xin Chen Signed-off-by: Luiz Augusto von Dentz --- net/bluetooth/hci_core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c index 509c820a693d..35a1be57e386 100644 --- a/net/bluetooth/hci_core.c +++ b/net/bluetooth/hci_core.c @@ -4093,7 +4093,7 @@ static int hci_send_cmd_sync(struct hci_dev *hdev, struct sk_buff *skb) if (READ_ONCE(hdev->req_status) == HCI_REQ_PEND && !hci_dev_test_and_set_flag(hdev, HCI_CMD_PENDING)) { kfree_skb(hdev->req_skb); - hdev->req_skb = skb_clone(hdev->sent_cmd, GFP_KERNEL); + hdev->req_skb = skb_get(hdev->sent_cmd); } return err;