net: qualcomm: rmnet: Handle command packets with checksum trailer

When using the MAPv4 packet format in conjunction with MAP commands,
a dummy DL checksum trailer will be appended to the packet. Before
this packet is sent out as an ACK, the DL checksum trailer needs to be
removed.
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c

@@ -58,11 +58,24 @@ static u8 rmnet_map_do_flow_control(struct sk_buff *skb,
 }
 
 static void rmnet_map_send_ack(struct sk_buff *skb,
-			       unsigned char type)
+			       unsigned char type,
+			       struct rmnet_port *port)
 {
 	struct rmnet_map_control_command *cmd;
 	int xmit_status;
 
+	if (port->data_format & RMNET_INGRESS_FORMAT_MAP_CKSUMV4) {
+		if (skb->len < sizeof(struct rmnet_map_header) +
+		    RMNET_MAP_GET_LENGTH(skb) +
+		    sizeof(struct rmnet_map_dl_csum_trailer)) {
+			kfree_skb(skb);
+			return;
+		}
+
+		skb_trim(skb, skb->len -
+			 sizeof(struct rmnet_map_dl_csum_trailer));
+	}
+
 	skb->protocol = htons(ETH_P_MAP);
 
 	cmd = RMNET_MAP_GET_CMD_START(skb);
@@ -100,5 +113,5 @@ void rmnet_map_command(struct sk_buff *skb, struct rmnet_port *port)
 		break;
 	}
 	if (rc == RMNET_MAP_COMMAND_ACK)
-		rmnet_map_send_ack(skb, rc);
+		rmnet_map_send_ack(skb, rc, port);
 }