gre_offload: simplify GRE header length calculation in gre_gso_segment()

Simplify the GRE header length calculation in gre_gso_segment().
Switch to an approach that is simpler, faster, and more general. The
new approach will continue to be correct even if we add support for
the optional variable-length routing info that may be present in a GRE
header.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: H.K. Jerry Chu <hkchu@google.com>
Cc: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index 31da9f5125837d0af682cefee2869948680830cb..29512e3e7e7c6f598854d4d3eafd4e4047fc6440 100644 (file)
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -26,7 +26,7 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
 {
        struct sk_buff *segs = ERR_PTR(-EINVAL);
        netdev_features_t enc_features;
-       int ghl = GRE_HEADER_SECTION;
+       int ghl;
        struct gre_base_hdr *greh;
        u16 mac_offset = skb->mac_header;
        int mac_len = skb->mac_len;
@@ -49,15 +49,11 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
 
        greh = (struct gre_base_hdr *)skb_transport_header(skb);
 
-       if (greh->flags & GRE_KEY)
-               ghl += GRE_HEADER_SECTION;
-       if (greh->flags & GRE_SEQ)
-               ghl += GRE_HEADER_SECTION;
-       if (greh->flags & GRE_CSUM) {
-               ghl += GRE_HEADER_SECTION;
-               csum = true;
-       } else
-               csum = false;
+       ghl = skb_inner_network_header(skb) - skb_transport_header(skb);
+       if (unlikely(ghl < sizeof(*greh)))
+               goto out;
+
+       csum = !!(greh->flags & GRE_CSUM);
 
        if (unlikely(!pskb_may_pull(skb, ghl)))
                goto out;