[PATCH net] can: j1939: j1939_xtp_rx_rts_session_new(): abort TP less than 9 bytes

[Zhang Changzhong]

The receiver should abort TP if 'total message size' in TP.CM_RTS and
TP.CM_BAM is less than 9 or greater than 1785 [1], but currently the
j1939 stack only checks the upper bound and the receiver will accept the
following broadcast message:
  vcan1  18ECFF00   [8]  20 08 00 02 FF 00 23 01
  vcan1  18EBFF00   [8]  01 00 00 00 00 00 00 00
  vcan1  18EBFF00   [8]  02 00 FF FF FF FF FF FF

This patch adds check for the lower bound and abort illegal TP.

[1] SAE-J1939-82 A.3.4 Row 2 and A.3.6 Row 6.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Signed-off-by: Zhang Changzhong <zhangchangzhong@xxxxxxxxxx>
---
 net/can/j1939/j1939-priv.h | 1 +
 net/can/j1939/transport.c  | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/net/can/j1939/j1939-priv.h b/net/can/j1939/j1939-priv.h
index f6df208..16af1a7 100644
--- a/net/can/j1939/j1939-priv.h
+++ b/net/can/j1939/j1939-priv.h
@@ -330,6 +330,7 @@ int j1939_session_activate(struct j1939_session *session);
 void j1939_tp_schedule_txtimer(struct j1939_session *session, int msec);
 void j1939_session_timers_cancel(struct j1939_session *session);
 
+#define J1939_MIN_TP_PACKET_SIZE 9
 #define J1939_MAX_TP_PACKET_SIZE (7 * 0xff)
 #define J1939_MAX_ETP_PACKET_SIZE (7 * 0x00ffffff)
 
diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
index bb5c4b8..b685d31 100644
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -1609,6 +1609,8 @@ j1939_session *j1939_xtp_rx_rts_session_new(struct j1939_priv *priv,
 			abort = J1939_XTP_ABORT_FAULT;
 		else if (len > priv->tp_max_packet_size)
 			abort = J1939_XTP_ABORT_RESOURCE;
+		else if (len < J1939_MIN_TP_PACKET_SIZE)
+			abort = J1939_XTP_ABORT_FAULT;
 	}
 
 	if (abort != J1939_XTP_NO_ABORT) {
-- 
2.9.5