FAILED: patch "[PATCH] Bluetooth: hci_core: use skb_get() instead of skb_clone() for" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x f5afdff569a09d1cb8cf19826199d024725576cb
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090331-cheddar-preheated-6153@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f5afdff569a09d1cb8cf19826199d024725576cb Mon Sep 17 00:00:00 2001
From: Xin Chen <[email protected]>
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/[email protected]/

index 509c820a693d..35a1be57e386 100644
@@ -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;