ipvs: use parsed transport offset in TCP state lookup

TCP state handling reparses the skb to find the TCP header. For IPv6 it
uses sizeof(struct ipv6hdr), while the surrounding IPVS code already
parsed the packet with ip_vs_fill_iph_skb() and has the real
transport-header offset in iph.len.

This makes TCP state handling look at the wrong bytes when an IPv6
packet carries extension headers. Use the parsed transport offset passed
down from ip_vs_set_state() when reading the TCP header.

For IPv4 and for IPv6 packets without extension headers, the passed
offset matches the previous value.

Fixes: 0bbdd42b7efa6 ("IPVS: Extend protocol DNAT/SNAT and state handlers")
Link: https://lore.kernel.org/netdev/20260705125659.37744-1-zhaoyz24@mails.tsinghua.edu.cn/
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Assisted-by: Claude Code:GLM-5.2
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 1 insertions, 7 deletions

diff --git a/net/netfilter/ipvs/ip_vs_proto_tcp.c b/net/netfilter/ipvs/ip_vs_proto_tcp.c
index 2d3f6aeafe52..f86b763efcc4 100644
--- a/net/netfilter/ipvs/ip_vs_proto_tcp.c
+++ b/net/netfilter/ipvs/ip_vs_proto_tcp.c
@@ -584,13 +584,7 @@ tcp_state_transition(struct ip_vs_conn *cp, int direction,
 {
 	struct tcphdr _tcph, *th;
 
-#ifdef CONFIG_IP_VS_IPV6
-	int ihl = cp->af == AF_INET ? ip_hdrlen(skb) : sizeof(struct ipv6hdr);
-#else
-	int ihl = ip_hdrlen(skb);
-#endif
-
-	th = skb_header_pointer(skb, ihl, sizeof(_tcph), &_tcph);
+	th = skb_header_pointer(skb, iph_len, sizeof(_tcph), &_tcph);
 	if (th == NULL)
 		return;