net: hdlc_fr: Add support for any Ethertype

Change the fr_rx function to make this driver support any Ethertype
when receiving skbs on normal (non-Ethernet-emulating) PVC devices.
(This driver is already able to handle any Ethertype when sending.)

Originally in the fr_rx function, the code that parses the long (10-byte)
header only recognizes a few Ethertype values and drops frames with other
Ethertype values. This patch replaces this code to make fr_rx support
any Ethertype. This patch also creates a new function fr_snap_parse as
part of the new code.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/wan/hdlc_fr.c

@@ -871,6 +871,45 @@ static int fr_lmi_recv(struct net_device *dev, struct sk_buff *skb)
 	return 0;
 }
 
+static int fr_snap_parse(struct sk_buff *skb, struct pvc_device *pvc)
+{
+	/* OUI 00-00-00 indicates an Ethertype follows */
+	if (skb->data[0] == 0x00 &&
+	    skb->data[1] == 0x00 &&
+	    skb->data[2] == 0x00) {
+		if (!pvc->main)
+			return -1;
+		skb->dev = pvc->main;
+		skb->protocol = *(__be16 *)(skb->data + 3); /* Ethertype */
+		skb_pull(skb, 5);
+		skb_reset_mac_header(skb);
+		return 0;
+
+	/* OUI 00-80-C2 stands for the 802.1 organization */
+	} else if (skb->data[0] == 0x00 &&
+		   skb->data[1] == 0x80 &&
+		   skb->data[2] == 0xC2) {
+		/* PID 00-07 stands for Ethernet frames without FCS */
+		if (skb->data[3] == 0x00 &&
+		    skb->data[4] == 0x07) {
+			if (!pvc->ether)
+				return -1;
+			skb_pull(skb, 5);
+			if (skb->len < ETH_HLEN)
+				return -1;
+			skb->protocol = eth_type_trans(skb, pvc->ether);
+			return 0;
+
+		/* PID unsupported */
+		} else {
+			return -1;
+		}
+
+	/* OUI unsupported */
+	} else {
+		return -1;
+	}
+}
 
 static int fr_rx(struct sk_buff *skb)
 {
@@ -945,35 +984,19 @@ static int fr_rx(struct sk_buff *skb)
 		skb->protocol = htons(ETH_P_IPV6);
 		skb_reset_mac_header(skb);
 
-	} else if (skb->len > 10 && data[3] == FR_PAD &&
-		   data[4] == NLPID_SNAP && data[5] == FR_PAD) {
-		u16 oui = ntohs(*(__be16*)(data + 6));
-		u16 pid = ntohs(*(__be16*)(data + 8));
-		skb_pull(skb, 10);
-
-		switch ((((u32)oui) << 16) | pid) {
-		case ETH_P_ARP: /* routed frame with SNAP */
-		case ETH_P_IPX:
-		case ETH_P_IP:	/* a long variant */
-		case ETH_P_IPV6:
-			if (!pvc->main)
-				goto rx_drop;
-			skb->dev = pvc->main;
-			skb->protocol = htons(pid);
-			skb_reset_mac_header(skb);
-			break;
-
-		case 0x80C20007: /* bridged Ethernet frame */
-			if (!pvc->ether)
+	} else if (data[3] == FR_PAD) {
+		if (skb->len < 5)
+			goto rx_error;
+		if (data[4] == NLPID_SNAP) { /* A SNAP header follows */
+			skb_pull(skb, 5);
+			if (skb->len < 5) /* Incomplete SNAP header */
+				goto rx_error;
+			if (fr_snap_parse(skb, pvc))
 				goto rx_drop;
-			skb->protocol = eth_type_trans(skb, pvc->ether);
-			break;
-
-		default:
-			netdev_info(frad, "Unsupported protocol, OUI=%x PID=%x\n",
-				    oui, pid);
+		} else {
 			goto rx_drop;
 		}
+
 	} else {
 		netdev_info(frad, "Unsupported protocol, NLPID=%x length=%i\n",
 			    data[3], skb->len);