On 2021/10/8 19:00, Oleksij Rempel wrote:

On Fri, Oct 08, 2021 at 05:22:12PM +0800, Zhang Changzhong wrote:

quoted

Hi Kurt,
Sorry for the late reply.

On 2021/9/30 15:42, Kurt Van Dijck wrote:

quoted

On Thu, 30 Sep 2021 11:33:20 +0800, Zhang Changzhong wrote:

quoted

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'.

Agree, these bytes are meaningless for last TP.DT.

quoted

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Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Signed-off-by: Zhang Changzhong <redacted>
---
 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?

No technical reason. The only reason is that SAE-J1939-82 requires responder
to abort session if any TP.DT less than 8 bytes (section A.3.4, Row 7).

Do you mean: "BAM Transport: Ensure DUT discards BAM transport when
TP.DT data packets are not correct size" ... "Verify DUT discards the
BAM transport if any TP.DT data packet has less than 8 bytes"?

Yes.

Regards,
Changzhong

Regards,
Oleksij