/*
   *	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 int gre_gso_send_check(struct sk_buff *skb)
  {
  	if (!skb->encapsulation)
  		return -EINVAL;
  	return 0;
  }
  
  static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
  				       netdev_features_t features)
  {
  	struct sk_buff *segs = ERR_PTR(-EINVAL);
  	netdev_features_t enc_features;
  	int ghl;
  	struct gre_base_hdr *greh;
  	u16 mac_offset = skb->mac_header;
  	int mac_len = skb->mac_len;
  	__be16 protocol = skb->protocol;
  	int tnl_hlen;
  	bool csum;
  
  	if (unlikely(skb_shinfo(skb)->gso_type &
  				~(SKB_GSO_TCPV4 |
  				  SKB_GSO_TCPV6 |
  				  SKB_GSO_UDP |
  				  SKB_GSO_DODGY |
  				  SKB_GSO_TCP_ECN |
  				  SKB_GSO_GRE |
  				  SKB_GSO_IPIP)))
  		goto out;
  
  	if (unlikely(!pskb_may_pull(skb, sizeof(*greh))))
  		goto out;
  
  	greh = (struct gre_base_hdr *)skb_transport_header(skb);
  
  	ghl = skb_inner_mac_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;
  
  	/* setup inner skb. */
  	skb->protocol = greh->protocol;
  	skb->encapsulation = 0;
  
  	__skb_pull(skb, ghl);
  	skb_reset_mac_header(skb);
  	skb_set_network_header(skb, skb_inner_network_offset(skb));
  	skb->mac_len = skb_inner_network_offset(skb);
  
  	/* segment inner packet. */
  	enc_features = skb->dev->hw_enc_features & netif_skb_features(skb);
  	segs = skb_mac_gso_segment(skb, enc_features);
  	if (!segs || IS_ERR(segs)) {
  		skb_gso_error_unwind(skb, protocol, ghl, mac_offset, mac_len);
  		goto out;
  	}
  
  	skb = segs;
  	tnl_hlen = skb_tnl_header_len(skb);
  	do {
  		__skb_push(skb, ghl);
  		if (csum) {
  			__be32 *pcsum;
  
  			if (skb_has_shared_frag(skb)) {
  				int err;
  
  				err = __skb_linearize(skb);
  				if (err) {
  					kfree_skb_list(segs);
  					segs = ERR_PTR(err);
  					goto out;
  				}
  			}
  
  			greh = (struct gre_base_hdr *)(skb->data);
  			pcsum = (__be32 *)(greh + 1);
  			*pcsum = 0;
  			*(__sum16 *)pcsum = csum_fold(skb_checksum(skb, 0, skb->len, 0));
  		}
  		__skb_push(skb, tnl_hlen - ghl);
  
  		skb_reset_inner_headers(skb);
  		skb->encapsulation = 1;
  
  		skb_reset_mac_header(skb);
  		skb_set_network_header(skb, mac_len);
  		skb->mac_len = mac_len;
  		skb->protocol = protocol;
  	} while ((skb = skb->next));
  out:
  	return segs;
  }
  
  /* Compute the whole skb csum in s/w and store it, then verify GRO csum
   * starting from gro_offset.
   */
  static __sum16 gro_skb_checksum(struct sk_buff *skb)
  {
  	__sum16 sum;
  
  	skb->csum = skb_checksum(skb, 0, skb->len, 0);
  	NAPI_GRO_CB(skb)->csum = csum_sub(skb->csum,
  		csum_partial(skb->data, skb_gro_offset(skb), 0));
  	sum = csum_fold(NAPI_GRO_CB(skb)->csum);
  	if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE)) {
  		if (unlikely(!sum))
  			netdev_rx_csum_fault(skb->dev);
  	} else
  		skb->ip_summed = CHECKSUM_COMPLETE;
  
  	return sum;
  }
  
  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;
  
  	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;
  
  	type = greh->protocol;
  
  	rcu_read_lock();
  	ptype = gro_find_receive_by_type(type);
  	if (ptype == NULL)
  		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;
  	}
  	if (greh->flags & GRE_CSUM) { /* Need to verify GRE csum first */
  		__sum16 csum = 0;
  
  		if (skb->ip_summed == CHECKSUM_COMPLETE)
  			csum = csum_fold(NAPI_GRO_CB(skb)->csum);
  		/* Don't trust csum error calculated/reported by h/w */
  		if (skb->ip_summed == CHECKSUM_NONE || csum != 0)
  			csum = gro_skb_checksum(skb);
  
  		/* GRE CSUM is the 1's complement of the 1's complement sum
  		 * of the GRE hdr plus payload so it should add up to 0xffff
  		 * (and 0 after csum_fold()) just like the IPv4 hdr csum.
  		 */
  		if (csum)
  			goto out_unlock;
  	}
  	flush = 0;
  
  	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 = ptype->callbacks.gro_receive(head, skb);
  
  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 != NULL)
  		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_send_check = gre_gso_send_check,
  		.gso_segment = gre_gso_segment,
  		.gro_receive = gre_gro_receive,
  		.gro_complete = gre_gro_complete,
  	},
  };
  
  static int __init gre_offload_init(void)
  {
  	return inet_add_offload(&gre_offload, IPPROTO_GRE);
  }
  device_initcall(gre_offload_init);