linux-kernel - Re: [PATCH] Bluetooth: fix use-after-free in hci_conn

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Message-ID: <20260209132535.2716-1-hdanton@sina.com>
Date: Mon,  9 Feb 2026 21:25:33 +0800
From: Hillf Danton <hdanton@...a.com>
To: Masahiro Kawada <youjingxiaogao2@...il.com>
Cc: linux-bluetooth@...r.kernel.org,
	luiz.dentz@...il.com,
	marcel@...tmann.org,
	johan.hedberg@...il.com,
	linux-kernel@...r.kernel.org,
	syzbot+3609b9b48e68e1fe47fd@...kaller.appspotmail.com
Subject: Re: [PATCH] Bluetooth: fix use-after-free in hci_conn_drop

On Mon,  9 Feb 2026 19:02:11 +0900 Masahiro Kawada wrote:
> Fix a use-after-free in hci_conn_drop triggered via hci_cmd_sync_work.
> 
> In hci_conn_del(), hci_cmd_sync_dequeue() is called after
> hci_conn_cleanup() which may have already freed the conn pointer.
> Fix by moving the dequeue before cleanup.
> 
> Additionally, le_read_features_complete() calls hci_conn_drop(conn)
> without checking whether conn is still valid. When
> hci_le_read_remote_features_sync() blocks waiting for an HCI event,
> another thread can free conn through hci_conn_del(). Fix by adding
> a hci_conn_valid() check before calling hci_conn_drop().
> 
> Fixes: 881559af5f5c ("Bluetooth: hci_sync: Attempt to dequeue connection attempt")
> Fixes: a106e50be74b ("Bluetooth: HCI: Add support for LL Extended Feature Set")
> Reported-by: syzbot+3609b9b48e68e1fe47fd@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=3609b9b48e68e1fe47fd
> Tested-by: syzbot+3609b9b48e68e1fe47fd@...kaller.appspotmail.com
> Signed-off-by: Masahiro Kawada <youjingxiaogao2@...il.com>
> ---
>  net/bluetooth/hci_conn.c | 6 +++---
>  net/bluetooth/hci_sync.c | 3 +++
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> index 0795818963a..aa3607327ad 100644
> --- a/net/bluetooth/hci_conn.c
> +++ b/net/bluetooth/hci_conn.c
> @@ -1232,15 +1232,15 @@ void hci_conn_del(struct hci_conn *conn)
>  	skb_queue_purge(&conn->data_q);
>  	skb_queue_purge(&conn->tx_q.queue);
>  
> +	/* Dequeue callbacks using connection pointer as data */
> +	hci_cmd_sync_dequeue(hdev, NULL, conn, NULL);
> +
>  	/* Remove the connection from the list and cleanup its remaining
>  	 * state. This is a separate function since for some cases like
>  	 * BT_CONNECT_SCAN we *only* want the cleanup part without the
>  	 * rest of hci_conn_del.
>  	 */
>  	hci_conn_cleanup(conn);
> -
> -	/* Dequeue callbacks using connection pointer as data */
> -	hci_cmd_sync_dequeue(hdev, NULL, conn, NULL);
>  }
>  
>  struct hci_dev *hci_get_route(bdaddr_t *dst, bdaddr_t *src, uint8_t src_type)
> diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> index f04a90bce4a..f31086c187f 100644
> --- a/net/bluetooth/hci_sync.c
> +++ b/net/bluetooth/hci_sync.c
> @@ -7371,6 +7371,9 @@ static void le_read_features_complete(struct hci_dev *hdev, void *data, int err)
>  	if (err == -ECANCELED)
>  		return;
>  
> +	if (!hci_conn_valid(hdev, conn))
> +		return;
> +
>  	hci_conn_drop(conn);
>  }
>  
> -- 
> 2.43.0
>
The uaf [1] is due to the following race,

	cpu1				cpu2
	hci_cmd_sync_work()		hci_rx_work()
	mutex_lock(&hdev->cmd_sync_work_lock);
	entry = list_first_entry_or_null(&hdev->cmd_sync_work_list,
					 struct hci_cmd_sync_work_entry,
					 list);
	if (entry)
		list_del(&entry->list);
	mutex_unlock(&hdev->cmd_sync_work_lock);

					hci_conn_del()
					hci_conn_hash_del(hdev, conn);
					hci_conn_cleanup(conn)	// free conn
					hci_cmd_sync_dequeue()
					mutex_lock(&hdev->cmd_sync_work_lock);
					while ((entry = _hci_cmd_sync_lookup_entry(hdev, func, data,
						   destroy))) {
						_hci_cmd_sync_cancel_entry(hdev, entry, -ECANCELED);
						ret = true;
					}
					mutex_unlock(&hdev->cmd_sync_work_lock);

	hci_req_sync_lock(hdev);
	err = entry->func(hdev, entry->data);
	if (entry->destroy)
		entry->destroy(hdev, entry->data, err);
		hci_conn_drop(conn)	// uaf
	hci_req_sync_unlock(hdev);

but the race still exists after this patch.

	cpu1				cpu2
	hci_conn_valid(hdev, conn)
					hci_conn_hash_del(hdev, conn);
					hci_cmd_sync_dequeue()
					hci_conn_cleanup(conn)	// free conn
	hci_conn_drop(conn); // uaf

[1] Subject: [syzbot] [bluetooth?] KASAN: slab-use-after-free Write in hci_conn_drop (3)
https://lore.kernel.org/lkml/69301edd.a70a0220.2ea503.00cf.GAE@google.com/