[PATCH net v2 3/3] can: j1939: j1939_tp_cmd_recv(): check the dst address of TP.CM_BAM

[Zhang Changzhong]

The TP.CM_BAM message must be sent to the global address [1], so add a
check to drop TP.CM_BAM sent to a non-global address.

Without this patch, the receiver will treat the following packets as
normal RTS/CTS tranport:
18EC0102#20090002FF002301
18EB0102#0100000000000000
18EB0102#020000FFFFFFFFFF

[1] SAE-J1939-82 2015 A.3.3 Row 1.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Signed-off-by: Zhang Changzhong <zhangchangzhong@xxxxxxxxxx>
---
 net/can/j1939/transport.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
index 05eb3d0..a271688 100644
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -2023,6 +2023,11 @@ static void j1939_tp_cmd_recv(struct j1939_priv *priv, struct sk_buff *skb)
 		extd = J1939_ETP;
 		fallthrough;
 	case J1939_TP_CMD_BAM:
+		if (cmd == J1939_TP_CMD_BAM && !j1939_cb_is_broadcast(skcb)) {
+			netdev_err_once(priv->ndev, "%s: BAM to unicast (%02x), ignoring!\n",
+					__func__, skcb->addr.sa);
+			return;
+		}
 		fallthrough;
 	case J1939_TP_CMD_RTS:
 		if (skcb->addr.type != extd)
-- 
2.9.5