linux-kernel - Re: [PATCH] Bluetooth: add missing checks in state transitions

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Date: Sun, 18 Feb 2024 20:16:42 -0500
From: Sungwoo Kim <iam@...g-woo.kim>
Cc: daveti@...due.edu, Marcel Holtmann <marcel@...tmann.org>, 
	Johan Hedberg <johan.hedberg@...il.com>, Luiz Augusto von Dentz <luiz.dentz@...il.com>, 
	linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: add missing checks in state transitions

Hello, could I ask for comments on this?

On Fri, Feb 9, 2024 at 2:06 AM Sungwoo Kim <iam@...g-woo.kim> wrote:
>
> When an l2cap channel receives L2CAP_CONN_RSP, it revives from BT_DISCONN
> to BT_CONFIG or BT_CONNECTED.
> It is very weird, violates the specification, and I cannot see any real
> usecase for this.
> Similar to this, the L2cap channel has six illegal state transitions:
>
> 1. BT_CONNECT2 -> BT_CONFIG by L2CAP_CONN_RSP
> 2. BT_CONNECT2 -> BT_CONNECTED by L2CAP_CONF_RSP
> 3. BT_CONNECT2 -> BT_DISCONN by L2CAP_CONF_RSP
> 4. BT_CONNECTED -> BT_CONFIG by L2CAP_CONN_RSP
> 5. BT_DISCONN -> BT_CONFIG by L2CAP_CONN_RSP
> 6. BT_DISCONN -> BT_CONNECTED by L2CAP_CONN_RSP
>
> This patch fixes 2, 3, 5, and 6 by adding checks.
> For 1 and 4, I will make an RFC for as it requires some refactoring.
>
> The detaild logs are described in here:
> https://lore.kernel.org/lkml/CAJNyHpKpDdps4=QHZ77zu4jfY-NNBcGUrw6UwjuBKfpuSuE__g@mail.gmail.com/
>
> Signed-off-by: Sungwoo Kim <iam@...g-woo.kim>
> ---
>  net/bluetooth/l2cap_core.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 60298975d..c5fa2b683 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -4339,6 +4339,14 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
>
>         l2cap_chan_lock(chan);
>
> +       switch (chan->state) {
> +       case BT_CLOSED:
> +       case BT_DISCONN:
> +               l2cap_chan_unlock(chan);
> +               l2cap_chan_put(chan);
> +               goto unlock;
> +       }
> +
>         switch (result) {
>         case L2CAP_CR_SUCCESS:
>                 if (__l2cap_get_chan_by_dcid(conn, dcid)) {
> @@ -4552,6 +4560,14 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn,
>         if (!chan)
>                 return 0;
>
> +       switch (chan->state) {
> +       case BT_CLOSED:
> +       case BT_CONNECT:
> +       case BT_CONNECT2:
> +       case BT_DISCONN:
> +               goto done;
> +       }
> +
>         switch (result) {
>         case L2CAP_CONF_SUCCESS:
>                 l2cap_conf_rfc_get(chan, rsp->data, len);
> --
> 2.25.1
>