linux-kernel - Re: [RFC PATCH] Bluetooth: hci_event: Ignore multiple conn complete events

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Date:   Fri, 21 Jan 2022 19:22:10 +0100
From:   Sönke Huster <soenke.huster@...oes.de>
To:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] Bluetooth: hci_event: Ignore multiple conn complete
 events

I just noticed that just checking for handle does not work, as obviously 0x0 could also be a handle value and therefore it can't be distinguished, whether it is not set yet or it is 0x0.

On 21.01.22 18:36, Soenke Huster wrote:
> When a HCI_CONNECTION_COMPLETE event is received multiple times
> for the same handle, the device is registered multiple times which leads
> to memory corruptions. Therefore, consequent events for a single
> connection are ignored.
> 
> The conn->state can hold different values so conn->handle is
> checked to detect whether a connection is already set up.
> 
> Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=215497
> Signed-off-by: Soenke Huster <soenke.huster@...oes.de>
> ---
> This fixes the referenced bug and several use-after-free issues I discovered.
> I tagged it as RFC, as I am not 100% sure if checking the existence of the
> handle is the correct approach, but to the best of my knowledge it must be
> set for the first time in this function for valid connections of this event,
> therefore it should be fine.
> 
> net/bluetooth/hci_event.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> index 681c623aa380..71ccb12c928d 100644
> --- a/net/bluetooth/hci_event.c
> +++ b/net/bluetooth/hci_event.c
> @@ -3106,6 +3106,17 @@ static void hci_conn_complete_evt(struct hci_dev *hdev, void *data,
>  		}
>  	}
>  
> +	/* The HCI_Connection_Complete event is only sent once per connection.
> +	 * Processing it more than once per connection can corrupt kernel memory.
> +	 *
> +	 * As the connection handle is set here for the first time, it indicates
> +	 * whether the connection is already set up.
> +	 */
> +	if (conn->handle) {
> +		bt_dev_err(hdev, "Ignoring HCI_Connection_Complete for existing connection");
> +		goto unlock;
> +	}
> +
>  	if (!ev->status) {
>  		conn->handle = __le16_to_cpu(ev->handle);
>