net/ipv4/udp_offload.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *	IPV4 GSO/GRO offload support
  *	Linux INET implementation
  *
  *	UDPv4 GSO support
  */

 #include <linux/skbuff.h>
 #include <net/udp.h>
 #include <net/protocol.h>
 #include <net/inet_common.h>

 static struct sk_buff *__skb_udp_tunnel_segment(struct sk_buff *skb,
 	netdev_features_t features,
 	struct sk_buff *(*gso_inner_segment)(struct sk_buff *skb,
 					     netdev_features_t features),
 	__be16 new_protocol, bool is_ipv6)
 {
 	int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);
 	bool remcsum, need_csum, offload_csum, gso_partial;
 	struct sk_buff *segs = ERR_PTR(-EINVAL);
 	struct udphdr *uh = udp_hdr(skb);
 	u16 mac_offset = skb->mac_header;
 	__be16 protocol = skb->protocol;
 	u16 mac_len = skb->mac_len;
 	int udp_offset, outer_hlen;
 	__wsum partial;
 	bool need_ipsec;

 	if (unlikely(!pskb_may_pull(skb, tnl_hlen)))
 		goto out;

 	/* Adjust partial header checksum to negate old length.
 	 * We cannot rely on the value contained in uh->len as it is
 	 * possible that the actual value exceeds the boundaries of the
 	 * 16 bit length field due to the header being added outside of an
 	 * IP or IPv6 frame that was already limited to 64K - 1.
 	 */
 	if (skb_shinfo(skb)->gso_type & SKB_GSO_PARTIAL)
 		partial = (__force __wsum)uh->len;
 	else
 		partial = (__force __wsum)htonl(skb->len);
 	partial = csum_sub(csum_unfold(uh->check), partial);

 	/* 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_set_transport_header(skb, skb_inner_transport_offset(skb));
 	skb->mac_len = skb_inner_network_offset(skb);
 	skb->protocol = new_protocol;

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

 	remcsum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_TUNNEL_REMCSUM);
 	skb->remcsum_offload = remcsum;

 	need_ipsec = skb_dst(skb) && dst_xfrm(skb_dst(skb));
 	/* Try to offload checksum if possible */
 	offload_csum = !!(need_csum &&
 			  !need_ipsec &&
 			  (skb->dev->features &
 			   (is_ipv6 ? (NETIF_F_HW_CSUM | NETIF_F_IPV6_CSUM) :
 				      (NETIF_F_HW_CSUM | NETIF_F_IP_CSUM))));

 	features &= skb->dev->hw_enc_features;
 	if (need_csum)
 		features &= ~NETIF_F_SCTP_CRC;

 	/* The only checksum offload we care about from here on out is the
 	 * outer one so strip the existing checksum feature flags and
 	 * instead set the flag based on our outer checksum offload value.
 	 */
 	if (remcsum) {
 		features &= ~NETIF_F_CSUM_MASK;
 		if (!need_csum || offload_csum)
 			features |= NETIF_F_HW_CSUM;
 	}

 	/* segment inner packet. */
 	segs = gso_inner_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);
 	udp_offset = outer_hlen - tnl_hlen;
 	skb = segs;
 	do {
 		unsigned int len;

 		if (remcsum)
 			skb->ip_summed = CHECKSUM_NONE;

 		/* 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, udp_offset);
 		len = skb->len - udp_offset;
 		uh = udp_hdr(skb);

 		/* If we are only performing partial GSO the inner header
 		 * will be using a length value equal to only one MSS sized
 		 * segment instead of the entire frame.
 		 */
 		if (gso_partial && skb_is_gso(skb)) {
 			uh->len = htons(skb_shinfo(skb)->gso_size +
 					SKB_GSO_CB(skb)->data_offset +
 					skb->head - (unsigned char *)uh);
 		} else {
 			uh->len = htons(len);
 		}

 		if (!need_csum)
 			continue;

 		uh->check = ~csum_fold(csum_add(partial,
 				       (__force __wsum)htonl(len)));

 		if (skb->encapsulation || !offload_csum) {
 			uh->check = gso_make_checksum(skb, ~uh->check);
 			if (uh->check == 0)
 				uh->check = CSUM_MANGLED_0;
 		} else {
 			skb->ip_summed = CHECKSUM_PARTIAL;
 			skb->csum_start = skb_transport_header(skb) - skb->head;
 			skb->csum_offset = offsetof(struct udphdr, check);
 		}
 	} while ((skb = skb->next));
 out:
 	return segs;
 }

 struct sk_buff *skb_udp_tunnel_segment(struct sk_buff *skb,
 				       netdev_features_t features,
 				       bool is_ipv6)
 {
 	__be16 protocol = skb->protocol;
 	const struct net_offload **offloads;
 	const struct net_offload *ops;
 	struct sk_buff *segs = ERR_PTR(-EINVAL);
 	struct sk_buff *(*gso_inner_segment)(struct sk_buff *skb,
 					     netdev_features_t features);

 	rcu_read_lock();

 	switch (skb->inner_protocol_type) {
 	case ENCAP_TYPE_ETHER:
 		protocol = skb->inner_protocol;
 		gso_inner_segment = skb_mac_gso_segment;
 		break;
 	case ENCAP_TYPE_IPPROTO:
 		offloads = is_ipv6 ? inet6_offloads : inet_offloads;
 		ops = rcu_dereference(offloads[skb->inner_ipproto]);
 		if (!ops || !ops->callbacks.gso_segment)
 			goto out_unlock;
 		gso_inner_segment = ops->callbacks.gso_segment;
 		break;
 	default:
 		goto out_unlock;
 	}

 	segs = __skb_udp_tunnel_segment(skb, features, gso_inner_segment,
 					protocol, is_ipv6);

 out_unlock:
 	rcu_read_unlock();

 	return segs;
 }
 EXPORT_SYMBOL(skb_udp_tunnel_segment);

 static void __udpv4_gso_segment_csum(struct sk_buff *seg,
 				     __be32 *oldip, __be32 *newip,
 				     __be16 *oldport, __be16 *newport)
 {
 	struct udphdr *uh;
 	struct iphdr *iph;

 	if (*oldip == *newip && *oldport == *newport)
 		return;

 	uh = udp_hdr(seg);
 	iph = ip_hdr(seg);

 	if (uh->check) {
 		inet_proto_csum_replace4(&uh->check, seg, *oldip, *newip,
 					 true);
 		inet_proto_csum_replace2(&uh->check, seg, *oldport, *newport,
 					 false);
 		if (!uh->check)
 			uh->check = CSUM_MANGLED_0;
 	}
 	*oldport = *newport;

 	csum_replace4(&iph->check, *oldip, *newip);
 	*oldip = *newip;
 }

 static struct sk_buff *__udpv4_gso_segment_list_csum(struct sk_buff *segs)
 {
 	struct sk_buff *seg;
 	struct udphdr *uh, *uh2;
 	struct iphdr *iph, *iph2;

 	seg = segs;
 	uh = udp_hdr(seg);
 	iph = ip_hdr(seg);

 	if ((udp_hdr(seg)->dest == udp_hdr(seg->next)->dest) &&
 	    (udp_hdr(seg)->source == udp_hdr(seg->next)->source) &&
 	    (ip_hdr(seg)->daddr == ip_hdr(seg->next)->daddr) &&
 	    (ip_hdr(seg)->saddr == ip_hdr(seg->next)->saddr))
 		return segs;

 	while ((seg = seg->next)) {
 		uh2 = udp_hdr(seg);
 		iph2 = ip_hdr(seg);

 		__udpv4_gso_segment_csum(seg,
 					 &iph2->saddr, &iph->saddr,
 					 &uh2->source, &uh->source);
 		__udpv4_gso_segment_csum(seg,
 					 &iph2->daddr, &iph->daddr,
 					 &uh2->dest, &uh->dest);
 	}

 	return segs;
 }

 static struct sk_buff *__udp_gso_segment_list(struct sk_buff *skb,
 					      netdev_features_t features,
 					      bool is_ipv6)
 {
 	unsigned int mss = skb_shinfo(skb)->gso_size;

 	skb = skb_segment_list(skb, features, skb_mac_header_len(skb));
 	if (IS_ERR(skb))
 		return skb;

 	udp_hdr(skb)->len = htons(sizeof(struct udphdr) + mss);

 	return is_ipv6 ? skb : __udpv4_gso_segment_list_csum(skb);
 }

 struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 				  netdev_features_t features, bool is_ipv6)
 {
 	struct sock *sk = gso_skb->sk;
 	unsigned int sum_truesize = 0;
 	struct sk_buff *segs, *seg;
 	struct udphdr *uh;
 	unsigned int mss;
 	bool copy_dtor;
 	__sum16 check;
 	__be16 newlen;

 	if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST)
 		return __udp_gso_segment_list(gso_skb, features, is_ipv6);

 	mss = skb_shinfo(gso_skb)->gso_size;
 	if (gso_skb->len <= sizeof(*uh) + mss)
 		return ERR_PTR(-EINVAL);

 	skb_pull(gso_skb, sizeof(*uh));

 	/* clear destructor to avoid skb_segment assigning it to tail */
 	copy_dtor = gso_skb->destructor == sock_wfree;
 	if (copy_dtor)
 		gso_skb->destructor = NULL;

 	segs = skb_segment(gso_skb, features);
 	if (IS_ERR_OR_NULL(segs)) {
 		if (copy_dtor)
 			gso_skb->destructor = sock_wfree;
 		return segs;
 	}

 	/* GSO partial and frag_list segmentation only requires splitting
 	 * the frame into an MSS multiple and possibly a remainder, both
 	 * cases return a GSO skb. So update the mss now.
 	 */
 	if (skb_is_gso(segs))
 		mss *= skb_shinfo(segs)->gso_segs;

 	seg = segs;
 	uh = udp_hdr(seg);

 	/* preserve TX timestamp flags and TS key for first segment */
 	skb_shinfo(seg)->tskey = skb_shinfo(gso_skb)->tskey;
 	skb_shinfo(seg)->tx_flags |=
 			(skb_shinfo(gso_skb)->tx_flags & SKBTX_ANY_TSTAMP);

 	/* compute checksum adjustment based on old length versus new */
 	newlen = htons(sizeof(*uh) + mss);
 	check = csum16_add(csum16_sub(uh->check, uh->len), newlen);

 	for (;;) {
 		if (copy_dtor) {
 			seg->destructor = sock_wfree;
 			seg->sk = sk;
 			sum_truesize += seg->truesize;
 		}

 		if (!seg->next)
 			break;

 		uh->len = newlen;
 		uh->check = check;

 		if (seg->ip_summed == CHECKSUM_PARTIAL)
 			gso_reset_checksum(seg, ~check);
 		else
 			uh->check = gso_make_checksum(seg, ~check) ? :
 				    CSUM_MANGLED_0;

 		seg = seg->next;
 		uh = udp_hdr(seg);
 	}

 	/* last packet can be partial gso_size, account for that in checksum */
 	newlen = htons(skb_tail_pointer(seg) - skb_transport_header(seg) +
 		       seg->data_len);
 	check = csum16_add(csum16_sub(uh->check, uh->len), newlen);

 	uh->len = newlen;
 	uh->check = check;

 	if (seg->ip_summed == CHECKSUM_PARTIAL)
 		gso_reset_checksum(seg, ~check);
 	else
 		uh->check = gso_make_checksum(seg, ~check) ? : CSUM_MANGLED_0;

 	/* update refcount for the packet */
 	if (copy_dtor) {
 		int delta = sum_truesize - gso_skb->truesize;

 		/* In some pathological cases, delta can be negative.
 		 * We need to either use refcount_add() or refcount_sub_and_test()
 		 */
 		if (likely(delta >= 0))
 			refcount_add(delta, &sk->sk_wmem_alloc);
 		else
 			WARN_ON_ONCE(refcount_sub_and_test(-delta, &sk->sk_wmem_alloc));
 	}
 	return segs;
 }
 EXPORT_SYMBOL_GPL(__udp_gso_segment);

 static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 					 netdev_features_t features)
 {
 	struct sk_buff *segs = ERR_PTR(-EINVAL);
 	unsigned int mss;
 	__wsum csum;
 	struct udphdr *uh;
 	struct iphdr *iph;

 	if (skb->encapsulation &&
 	    (skb_shinfo(skb)->gso_type &
 	     (SKB_GSO_UDP_TUNNEL|SKB_GSO_UDP_TUNNEL_CSUM))) {
 		segs = skb_udp_tunnel_segment(skb, features, false);
 		goto out;
 	}

 	if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_UDP | SKB_GSO_UDP_L4)))
 		goto out;

 	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 		goto out;

 	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
 		return __udp_gso_segment(skb, features, false);

 	mss = skb_shinfo(skb)->gso_size;
 	if (unlikely(skb->len <= mss))
 		goto out;

 	/* Do software UFO. Complete and fill in the UDP checksum as
 	 * HW cannot do checksum of UDP packets sent as multiple
 	 * IP fragments.
 	 */

 	uh = udp_hdr(skb);
 	iph = ip_hdr(skb);

 	uh->check = 0;
 	csum = skb_checksum(skb, 0, skb->len, 0);
 	uh->check = udp_v4_check(skb->len, iph->saddr, iph->daddr, csum);
 	if (uh->check == 0)
 		uh->check = CSUM_MANGLED_0;

 	skb->ip_summed = CHECKSUM_UNNECESSARY;

 	/* If there is no outer header we can fake a checksum offload
 	 * due to the fact that we have already done the checksum in
 	 * software prior to segmenting the frame.
 	 */
 	if (!skb->encap_hdr_csum)
 		features |= NETIF_F_HW_CSUM;

 	/* Fragment the skb. IP headers of the fragments are updated in
 	 * inet_gso_segment()
 	 */
 	segs = skb_segment(skb, features);
 out:
 	return segs;
 }

 #define UDP_GRO_CNT_MAX 64
 static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
 					       struct sk_buff *skb)
 {
 	struct udphdr *uh = udp_gro_udphdr(skb);
 	struct sk_buff *pp = NULL;
 	struct udphdr *uh2;
 	struct sk_buff *p;
 	unsigned int ulen;
 	int ret = 0;

 	/* requires non zero csum, for symmetry with GSO */
 	if (!uh->check) {
 		NAPI_GRO_CB(skb)->flush = 1;
 		return NULL;
 	}

 	/* Do not deal with padded or malicious packets, sorry ! */
 	ulen = ntohs(uh->len);
 	if (ulen <= sizeof(*uh) || ulen != skb_gro_len(skb)) {
 		NAPI_GRO_CB(skb)->flush = 1;
 		return NULL;
 	}
 	/* pull encapsulating udp header */
 	skb_gro_pull(skb, sizeof(struct udphdr));

 	list_for_each_entry(p, head, list) {
 		if (!NAPI_GRO_CB(p)->same_flow)
 			continue;

 		uh2 = udp_hdr(p);

 		/* Match ports only, as csum is always non zero */
 		if ((*(u32 *)&uh->source != *(u32 *)&uh2->source)) {
 			NAPI_GRO_CB(p)->same_flow = 0;
 			continue;
 		}

 		if (NAPI_GRO_CB(skb)->is_flist != NAPI_GRO_CB(p)->is_flist) {
 			NAPI_GRO_CB(skb)->flush = 1;
 			return p;
 		}

 		/* Terminate the flow on len mismatch or if it grow "too much".
 		 * Under small packet flood GRO count could elsewhere grow a lot
 		 * leading to excessive truesize values.
 		 * On len mismatch merge the first packet shorter than gso_size,
 		 * otherwise complete the GRO packet.
 		 */
 		if (ulen > ntohs(uh2->len)) {
 			pp = p;
 		} else {
 			if (NAPI_GRO_CB(skb)->is_flist) {
 				if (!pskb_may_pull(skb, skb_gro_offset(skb))) {
 					NAPI_GRO_CB(skb)->flush = 1;
 					return NULL;
 				}
 				if ((skb->ip_summed != p->ip_summed) ||
 				    (skb->csum_level != p->csum_level)) {
 					NAPI_GRO_CB(skb)->flush = 1;
 					return NULL;
 				}
 				ret = skb_gro_receive_list(p, skb);
 			} else {
 				skb_gro_postpull_rcsum(skb, uh,
 						       sizeof(struct udphdr));

 				ret = skb_gro_receive(p, skb);
 			}
 		}

 		if (ret || ulen != ntohs(uh2->len) ||
 		    NAPI_GRO_CB(p)->count >= UDP_GRO_CNT_MAX)
 			pp = p;

 		return pp;
 	}

 	/* mismatch, but we never need to flush */
 	return NULL;
 }

 struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,
 				struct udphdr *uh, struct sock *sk)
 {
 	struct sk_buff *pp = NULL;
 	struct sk_buff *p;
 	struct udphdr *uh2;
 	unsigned int off = skb_gro_offset(skb);
 	int flush = 1;

 	/* we can do L4 aggregation only if the packet can't land in a tunnel
 	 * otherwise we could corrupt the inner stream
 	 */
 	NAPI_GRO_CB(skb)->is_flist = 0;
 	if (!sk || !udp_sk(sk)->gro_receive) {
 		if (skb->dev->features & NETIF_F_GRO_FRAGLIST)
 			NAPI_GRO_CB(skb)->is_flist = sk ? !udp_sk(sk)->gro_enabled : 1;

 		if ((!sk && (skb->dev->features & NETIF_F_GRO_UDP_FWD)) ||
 		    (sk && udp_sk(sk)->gro_enabled) || NAPI_GRO_CB(skb)->is_flist)
 			pp = call_gro_receive(udp_gro_receive_segment, head, skb);
 		return pp;
 	}

 	if (NAPI_GRO_CB(skb)->encap_mark ||
 	    (uh->check && skb->ip_summed != CHECKSUM_PARTIAL &&
 	     NAPI_GRO_CB(skb)->csum_cnt == 0 &&
 	     !NAPI_GRO_CB(skb)->csum_valid))
 		goto out;

 	/* mark that this skb passed once through the tunnel gro layer */
 	NAPI_GRO_CB(skb)->encap_mark = 1;

 	flush = 0;

 	list_for_each_entry(p, head, list) {
 		if (!NAPI_GRO_CB(p)->same_flow)
 			continue;

 		uh2 = (struct udphdr   *)(p->data + off);

 		/* Match ports and either checksums are either both zero
 		 * or nonzero.
 		 */
 		if ((*(u32 *)&uh->source != *(u32 *)&uh2->source) ||
 		    (!uh->check ^ !uh2->check)) {
 			NAPI_GRO_CB(p)->same_flow = 0;
 			continue;
 		}
 	}

 	skb_gro_pull(skb, sizeof(struct udphdr)); /* pull encapsulating udp header */
 	skb_gro_postpull_rcsum(skb, uh, sizeof(struct udphdr));
 	pp = call_gro_receive_sk(udp_sk(sk)->gro_receive, sk, head, skb);

 out:
 	skb_gro_flush_final(skb, pp, flush);
 	return pp;
 }
 EXPORT_SYMBOL(udp_gro_receive);

 static struct sock *udp4_gro_lookup_skb(struct sk_buff *skb, __be16 sport,
 					__be16 dport)
 {
 	const struct iphdr *iph = skb_gro_network_header(skb);

 	return __udp4_lib_lookup(dev_net(skb->dev), iph->saddr, sport,
 				 iph->daddr, dport, inet_iif(skb),
 				 inet_sdif(skb), &udp_table, NULL);
 }

 INDIRECT_CALLABLE_SCOPE
 struct sk_buff *udp4_gro_receive(struct list_head *head, struct sk_buff *skb)
 {
 	struct udphdr *uh = udp_gro_udphdr(skb);
 	struct sock *sk = NULL;
 	struct sk_buff *pp;

 	if (unlikely(!uh))
 		goto flush;

 	/* Don't bother verifying checksum if we're going to flush anyway. */
 	if (NAPI_GRO_CB(skb)->flush)
 		goto skip;

 	if (skb_gro_checksum_validate_zero_check(skb, IPPROTO_UDP, uh->check,
 						 inet_gro_compute_pseudo))
 		goto flush;
 	else if (uh->check)
 		skb_gro_checksum_try_convert(skb, IPPROTO_UDP,
 					     inet_gro_compute_pseudo);
 skip:
 	NAPI_GRO_CB(skb)->is_ipv6 = 0;
 	rcu_read_lock();

 	if (static_branch_unlikely(&udp_encap_needed_key))
 		sk = udp4_gro_lookup_skb(skb, uh->source, uh->dest);

 	pp = udp_gro_receive(head, skb, uh, sk);
 	rcu_read_unlock();
 	return pp;

 flush:
 	NAPI_GRO_CB(skb)->flush = 1;
 	return NULL;
 }

 static int udp_gro_complete_segment(struct sk_buff *skb)
 {
 	struct udphdr *uh = udp_hdr(skb);

 	skb->csum_start = (unsigned char *)uh - skb->head;
 	skb->csum_offset = offsetof(struct udphdr, check);
 	skb->ip_summed = CHECKSUM_PARTIAL;

 	skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
 	skb_shinfo(skb)->gso_type |= SKB_GSO_UDP_L4;
 	return 0;
 }

 int udp_gro_complete(struct sk_buff *skb, int nhoff,
 		     udp_lookup_t lookup)
 {
 	__be16 newlen = htons(skb->len - nhoff);
 	struct udphdr *uh = (struct udphdr *)(skb->data + nhoff);
 	struct sock *sk;
 	int err;

 	uh->len = newlen;

 	rcu_read_lock();
 	sk = INDIRECT_CALL_INET(lookup, udp6_lib_lookup_skb,
 				udp4_lib_lookup_skb, skb, uh->source, uh->dest);
 	if (sk && udp_sk(sk)->gro_complete) {
 		skb_shinfo(skb)->gso_type = uh->check ? SKB_GSO_UDP_TUNNEL_CSUM
 					: SKB_GSO_UDP_TUNNEL;

 		/* clear the encap mark, so that inner frag_list gro_complete
 		 * can take place
 		 */
 		NAPI_GRO_CB(skb)->encap_mark = 0;

 		/* Set encapsulation before calling into inner gro_complete()
 		 * functions to make them set up the inner offsets.
 		 */
 		skb->encapsulation = 1;
 		err = udp_sk(sk)->gro_complete(sk, skb,
 				nhoff + sizeof(struct udphdr));
 	} else {
 		err = udp_gro_complete_segment(skb);
 	}
 	rcu_read_unlock();

 	if (skb->remcsum_offload)
 		skb_shinfo(skb)->gso_type |= SKB_GSO_TUNNEL_REMCSUM;

 	return err;
 }
 EXPORT_SYMBOL(udp_gro_complete);

 INDIRECT_CALLABLE_SCOPE int udp4_gro_complete(struct sk_buff *skb, int nhoff)
 {
 	const struct iphdr *iph = ip_hdr(skb);
 	struct udphdr *uh = (struct udphdr *)(skb->data + nhoff);

 	/* do fraglist only if there is no outer UDP encap (or we already processed it) */
 	if (NAPI_GRO_CB(skb)->is_flist && !NAPI_GRO_CB(skb)->encap_mark) {
 		uh->len = htons(skb->len - nhoff);

 		skb_shinfo(skb)->gso_type |= (SKB_GSO_FRAGLIST|SKB_GSO_UDP_L4);
 		skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;

 		if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
 			if (skb->csum_level < SKB_MAX_CSUM_LEVEL)
 				skb->csum_level++;
 		} else {
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
 			skb->csum_level = 0;
 		}

 		return 0;
 	}

 	if (uh->check)
 		uh->check = ~udp_v4_check(skb->len - nhoff, iph->saddr,
 					  iph->daddr, 0);

 	return udp_gro_complete(skb, nhoff, udp4_lib_lookup_skb);
 }

 static const struct net_offload udpv4_offload = {
 	.callbacks = {
 		.gso_segment = udp4_ufo_fragment,
 		.gro_receive  =	udp4_gro_receive,
 		.gro_complete =	udp4_gro_complete,
 	},
 };

 int __init udpv4_offload_init(void)
 {
 	return inet_add_offload(&udpv4_offload, IPPROTO_UDP);
 }
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* IPV4 GSO/GRO offload support
	* Linux INET implementation
	*
	* UDPv4 GSO support
	*/

	#include <linux/skbuff.h>
	#include <net/udp.h>
	#include <net/protocol.h>
	#include <net/inet_common.h>

	static struct sk_buff __skb_udp_tunnel_segment(struct sk_buff skb,
	netdev_features_t features,
	struct sk_buff (gso_inner_segment)(struct sk_buff *skb,
	netdev_features_t features),
	__be16 new_protocol, bool is_ipv6)
	{
	int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);
	bool remcsum, need_csum, offload_csum, gso_partial;
	struct sk_buff *segs = ERR_PTR(-EINVAL);
	struct udphdr *uh = udp_hdr(skb);
	u16 mac_offset = skb->mac_header;
	__be16 protocol = skb->protocol;
	u16 mac_len = skb->mac_len;
	int udp_offset, outer_hlen;
	__wsum partial;
	bool need_ipsec;

	if (unlikely(!pskb_may_pull(skb, tnl_hlen)))
	goto out;

	/* Adjust partial header checksum to negate old length.
	* We cannot rely on the value contained in uh->len as it is
	* possible that the actual value exceeds the boundaries of the
	* 16 bit length field due to the header being added outside of an
	* IP or IPv6 frame that was already limited to 64K - 1.
	*/
	if (skb_shinfo(skb)->gso_type & SKB_GSO_PARTIAL)
	partial = (__force __wsum)uh->len;
	else
	partial = (__force __wsum)htonl(skb->len);
	partial = csum_sub(csum_unfold(uh->check), partial);

	/* 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_set_transport_header(skb, skb_inner_transport_offset(skb));
	skb->mac_len = skb_inner_network_offset(skb);
	skb->protocol = new_protocol;

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

	remcsum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_TUNNEL_REMCSUM);
	skb->remcsum_offload = remcsum;

	need_ipsec = skb_dst(skb) && dst_xfrm(skb_dst(skb));
	/* Try to offload checksum if possible */
	offload_csum = !!(need_csum &&
	!need_ipsec &&
	(skb->dev->features &
	(is_ipv6 ? (NETIF_F_HW_CSUM \| NETIF_F_IPV6_CSUM) :
	(NETIF_F_HW_CSUM \| NETIF_F_IP_CSUM))));

	features &= skb->dev->hw_enc_features;
	if (need_csum)
	features &= ~NETIF_F_SCTP_CRC;

	/* The only checksum offload we care about from here on out is the
	* outer one so strip the existing checksum feature flags and
	* instead set the flag based on our outer checksum offload value.
	*/
	if (remcsum) {
	features &= ~NETIF_F_CSUM_MASK;
	if (!need_csum \|\| offload_csum)
	features \|= NETIF_F_HW_CSUM;
	}

	/* segment inner packet. */
	segs = gso_inner_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);
	udp_offset = outer_hlen - tnl_hlen;
	skb = segs;
	do {
	unsigned int len;

	if (remcsum)
	skb->ip_summed = CHECKSUM_NONE;

	/* 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, udp_offset);
	len = skb->len - udp_offset;
	uh = udp_hdr(skb);

	/* If we are only performing partial GSO the inner header
	* will be using a length value equal to only one MSS sized
	* segment instead of the entire frame.
	*/
	if (gso_partial && skb_is_gso(skb)) {
	uh->len = htons(skb_shinfo(skb)->gso_size +
	SKB_GSO_CB(skb)->data_offset +
	skb->head - (unsigned char *)uh);
	} else {
	uh->len = htons(len);
	}

	if (!need_csum)
	continue;

	uh->check = ~csum_fold(csum_add(partial,
	(__force __wsum)htonl(len)));

	if (skb->encapsulation \|\| !offload_csum) {
	uh->check = gso_make_checksum(skb, ~uh->check);
	if (uh->check == 0)
	uh->check = CSUM_MANGLED_0;
	} else {
	skb->ip_summed = CHECKSUM_PARTIAL;
	skb->csum_start = skb_transport_header(skb) - skb->head;
	skb->csum_offset = offsetof(struct udphdr, check);
	}
	} while ((skb = skb->next));
	out:
	return segs;
	}

	struct sk_buff skb_udp_tunnel_segment(struct sk_buff skb,
	netdev_features_t features,
	bool is_ipv6)
	{
	__be16 protocol = skb->protocol;
	const struct net_offload **offloads;
	const struct net_offload *ops;
	struct sk_buff *segs = ERR_PTR(-EINVAL);
	struct sk_buff (gso_inner_segment)(struct sk_buff *skb,
	netdev_features_t features);

	rcu_read_lock();

	switch (skb->inner_protocol_type) {
	case ENCAP_TYPE_ETHER:
	protocol = skb->inner_protocol;
	gso_inner_segment = skb_mac_gso_segment;
	break;
	case ENCAP_TYPE_IPPROTO:
	offloads = is_ipv6 ? inet6_offloads : inet_offloads;
	ops = rcu_dereference(offloads[skb->inner_ipproto]);
	if (!ops \|\| !ops->callbacks.gso_segment)
	goto out_unlock;
	gso_inner_segment = ops->callbacks.gso_segment;
	break;
	default:
	goto out_unlock;
	}

	segs = __skb_udp_tunnel_segment(skb, features, gso_inner_segment,
	protocol, is_ipv6);

	out_unlock:
	rcu_read_unlock();

	return segs;
	}
	EXPORT_SYMBOL(skb_udp_tunnel_segment);

	static void __udpv4_gso_segment_csum(struct sk_buff *seg,
	__be32 oldip, __be32 newip,
	__be16 oldport, __be16 newport)
	{
	struct udphdr *uh;
	struct iphdr *iph;

	if (oldip == newip && oldport == newport)
	return;

	uh = udp_hdr(seg);
	iph = ip_hdr(seg);

	if (uh->check) {
	inet_proto_csum_replace4(&uh->check, seg, oldip, newip,
	true);
	inet_proto_csum_replace2(&uh->check, seg, oldport, newport,
	false);
	if (!uh->check)
	uh->check = CSUM_MANGLED_0;
	}
	oldport = newport;

	csum_replace4(&iph->check, oldip, newip);
	oldip = newip;
	}

	static struct sk_buff __udpv4_gso_segment_list_csum(struct sk_buff segs)
	{
	struct sk_buff *seg;
	struct udphdr uh, uh2;
	struct iphdr iph, iph2;

	seg = segs;
	uh = udp_hdr(seg);
	iph = ip_hdr(seg);

	if ((udp_hdr(seg)->dest == udp_hdr(seg->next)->dest) &&
	(udp_hdr(seg)->source == udp_hdr(seg->next)->source) &&
	(ip_hdr(seg)->daddr == ip_hdr(seg->next)->daddr) &&
	(ip_hdr(seg)->saddr == ip_hdr(seg->next)->saddr))
	return segs;

	while ((seg = seg->next)) {
	uh2 = udp_hdr(seg);
	iph2 = ip_hdr(seg);

	__udpv4_gso_segment_csum(seg,
	&iph2->saddr, &iph->saddr,
	&uh2->source, &uh->source);
	__udpv4_gso_segment_csum(seg,
	&iph2->daddr, &iph->daddr,
	&uh2->dest, &uh->dest);
	}

	return segs;
	}

	static struct sk_buff __udp_gso_segment_list(struct sk_buff skb,
	netdev_features_t features,
	bool is_ipv6)
	{
	unsigned int mss = skb_shinfo(skb)->gso_size;

	skb = skb_segment_list(skb, features, skb_mac_header_len(skb));
	if (IS_ERR(skb))
	return skb;

	udp_hdr(skb)->len = htons(sizeof(struct udphdr) + mss);

	return is_ipv6 ? skb : __udpv4_gso_segment_list_csum(skb);
	}

	struct sk_buff __udp_gso_segment(struct sk_buff gso_skb,
	netdev_features_t features, bool is_ipv6)
	{
	struct sock *sk = gso_skb->sk;
	unsigned int sum_truesize = 0;
	struct sk_buff segs, seg;
	struct udphdr *uh;
	unsigned int mss;
	bool copy_dtor;
	__sum16 check;
	__be16 newlen;

	if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST)
	return __udp_gso_segment_list(gso_skb, features, is_ipv6);

	mss = skb_shinfo(gso_skb)->gso_size;
	if (gso_skb->len <= sizeof(*uh) + mss)
	return ERR_PTR(-EINVAL);

	skb_pull(gso_skb, sizeof(*uh));

	/* clear destructor to avoid skb_segment assigning it to tail */
	copy_dtor = gso_skb->destructor == sock_wfree;
	if (copy_dtor)
	gso_skb->destructor = NULL;

	segs = skb_segment(gso_skb, features);
	if (IS_ERR_OR_NULL(segs)) {
	if (copy_dtor)
	gso_skb->destructor = sock_wfree;
	return segs;
	}

	/* GSO partial and frag_list segmentation only requires splitting
	* the frame into an MSS multiple and possibly a remainder, both
	* cases return a GSO skb. So update the mss now.
	*/
	if (skb_is_gso(segs))
	mss *= skb_shinfo(segs)->gso_segs;

	seg = segs;
	uh = udp_hdr(seg);

	/* preserve TX timestamp flags and TS key for first segment */
	skb_shinfo(seg)->tskey = skb_shinfo(gso_skb)->tskey;
	skb_shinfo(seg)->tx_flags \|=
	(skb_shinfo(gso_skb)->tx_flags & SKBTX_ANY_TSTAMP);

	/* compute checksum adjustment based on old length versus new */
	newlen = htons(sizeof(*uh) + mss);
	check = csum16_add(csum16_sub(uh->check, uh->len), newlen);

	for (;;) {
	if (copy_dtor) {
	seg->destructor = sock_wfree;
	seg->sk = sk;
	sum_truesize += seg->truesize;
	}

	if (!seg->next)
	break;

	uh->len = newlen;
	uh->check = check;

	if (seg->ip_summed == CHECKSUM_PARTIAL)
	gso_reset_checksum(seg, ~check);
	else
	uh->check = gso_make_checksum(seg, ~check) ? :
	CSUM_MANGLED_0;

	seg = seg->next;
	uh = udp_hdr(seg);
	}

	/* last packet can be partial gso_size, account for that in checksum */
	newlen = htons(skb_tail_pointer(seg) - skb_transport_header(seg) +
	seg->data_len);
	check = csum16_add(csum16_sub(uh->check, uh->len), newlen);

	uh->len = newlen;
	uh->check = check;

	if (seg->ip_summed == CHECKSUM_PARTIAL)
	gso_reset_checksum(seg, ~check);
	else
	uh->check = gso_make_checksum(seg, ~check) ? : CSUM_MANGLED_0;

	/* update refcount for the packet */
	if (copy_dtor) {
	int delta = sum_truesize - gso_skb->truesize;

	/* In some pathological cases, delta can be negative.
	* We need to either use refcount_add() or refcount_sub_and_test()
	*/
	if (likely(delta >= 0))
	refcount_add(delta, &sk->sk_wmem_alloc);
	else
	WARN_ON_ONCE(refcount_sub_and_test(-delta, &sk->sk_wmem_alloc));
	}
	return segs;
	}
	EXPORT_SYMBOL_GPL(__udp_gso_segment);

	static struct sk_buff udp4_ufo_fragment(struct sk_buff skb,
	netdev_features_t features)
	{
	struct sk_buff *segs = ERR_PTR(-EINVAL);
	unsigned int mss;
	__wsum csum;
	struct udphdr *uh;
	struct iphdr *iph;

	if (skb->encapsulation &&
	(skb_shinfo(skb)->gso_type &
	(SKB_GSO_UDP_TUNNEL\|SKB_GSO_UDP_TUNNEL_CSUM))) {
	segs = skb_udp_tunnel_segment(skb, features, false);
	goto out;
	}

	if (!(skb_shinfo(skb)->gso_type & (SKB_GSO_UDP \| SKB_GSO_UDP_L4)))
	goto out;

	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
	goto out;

	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
	return __udp_gso_segment(skb, features, false);

	mss = skb_shinfo(skb)->gso_size;
	if (unlikely(skb->len <= mss))
	goto out;

	/* Do software UFO. Complete and fill in the UDP checksum as
	* HW cannot do checksum of UDP packets sent as multiple
	* IP fragments.
	*/

	uh = udp_hdr(skb);
	iph = ip_hdr(skb);

	uh->check = 0;
	csum = skb_checksum(skb, 0, skb->len, 0);
	uh->check = udp_v4_check(skb->len, iph->saddr, iph->daddr, csum);
	if (uh->check == 0)
	uh->check = CSUM_MANGLED_0;

	skb->ip_summed = CHECKSUM_UNNECESSARY;

	/* If there is no outer header we can fake a checksum offload
	* due to the fact that we have already done the checksum in
	* software prior to segmenting the frame.
	*/
	if (!skb->encap_hdr_csum)
	features \|= NETIF_F_HW_CSUM;

	/* Fragment the skb. IP headers of the fragments are updated in
	* inet_gso_segment()
	*/
	segs = skb_segment(skb, features);
	out:
	return segs;
	}

	#define UDP_GRO_CNT_MAX 64
	static struct sk_buff udp_gro_receive_segment(struct list_head head,
	struct sk_buff *skb)
	{
	struct udphdr *uh = udp_gro_udphdr(skb);
	struct sk_buff *pp = NULL;
	struct udphdr *uh2;
	struct sk_buff *p;
	unsigned int ulen;
	int ret = 0;

	/* requires non zero csum, for symmetry with GSO */
	if (!uh->check) {
	NAPI_GRO_CB(skb)->flush = 1;
	return NULL;
	}

	/* Do not deal with padded or malicious packets, sorry ! */
	ulen = ntohs(uh->len);
	if (ulen <= sizeof(*uh) \|\| ulen != skb_gro_len(skb)) {
	NAPI_GRO_CB(skb)->flush = 1;
	return NULL;
	}
	/* pull encapsulating udp header */
	skb_gro_pull(skb, sizeof(struct udphdr));

	list_for_each_entry(p, head, list) {
	if (!NAPI_GRO_CB(p)->same_flow)
	continue;

	uh2 = udp_hdr(p);

	/* Match ports only, as csum is always non zero */
	if (((u32 )&uh->source != (u32 )&uh2->source)) {
	NAPI_GRO_CB(p)->same_flow = 0;
	continue;
	}

	if (NAPI_GRO_CB(skb)->is_flist != NAPI_GRO_CB(p)->is_flist) {
	NAPI_GRO_CB(skb)->flush = 1;
	return p;
	}

	/* Terminate the flow on len mismatch or if it grow "too much".
	* Under small packet flood GRO count could elsewhere grow a lot
	* leading to excessive truesize values.
	* On len mismatch merge the first packet shorter than gso_size,
	* otherwise complete the GRO packet.
	*/
	if (ulen > ntohs(uh2->len)) {
	pp = p;
	} else {
	if (NAPI_GRO_CB(skb)->is_flist) {
	if (!pskb_may_pull(skb, skb_gro_offset(skb))) {
	NAPI_GRO_CB(skb)->flush = 1;
	return NULL;
	}
	if ((skb->ip_summed != p->ip_summed) \|\|
	(skb->csum_level != p->csum_level)) {
	NAPI_GRO_CB(skb)->flush = 1;
	return NULL;
	}
	ret = skb_gro_receive_list(p, skb);
	} else {
	skb_gro_postpull_rcsum(skb, uh,
	sizeof(struct udphdr));

	ret = skb_gro_receive(p, skb);
	}
	}

	if (ret \|\| ulen != ntohs(uh2->len) \|\|
	NAPI_GRO_CB(p)->count >= UDP_GRO_CNT_MAX)
	pp = p;

	return pp;
	}

	/* mismatch, but we never need to flush */
	return NULL;
	}

	struct sk_buff udp_gro_receive(struct list_head head, struct sk_buff *skb,
	struct udphdr uh, struct sock sk)
	{
	struct sk_buff *pp = NULL;
	struct sk_buff *p;
	struct udphdr *uh2;
	unsigned int off = skb_gro_offset(skb);
	int flush = 1;

	/* we can do L4 aggregation only if the packet can't land in a tunnel
	* otherwise we could corrupt the inner stream
	*/
	NAPI_GRO_CB(skb)->is_flist = 0;
	if (!sk \|\| !udp_sk(sk)->gro_receive) {
	if (skb->dev->features & NETIF_F_GRO_FRAGLIST)
	NAPI_GRO_CB(skb)->is_flist = sk ? !udp_sk(sk)->gro_enabled : 1;

	if ((!sk && (skb->dev->features & NETIF_F_GRO_UDP_FWD)) \|\|
	(sk && udp_sk(sk)->gro_enabled) \|\| NAPI_GRO_CB(skb)->is_flist)
	pp = call_gro_receive(udp_gro_receive_segment, head, skb);
	return pp;
	}

	if (NAPI_GRO_CB(skb)->encap_mark \|\|
	(uh->check && skb->ip_summed != CHECKSUM_PARTIAL &&
	NAPI_GRO_CB(skb)->csum_cnt == 0 &&
	!NAPI_GRO_CB(skb)->csum_valid))
	goto out;

	/* mark that this skb passed once through the tunnel gro layer */
	NAPI_GRO_CB(skb)->encap_mark = 1;

	flush = 0;

	list_for_each_entry(p, head, list) {
	if (!NAPI_GRO_CB(p)->same_flow)
	continue;

	uh2 = (struct udphdr *)(p->data + off);

	/* Match ports and either checksums are either both zero
	* or nonzero.
	*/
	if (((u32 )&uh->source != (u32 )&uh2->source) \|\|
	(!uh->check ^ !uh2->check)) {
	NAPI_GRO_CB(p)->same_flow = 0;
	continue;
	}
	}

	skb_gro_pull(skb, sizeof(struct udphdr)); /* pull encapsulating udp header */
	skb_gro_postpull_rcsum(skb, uh, sizeof(struct udphdr));
	pp = call_gro_receive_sk(udp_sk(sk)->gro_receive, sk, head, skb);

	out:
	skb_gro_flush_final(skb, pp, flush);
	return pp;
	}
	EXPORT_SYMBOL(udp_gro_receive);

	static struct sock udp4_gro_lookup_skb(struct sk_buff skb, __be16 sport,
	__be16 dport)
	{
	const struct iphdr *iph = skb_gro_network_header(skb);

	return __udp4_lib_lookup(dev_net(skb->dev), iph->saddr, sport,
	iph->daddr, dport, inet_iif(skb),
	inet_sdif(skb), &udp_table, NULL);
	}

	INDIRECT_CALLABLE_SCOPE
	struct sk_buff udp4_gro_receive(struct list_head head, struct sk_buff *skb)
	{
	struct udphdr *uh = udp_gro_udphdr(skb);
	struct sock *sk = NULL;
	struct sk_buff *pp;

	if (unlikely(!uh))
	goto flush;

	/* Don't bother verifying checksum if we're going to flush anyway. */
	if (NAPI_GRO_CB(skb)->flush)
	goto skip;

	if (skb_gro_checksum_validate_zero_check(skb, IPPROTO_UDP, uh->check,
	inet_gro_compute_pseudo))
	goto flush;
	else if (uh->check)
	skb_gro_checksum_try_convert(skb, IPPROTO_UDP,
	inet_gro_compute_pseudo);
	skip:
	NAPI_GRO_CB(skb)->is_ipv6 = 0;
	rcu_read_lock();

	if (static_branch_unlikely(&udp_encap_needed_key))
	sk = udp4_gro_lookup_skb(skb, uh->source, uh->dest);

	pp = udp_gro_receive(head, skb, uh, sk);
	rcu_read_unlock();
	return pp;

	flush:
	NAPI_GRO_CB(skb)->flush = 1;
	return NULL;
	}

	static int udp_gro_complete_segment(struct sk_buff *skb)
	{
	struct udphdr *uh = udp_hdr(skb);

	skb->csum_start = (unsigned char *)uh - skb->head;
	skb->csum_offset = offsetof(struct udphdr, check);
	skb->ip_summed = CHECKSUM_PARTIAL;

	skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
	skb_shinfo(skb)->gso_type \|= SKB_GSO_UDP_L4;
	return 0;
	}

	int udp_gro_complete(struct sk_buff *skb, int nhoff,
	udp_lookup_t lookup)
	{
	__be16 newlen = htons(skb->len - nhoff);
	struct udphdr uh = (struct udphdr )(skb->data + nhoff);
	struct sock *sk;
	int err;

	uh->len = newlen;

	rcu_read_lock();
	sk = INDIRECT_CALL_INET(lookup, udp6_lib_lookup_skb,
	udp4_lib_lookup_skb, skb, uh->source, uh->dest);
	if (sk && udp_sk(sk)->gro_complete) {
	skb_shinfo(skb)->gso_type = uh->check ? SKB_GSO_UDP_TUNNEL_CSUM
	: SKB_GSO_UDP_TUNNEL;

	/* clear the encap mark, so that inner frag_list gro_complete
	* can take place
	*/
	NAPI_GRO_CB(skb)->encap_mark = 0;

	/* Set encapsulation before calling into inner gro_complete()
	* functions to make them set up the inner offsets.
	*/
	skb->encapsulation = 1;
	err = udp_sk(sk)->gro_complete(sk, skb,
	nhoff + sizeof(struct udphdr));
	} else {
	err = udp_gro_complete_segment(skb);
	}
	rcu_read_unlock();

	if (skb->remcsum_offload)
	skb_shinfo(skb)->gso_type \|= SKB_GSO_TUNNEL_REMCSUM;

	return err;
	}
	EXPORT_SYMBOL(udp_gro_complete);

	INDIRECT_CALLABLE_SCOPE int udp4_gro_complete(struct sk_buff *skb, int nhoff)
	{
	const struct iphdr *iph = ip_hdr(skb);
	struct udphdr uh = (struct udphdr )(skb->data + nhoff);

	/* do fraglist only if there is no outer UDP encap (or we already processed it) */
	if (NAPI_GRO_CB(skb)->is_flist && !NAPI_GRO_CB(skb)->encap_mark) {
	uh->len = htons(skb->len - nhoff);

	skb_shinfo(skb)->gso_type \|= (SKB_GSO_FRAGLIST\|SKB_GSO_UDP_L4);
	skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;

	if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
	if (skb->csum_level < SKB_MAX_CSUM_LEVEL)
	skb->csum_level++;
	} else {
	skb->ip_summed = CHECKSUM_UNNECESSARY;
	skb->csum_level = 0;
	}

	return 0;
	}

	if (uh->check)
	uh->check = ~udp_v4_check(skb->len - nhoff, iph->saddr,
	iph->daddr, 0);

	return udp_gro_complete(skb, nhoff, udp4_lib_lookup_skb);
	}

	static const struct net_offload udpv4_offload = {
	.callbacks = {
	.gso_segment = udp4_ufo_fragment,
	.gro_receive = udp4_gro_receive,
	.gro_complete = udp4_gro_complete,
	},
	};

	int __init udpv4_offload_init(void)
	{
	return inet_add_offload(&udpv4_offload, IPPROTO_UDP);
	}