udp:nat:vxlan tx after nat should recsum if vxlan tx offload on

    If vxlan-dev enable tx csum offload, there are two case of CHECKSUM_PARTIAL,
    but udp->check donot have the both meanings.

    1. vxlan-dev disable tx csum offload, udp->check is just pseudo hdr.
    2. vxlan-dev enable tx csum offload, udp->check is pseudo hdr and
       csum from outter l4 to innner l4.

    Unfortunately if there is a nat process after vxlan tx，udp_manip_pkt just use
    CSUM_PARTIAL to re csum PKT, which is just right on vxlan tx csum disable offload.

    This patch use skb->csum_local flag to identify two case, which will csum lco_csum if valid.

Signed-off-by: chenwei.0515 <chenwei.0515@bytedance.com>

include/linux/skbuff.h

@@ -990,6 +990,7 @@ struct sk_buff {
 	__u8			slow_gro:1;
 	__u8			csum_not_inet:1;
 	__u8			scm_io_uring:1;
+	__u8			csum_local:1;
 
 #ifdef CONFIG_NET_SCHED
 	__u16			tc_index;	/* traffic control index */

net/ipv4/udp.c

@@ -889,6 +889,7 @@ void udp_set_csum(bool nocheck, struct sk_buff *skb,
 		uh->check = udp_v4_check(len, saddr, daddr, lco_csum(skb));
 		if (uh->check == 0)
 			uh->check = CSUM_MANGLED_0;
+		skb->csum_local = 1;
 	} else {
 		skb->ip_summed = CHECKSUM_PARTIAL;
 		skb->csum_start = skb_transport_header(skb) - skb->head;

net/netfilter/nf_nat_proto.c

@@ -25,6 +25,7 @@
 #include <net/ip6_route.h>
 #include <net/xfrm.h>
 #include <net/ipv6.h>
+#include <net/udp.h>
 
 #include <net/netfilter/nf_conntrack_core.h>
 #include <net/netfilter/nf_conntrack.h>
@@ -75,6 +76,14 @@ static bool udp_manip_pkt(struct sk_buff *skb,
 	hdr = (struct udphdr *)(skb->data + hdroff);
 	__udp_manip_pkt(skb, iphdroff, hdr, tuple, maniptype, !!hdr->check);
 
+	if (skb->csum_local) {
+		hdr->check = 0;
+		hdr->check = udp_v4_check(htons(hdr->len), tuple->src.u3.ip, tuple->dst.u3.ip,
+					  lco_csum(skb));
+		if (hdr->check == 0)
+			hdr->check = CSUM_MANGLED_0;
+	}
+
 	return true;
 }