gre: change gre_parse_header to return the header length

It's easier for gre_parse_header to return the header length instead of
filing it into a parameter. That way, the callers that don't care about the
header length can just check whether the returned value is lower than zero.

In gre_err, the tunnel header must not be pulled. See commit b7f8fe25
("gre: do not pull header in ICMP error processing") for details.

This patch reduces the conflict between the mentioned commit and commit
95f5c64c ("gre: Move utility functions to common headers").
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Acked-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/gre.h

@@ -26,7 +26,7 @@ int gre_del_protocol(const struct gre_protocol *proto, u8 version);
 struct net_device *gretap_fb_dev_create(struct net *net, const char *name,
 				       u8 name_assign_type);
 int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
-		     bool *csum_err, int *hdr_len);
+		     bool *csum_err);
 
 static inline int gre_calc_hlen(__be16 o_flags)
 {

net/ipv4/gre_demux.c

@@ -60,8 +60,9 @@ int gre_del_protocol(const struct gre_protocol *proto, u8 version)
 }
 EXPORT_SYMBOL_GPL(gre_del_protocol);
 
+/* Fills in tpi and returns header length to be pulled. */
 int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
-		     bool *csum_err, int *ret_hdr_len)
+		     bool *csum_err)
 {
 	const struct gre_base_hdr *greh;
 	__be32 *options;
@@ -119,8 +120,7 @@ int gre_parse_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 				return -EINVAL;
 		}
 	}
-	*ret_hdr_len = hdr_len;
-	return 0;
+	return hdr_len;
 }
 EXPORT_SYMBOL(gre_parse_header);
 

net/ipv4/ip_gre.c

@@ -221,16 +221,12 @@ static void gre_err(struct sk_buff *skb, u32 info)
 	const int code = icmp_hdr(skb)->code;
 	struct tnl_ptk_info tpi;
 	bool csum_err = false;
-	int hdr_len;
 
-	if (gre_parse_header(skb, &tpi, &csum_err, &hdr_len)) {
+	if (gre_parse_header(skb, &tpi, &csum_err) < 0) {
 		if (!csum_err)		/* ignore csum errors. */
 			return;
 	}
 
-	if (iptunnel_pull_header(skb, hdr_len, tpi.proto, false))
-		return;
-
 	if (type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED) {
 		ipv4_update_pmtu(skb, dev_net(skb->dev), info,
 				 skb->dev->ifindex, 0, IPPROTO_GRE, 0);
@@ -314,7 +310,8 @@ static int gre_rcv(struct sk_buff *skb)
 	}
 #endif
 
-	if (gre_parse_header(skb, &tpi, &csum_err, &hdr_len) < 0)
+	hdr_len = gre_parse_header(skb, &tpi, &csum_err);
+	if (hdr_len < 0)
 		goto drop;
 
 	if (iptunnel_pull_header(skb, hdr_len, tpi.proto, false))

net/ipv6/ip6_gre.c

@@ -468,7 +468,8 @@ static int gre_rcv(struct sk_buff *skb)
 	bool csum_err = false;
 	int hdr_len;
 
-	if (gre_parse_header(skb, &tpi, &csum_err, &hdr_len) < 0)
+	hdr_len = gre_parse_header(skb, &tpi, &csum_err);
+	if (hdr_len < 0)
 		goto drop;
 
 	if (iptunnel_pull_header(skb, hdr_len, tpi.proto, false))