kernel: fix IPv6 TCP GSO segmentation with NAT

Add missing checksum update

Fixes: https://github.com/openwrt/openwrt/issues/15857
Signed-off-by: Felix Fietkau <nbd@nbd.name>

diff --git a/target/linux/generic/pending-6.6/686-net-ipv6-fix-TCP-GSO-segmentation-with-NAT.patch b/target/linux/generic/pending-6.6/686-net-ipv6-fix-TCP-GSO-segmentation-with-NAT.patch
new file mode 100644 (file)
index 0000000..9591e16
--- /dev/null
+++ b/target/linux/generic/pending-6.6/686-net-ipv6-fix-TCP-GSO-segmentation-with-NAT.patch
@@ -0,0 +1,54 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Mon, 24 Feb 2025 12:18:23 +0100
+Subject: [PATCH] net: ipv6: fix TCP GSO segmentation with NAT
+
+When updating the source/destination address, the TCP/UDP checksum needs to
+be updated as well.
+
+Fixes: bee88cd5bd83 ("net: add support for segmenting TCP fraglist GSO packets")
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/ipv6/tcpv6_offload.c
++++ b/net/ipv6/tcpv6_offload.c
+@@ -112,24 +112,36 @@ static struct sk_buff *__tcpv6_gso_segme
+       struct sk_buff *seg;
+       struct tcphdr *th2;
+       struct ipv6hdr *iph2;
++      bool addr_equal;
+ 
+       seg = segs;
+       th = tcp_hdr(seg);
+       iph = ipv6_hdr(seg);
+       th2 = tcp_hdr(seg->next);
+       iph2 = ipv6_hdr(seg->next);
++      addr_equal = ipv6_addr_equal(&iph->saddr, &iph2->saddr) &&
++                   ipv6_addr_equal(&iph->daddr, &iph2->daddr);
+ 
+       if (!(*(const u32 *)&th->source ^ *(const u32 *)&th2->source) &&
+-          ipv6_addr_equal(&iph->saddr, &iph2->saddr) &&
+-          ipv6_addr_equal(&iph->daddr, &iph2->daddr))
++          addr_equal)
+               return segs;
+ 
+       while ((seg = seg->next)) {
+               th2 = tcp_hdr(seg);
+               iph2 = ipv6_hdr(seg);
+ 
+-              iph2->saddr = iph->saddr;
+-              iph2->daddr = iph->daddr;
++              if (!addr_equal) {
++                      inet_proto_csum_replace16(&th2->check, seg,
++                                                iph2->saddr.s6_addr32,
++                                                iph->saddr.s6_addr32,
++                                                true);
++                      inet_proto_csum_replace16(&th2->check, seg,
++                                                iph2->daddr.s6_addr32,
++                                                iph->daddr.s6_addr32,
++                                                true);
++                      iph2->saddr = iph->saddr;
++                      iph2->daddr = iph->daddr;
++              }
+               __tcpv6_gso_segment_csum(seg, &th2->source, th->source);
+               __tcpv6_gso_segment_csum(seg, &th2->dest, th->dest);
+       }