[PATCH] net: Fix GRE RX to use skb_transport_header for GRE header offset

GRE assumes that the GRE header is at skb_network_header +
ip_hrdlen(skb). It is more general to use skb_transport_header
and this allows the possbility of inserting additional header
between IP and GRE (which is what we will done in Generic UDP
Encapsulation for GRE).

Signed-off-by: Tom Herbert <redacted>
---
 net/ipv4/gre_demux.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/gre_demux.c b/net/ipv4/gre_demux.c
index 7e0756d..4a7b5b2 100644
--- a/net/ipv4/gre_demux.c
+++ b/net/ipv4/gre_demux.c

@@ -98,7 +98,6 @@ EXPORT_SYMBOL_GPL(gre_build_header);
 static int parse_gre_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 			    bool *csum_err)
 {
-	unsigned int ip_hlen = ip_hdrlen(skb);
 	const struct gre_base_hdr *greh;
 	__be32 *options;
 	int hdr_len;

@@ -106,7 +105,7 @@ static int parse_gre_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 	if (unlikely(!pskb_may_pull(skb, sizeof(struct gre_base_hdr))))
 		return -EINVAL;
 
-	greh = (struct gre_base_hdr *)(skb_network_header(skb) + ip_hlen);
+	greh = (struct gre_base_hdr *)skb_transport_header(skb);
 	if (unlikely(greh->flags & (GRE_VERSION | GRE_ROUTING)))
 		return -EINVAL;
 

@@ -116,7 +115,7 @@ static int parse_gre_header(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 	if (!pskb_may_pull(skb, hdr_len))
 		return -EINVAL;
 
-	greh = (struct gre_base_hdr *)(skb_network_header(skb) + ip_hlen);
+	greh = (struct gre_base_hdr *)skb_transport_header(skb);
 	tpi->proto = greh->protocol;
 
 	options = (__be32 *)(greh + 1);

-- 
2.1.0.rc2.206.gedb03e5

On Mon, 2014-09-08 at 08:29 -0700, Tom Herbert wrote:

GRE assumes that the GRE header is at skb_network_header +
ip_hrdlen(skb). It is more general to use skb_transport_header
and this allows the possbility of inserting additional header
between IP and GRE (which is what we will done in Generic UDP
Encapsulation for GRE).

Signed-off-by: Tom Herbert <redacted>
---
 net/ipv4/gre_demux.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

I am always confused why you do not include prior Acked-by when you
repost same patch.

This forces me to add it again.

Note this should be a net-next patch, right ?

Acked-by: Eric Dumazet <edumazet@google.com>

On Mon, Sep 8, 2014 at 8:50 AM, Eric Dumazet [off-list ref] wrote:

On Mon, 2014-09-08 at 08:29 -0700, Tom Herbert wrote:

quoted

GRE assumes that the GRE header is at skb_network_header +
ip_hrdlen(skb). It is more general to use skb_transport_header
and this allows the possbility of inserting additional header
between IP and GRE (which is what we will done in Generic UDP
Encapsulation for GRE).

Signed-off-by: Tom Herbert <redacted>
---
 net/ipv4/gre_demux.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

I am always confused why you do not include prior Acked-by when you
repost same patch.

Sorry, I'll do that next time.

This forces me to add it again.

Note this should be a net-next patch, right ?

Yes.

Acked-by: Eric Dumazet <edumazet@google.com>

From: Tom Herbert <redacted>
Date: Mon,  8 Sep 2014 08:29:12 -0700

GRE assumes that the GRE header is at skb_network_header +
ip_hrdlen(skb). It is more general to use skb_transport_header
and this allows the possbility of inserting additional header
between IP and GRE (which is what we will done in Generic UDP
Encapsulation for GRE).

Signed-off-by: Tom Herbert <redacted>

Applied, thanks Tom.