On Thu, 30 Sep 2021 11:33:20 +0800, Zhang Changzhong wrote:
> According to SAE-J1939-21, the data length of TP.DT must be 8 bytes, so
> cancel session when receive unexpected TP.DT message.
SAE-j1939-21 indeed says that all TP.DT must be 8 bytes.
However, the last TP.DT may contain up to 6 stuff bytes, which have no meaning.
If I remember well, they are even not 'reserved'.
>
> Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
> Signed-off-by: Zhang Changzhong <zhangchangzhong@xxxxxxxxxx>
> ---
> net/can/j1939/transport.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
> index bb5c4b8..eedaeaf 100644
> --- a/net/can/j1939/transport.c
> +++ b/net/can/j1939/transport.c
> @@ -1789,6 +1789,7 @@ static void j1939_xtp_rx_dpo(struct j1939_priv *priv, struct sk_buff *skb,
> static void j1939_xtp_rx_dat_one(struct j1939_session *session,
> struct sk_buff *skb)
> {
> + enum j1939_xtp_abort abort = J1939_XTP_ABORT_FAULT;
> struct j1939_priv *priv = session->priv;
> struct j1939_sk_buff_cb *skcb, *se_skcb;
> struct sk_buff *se_skb = NULL;
> @@ -1803,9 +1804,11 @@ static void j1939_xtp_rx_dat_one(struct j1939_session *session,
>
> skcb = j1939_skb_to_cb(skb);
> dat = skb->data;
> - if (skb->len <= 1)
> + if (skb->len != 8) {
> /* makes no sense */
> + abort = J1939_XTP_ABORT_UNEXPECTED_DATA;
> goto out_session_cancel;
I think this is a situation of
"be strict on what you send, be tolerant on what you receive".
Did you find a technical reason to abort a session because the last frame didn't
bring overhead that you don't use?
Kind regards,
Kurt
> + }
>
> switch (session->last_cmd) {
> case 0xff:
> @@ -1904,7 +1907,7 @@ static void j1939_xtp_rx_dat_one(struct j1939_session *session,
> out_session_cancel:
> kfree_skb(se_skb);
> j1939_session_timers_cancel(session);
> - j1939_session_cancel(session, J1939_XTP_ABORT_FAULT);
> + j1939_session_cancel(session, abort);
> j1939_session_put(session);
> }
>
> --
> 2.9.5
>
