/*
   *	IPV4 GSO/GRO offload support
   *	Linux INET implementation
   *
   *	This program is free software; you can redistribute it and/or
   *	modify it under the terms of the GNU General Public License
   *	as published by the Free Software Foundation; either version
   *	2 of the License, or (at your option) any later version.
   *
   *	GRE GSO support
   */
  
  #include <linux/skbuff.h>

  #include <linux/init.h>

  #include <net/protocol.h>
  #include <net/gre.h>

  static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
  				       netdev_features_t features)
  {

  	int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);

  	struct sk_buff *segs = ERR_PTR(-EINVAL);

  	u16 mac_offset = skb->mac_header;

  	__be16 protocol = skb->protocol;

  	u16 mac_len = skb->mac_len;
  	int gre_offset, outer_hlen;

  	bool need_csum, ufo, gso_partial;

  	if (!skb->encapsulation)
  		goto out;

  	if (unlikely(tnl_hlen < sizeof(struct gre_base_hdr)))

  		goto out;

  	if (unlikely(!pskb_may_pull(skb, tnl_hlen)))

  		goto out;

  	/* setup inner skb. */

  	skb->encapsulation = 0;

  	SKB_GSO_CB(skb)->encap_level = 0;

  	__skb_pull(skb, tnl_hlen);

  	skb_reset_mac_header(skb);
  	skb_set_network_header(skb, skb_inner_network_offset(skb));
  	skb->mac_len = skb_inner_network_offset(skb);

  	skb->protocol = skb->inner_protocol;

  	need_csum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_GRE_CSUM);
  	skb->encap_hdr_csum = need_csum;

  	ufo = !!(skb_shinfo(skb)->gso_type & SKB_GSO_UDP);

  	features &= skb->dev->hw_enc_features;

  	/* The only checksum offload we care about from here on out is the
  	 * outer one so strip the existing checksum feature flags based
  	 * on the fact that we will be computing our checksum in software.
  	 */
  	if (ufo) {
  		features &= ~NETIF_F_CSUM_MASK;
  		if (!need_csum)
  			features |= NETIF_F_HW_CSUM;
  	}

  	/* segment inner packet. */

  	segs = skb_mac_gso_segment(skb, features);

  	if (IS_ERR_OR_NULL(segs)) {

  		skb_gso_error_unwind(skb, protocol, tnl_hlen, mac_offset,
  				     mac_len);

  		goto out;

  	}

  	gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);

  	outer_hlen = skb_tnl_header_len(skb);
  	gre_offset = outer_hlen - tnl_hlen;

  	skb = segs;

  	do {

  		struct gre_base_hdr *greh;

  		__sum16 *pcsum;

  		/* Set up inner headers if we are offloading inner checksum */
  		if (skb->ip_summed == CHECKSUM_PARTIAL) {
  			skb_reset_inner_headers(skb);
  			skb->encapsulation = 1;
  		}

  		skb->mac_len = mac_len;
  		skb->protocol = protocol;

  
  		__skb_push(skb, outer_hlen);
  		skb_reset_mac_header(skb);
  		skb_set_network_header(skb, mac_len);
  		skb_set_transport_header(skb, gre_offset);
  
  		if (!need_csum)
  			continue;
  
  		greh = (struct gre_base_hdr *)skb_transport_header(skb);

  		pcsum = (__sum16 *)(greh + 1);

  		if (gso_partial) {

  			unsigned int partial_adj;
  
  			/* Adjust checksum to account for the fact that
  			 * the partial checksum is based on actual size
  			 * whereas headers should be based on MSS size.
  			 */
  			partial_adj = skb->len + skb_headroom(skb) -
  				      SKB_GSO_CB(skb)->data_offset -
  				      skb_shinfo(skb)->gso_size;
  			*pcsum = ~csum_fold((__force __wsum)htonl(partial_adj));
  		} else {
  			*pcsum = 0;
  		}

  		*(pcsum + 1) = 0;
  		*pcsum = gso_make_checksum(skb, 0);

  	} while ((skb = skb->next));
  out:
  	return segs;
  }

  static struct sk_buff **gre_gro_receive(struct sk_buff **head,
  					struct sk_buff *skb)
  {
  	struct sk_buff **pp = NULL;
  	struct sk_buff *p;
  	const struct gre_base_hdr *greh;
  	unsigned int hlen, grehlen;
  	unsigned int off;
  	int flush = 1;
  	struct packet_offload *ptype;
  	__be16 type;

  	if (NAPI_GRO_CB(skb)->encap_mark)
  		goto out;
  
  	NAPI_GRO_CB(skb)->encap_mark = 1;

  	off = skb_gro_offset(skb);
  	hlen = off + sizeof(*greh);
  	greh = skb_gro_header_fast(skb, off);
  	if (skb_gro_header_hard(skb, hlen)) {
  		greh = skb_gro_header_slow(skb, hlen, off);
  		if (unlikely(!greh))
  			goto out;
  	}
  
  	/* Only support version 0 and K (key), C (csum) flags. Note that
  	 * although the support for the S (seq#) flag can be added easily
  	 * for GRO, this is problematic for GSO hence can not be enabled
  	 * here because a GRO pkt may end up in the forwarding path, thus
  	 * requiring GSO support to break it up correctly.
  	 */
  	if ((greh->flags & ~(GRE_KEY|GRE_CSUM)) != 0)
  		goto out;

  	/* We can only support GRE_CSUM if we can track the location of
  	 * the GRE header.  In the case of FOU/GUE we cannot because the
  	 * outer UDP header displaces the GRE header leaving us in a state
  	 * of limbo.
  	 */
  	if ((greh->flags & GRE_CSUM) && NAPI_GRO_CB(skb)->is_fou)
  		goto out;

  	type = greh->protocol;
  
  	rcu_read_lock();
  	ptype = gro_find_receive_by_type(type);

  	if (!ptype)

  		goto out_unlock;
  
  	grehlen = GRE_HEADER_SECTION;
  
  	if (greh->flags & GRE_KEY)
  		grehlen += GRE_HEADER_SECTION;
  
  	if (greh->flags & GRE_CSUM)
  		grehlen += GRE_HEADER_SECTION;
  
  	hlen = off + grehlen;
  	if (skb_gro_header_hard(skb, hlen)) {
  		greh = skb_gro_header_slow(skb, hlen, off);
  		if (unlikely(!greh))
  			goto out_unlock;
  	}

  
  	/* Don't bother verifying checksum if we're going to flush anyway. */

  	if ((greh->flags & GRE_CSUM) && !NAPI_GRO_CB(skb)->flush) {
  		if (skb_gro_checksum_simple_validate(skb))

  			goto out_unlock;

  		skb_gro_checksum_try_convert(skb, IPPROTO_GRE, 0,
  					     null_compute_pseudo);
  	}

  	for (p = *head; p; p = p->next) {
  		const struct gre_base_hdr *greh2;
  
  		if (!NAPI_GRO_CB(p)->same_flow)
  			continue;
  
  		/* The following checks are needed to ensure only pkts
  		 * from the same tunnel are considered for aggregation.
  		 * The criteria for "the same tunnel" includes:
  		 * 1) same version (we only support version 0 here)
  		 * 2) same protocol (we only support ETH_P_IP for now)
  		 * 3) same set of flags
  		 * 4) same key if the key field is present.
  		 */
  		greh2 = (struct gre_base_hdr *)(p->data + off);
  
  		if (greh2->flags != greh->flags ||
  		    greh2->protocol != greh->protocol) {
  			NAPI_GRO_CB(p)->same_flow = 0;
  			continue;
  		}
  		if (greh->flags & GRE_KEY) {
  			/* compare keys */
  			if (*(__be32 *)(greh2+1) != *(__be32 *)(greh+1)) {
  				NAPI_GRO_CB(p)->same_flow = 0;
  				continue;
  			}
  		}
  	}
  
  	skb_gro_pull(skb, grehlen);
  
  	/* Adjusted NAPI_GRO_CB(skb)->csum after skb_gro_pull()*/
  	skb_gro_postpull_rcsum(skb, greh, grehlen);

  	pp = call_gro_receive(ptype->callbacks.gro_receive, head, skb);

  	flush = 0;

  
  out_unlock:
  	rcu_read_unlock();
  out:
  	NAPI_GRO_CB(skb)->flush |= flush;
  
  	return pp;
  }

  static int gre_gro_complete(struct sk_buff *skb, int nhoff)

  {
  	struct gre_base_hdr *greh = (struct gre_base_hdr *)(skb->data + nhoff);
  	struct packet_offload *ptype;
  	unsigned int grehlen = sizeof(*greh);
  	int err = -ENOENT;
  	__be16 type;

  	skb->encapsulation = 1;
  	skb_shinfo(skb)->gso_type = SKB_GSO_GRE;

  	type = greh->protocol;
  	if (greh->flags & GRE_KEY)
  		grehlen += GRE_HEADER_SECTION;
  
  	if (greh->flags & GRE_CSUM)
  		grehlen += GRE_HEADER_SECTION;
  
  	rcu_read_lock();
  	ptype = gro_find_complete_by_type(type);

  	if (ptype)

  		err = ptype->callbacks.gro_complete(skb, nhoff + grehlen);
  
  	rcu_read_unlock();

  
  	skb_set_inner_mac_header(skb, nhoff + grehlen);

  	return err;
  }

  static const struct net_offload gre_offload = {
  	.callbacks = {

  		.gso_segment = gre_gso_segment,

  		.gro_receive = gre_gro_receive,
  		.gro_complete = gre_gro_complete,

  	},
  };

  static int __init gre_offload_init(void)

  {

  	int err;
  
  	err = inet_add_offload(&gre_offload, IPPROTO_GRE);
  #if IS_ENABLED(CONFIG_IPV6)
  	if (err)
  		return err;
  
  	err = inet6_add_offload(&gre_offload, IPPROTO_GRE);
  	if (err)
  		inet_del_offload(&gre_offload, IPPROTO_GRE);
  #endif
  
  	return err;

  }

  device_initcall(gre_offload_init);