net: ip_gre: use erspan key field for tunnel lookup

Use ERSPAN key header field as tunnel key in gre_parse_header routine
since ERSPAN protocol sets the key field of the external GRE header to
0 resulting in a tunnel lookup fail in ip6gre_err.
In addition remove key field parsing and pskb_may_pull check in
erspan_rcv and ip6erspan_rcv

Fixes: 5a963eb6 ("ip6_gre: Add ERSPAN native tunnel support")
Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/gre_demux.c

@@ -25,6 +25,7 @@
 #include <linux/spinlock.h>
 #include <net/protocol.h>
 #include <net/gre.h>
+#include <net/erspan.h>
 
 #include <net/icmp.h>
 #include <net/route.h>
@@ -119,6 +120,22 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 			hdr_len += 4;
 	}
 	tpi->hdr_len = hdr_len;
+
+	/* ERSPAN ver 1 and 2 protocol sets GRE key field
+	 * to 0 and sets the configured key in the
+	 * inner erspan header field
+	 */
+	if (greh->protocol == htons(ETH_P_ERSPAN) ||
+	    greh->protocol == htons(ETH_P_ERSPAN2)) {
+		struct erspan_base_hdr *ershdr;
+
+		if (!pskb_may_pull(skb, nhs + hdr_len + sizeof(*ershdr)))
+			return -EINVAL;
+
+		ershdr = (struct erspan_base_hdr *)options;
+		tpi->key = cpu_to_be32(get_session_id(ershdr));
+	}
+
 	return hdr_len;
 }
 EXPORT_SYMBOL(gre_parse_header);

net/ipv4/ip_gre.c

@@ -268,20 +268,11 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 	int len;
 
 	itn = net_generic(net, erspan_net_id);
-	len = gre_hdr_len + sizeof(*ershdr);
-
-	/* Check based hdr len */
-	if (unlikely(!pskb_may_pull(skb, len)))
-		return PACKET_REJECT;
 
 	iph = ip_hdr(skb);
 	ershdr = (struct erspan_base_hdr *)(skb->data + gre_hdr_len);
 	ver = ershdr->ver;
 
-	/* The original GRE header does not have key field,
-	 * Use ERSPAN 10-bit session ID as key.
-	 */
-	tpi->key = cpu_to_be32(get_session_id(ershdr));
 	tunnel = ip_tunnel_lookup(itn, skb->dev->ifindex,
 				  tpi->flags | TUNNEL_KEY,
 				  iph->saddr, iph->daddr, tpi->key);

net/ipv6/ip6_gre.c

@@ -534,13 +534,9 @@ static int ip6erspan_rcv(struct sk_buff *skb, int gre_hdr_len,
 	struct ip6_tnl *tunnel;
 	u8 ver;
 
-	if (unlikely(!pskb_may_pull(skb, sizeof(*ershdr))))
-		return PACKET_REJECT;
-
 	ipv6h = ipv6_hdr(skb);
 	ershdr = (struct erspan_base_hdr *)skb->data;
 	ver = ershdr->ver;
-	tpi->key = cpu_to_be32(get_session_id(ershdr));
 
 	tunnel = ip6gre_tunnel_lookup(skb->dev,
 				      &ipv6h->saddr, &ipv6h->daddr, tpi->key,