Re: [PATCH net-next 06/15] ipv6/gro: insert temporary HBH/jumbo header

From: Eric Dumazet <edumazet@google.com>

Following patch will add GRO_IPV6_MAX_SIZE, allowing gro to build
BIG TCP ipv6 packets (bigger than 64K).

This patch changes ipv6_gro_complete() to insert a HBH/jumbo header
so that resulting packet can go through IPv6/TCP stacks.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv6/ip6_offload.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
index d37a79a8554e92a1dcaa6fd023cafe2114841ece..dac6f60436e167a3d979fef02f25fc039c6ed37d 100644
--- a/net/ipv6/ip6_offload.c
+++ b/net/ipv6/ip6_offload.c

@@ -318,15 +318,43 @@ static struct sk_buff *ip4ip6_gro_receive(struct list_head *head,
 INDIRECT_CALLABLE_SCOPE int ipv6_gro_complete(struct sk_buff *skb, int nhoff)
 {
 	const struct net_offload *ops;
-	struct ipv6hdr *iph = (struct ipv6hdr *)(skb->data + nhoff);
+	struct ipv6hdr *iph;
 	int err = -ENOSYS;
+	u32 payload_len;
 
 	if (skb->encapsulation) {
 		skb_set_inner_protocol(skb, cpu_to_be16(ETH_P_IPV6));
 		skb_set_inner_network_header(skb, nhoff);
 	}
 
-	iph->payload_len = htons(skb->len - nhoff - sizeof(*iph));
+	payload_len = skb->len - nhoff - sizeof(*iph);
+	if (unlikely(payload_len > IPV6_MAXPLEN)) {
+		struct hop_jumbo_hdr *hop_jumbo;
+		int hoplen = sizeof(*hop_jumbo);
+
+		/* Move network header left */
+		memmove(skb_mac_header(skb) - hoplen, skb_mac_header(skb),
+			skb->transport_header - skb->mac_header);