Subject: [PATCH net 07/10] ipvs: skip ipv6 extension headers for csum checks

From: Florian Westphal <[email-masked]>
Date: Tue, 17 Feb 2026 17:32:30 +0100

From: Julian Anastasov <[email-masked]>

Protocol checksum validation fails for IPv6 if there are extension
headers before the protocol header. iph->len already contains its
offset, so use it to fix the problem.

Fixes: 2906f66a5682 ("ipvs: SCTP Trasport Loadbalancing Support")
Fixes: 0bbdd42b7efa ("IPVS: Extend protocol DNAT/SNAT and state handlers")
Signed-off-by: Julian Anastasov <[email-masked]>
Signed-off-by: Florian Westphal <[email-masked]>
---
 net/netfilter/ipvs/ip_vs_proto_sctp.c | 18 ++++++------------
 net/netfilter/ipvs/ip_vs_proto_tcp.c  | 21 +++++++--------------
 net/netfilter/ipvs/ip_vs_proto_udp.c  | 20 +++++++-------------
 3 files changed, 20 insertions(+), 39 deletions(-)

diff --git a/net/netfilter/ipvs/ip_vs_proto_sctp.c b/net/netfilter/ipvs/ip_vs_proto_sctp.c
index 83e452916403..63c78a1f3918 100644
--- a/net/netfilter/ipvs/ip_vs_proto_sctp.c
+++ b/net/netfilter/ipvs/ip_vs_proto_sctp.c
@@ -10,7 +10,8 @@
 #include <net/ip_vs.h>
 
 static int
-sctp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp);
+sctp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp,
+		unsigned int sctphoff);
 
 static int
 sctp_conn_schedule(struct netns_ipvs *ipvs, int af, struct sk_buff *skb,
@@ -108,7 +109,7 @@ sctp_snat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
 		int ret;
 
 		/* Some checks before mangling */
-		if (!sctp_csum_check(cp->af, skb, pp))
+		if (!sctp_csum_check(cp->af, skb, pp, sctphoff))
 			return 0;
 
 		/* Call application helper if needed */
@@ -156,7 +157,7 @@ sctp_dnat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
 		int ret;
 
 		/* Some checks before mangling */
-		if (!sctp_csum_check(cp->af, skb, pp))
+		if (!sctp_csum_check(cp->af, skb, pp, sctphoff))
 			return 0;
 
 		/* Call application helper if needed */
@@ -185,19 +186,12 @@ sctp_dnat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
 }
 
 static int
-sctp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp)
+sctp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp,
+		unsigned int sctphoff)
 {
-	unsigned int sctphoff;
 	struct sctphdr *sh;
 	__le32 cmp, val;
 
-#ifdef CONFIG_IP_VS_IPV6
-	if (af == AF_INET6)
-		sctphoff = sizeof(struct ipv6hdr);
-	else
-#endif
-		sctphoff = ip_hdrlen(skb);
-
 	sh = (struct sctphdr *)(skb->data + sctphoff);
 	cmp = sh->checksum;
 	val = sctp_compute_cksum(skb, sctphoff);
diff --git a/net/netfilter/ipvs/ip_vs_proto_tcp.c b/net/netfilter/ipvs/ip_vs_proto_tcp.c
index f68a1533ee45..8cc0a8ce6241 100644
--- a/net/netfilter/ipvs/ip_vs_proto_tcp.c
+++ b/net/netfilter/ipvs/ip_vs_proto_tcp.c
@@ -28,7 +28,8 @@
 #include <net/ip_vs.h>
 
 static int
-tcp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp);
+tcp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp,
+	       unsigned int tcphoff);
 
 static int
 tcp_conn_schedule(struct netns_ipvs *ipvs, int af, struct sk_buff *skb,
@@ -165,7 +166,7 @@ tcp_snat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
 		int ret;
 
 		/* Some checks before mangling */
-		if (!tcp_csum_check(cp->af, skb, pp))
+		if (!tcp_csum_check(cp->af, skb, pp, tcphoff))
 			return 0;
 
 		/* Call application helper if needed */
@@ -243,7 +244,7 @@ tcp_dnat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
 		int ret;
 
 		/* Some checks before mangling */
-		if (!tcp_csum_check(cp->af, skb, pp))
+		if (!tcp_csum_check(cp->af, skb, pp, tcphoff))
 			return 0;
 
 		/*
@@ -300,17 +301,9 @@ tcp_dnat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,

 static int
-tcp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp)
+tcp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp,
+	       unsigned int tcphoff)
 {
-	unsigned int tcphoff;
-
-#ifdef CONFIG_IP_VS_IPV6
-	if (af == AF_INET6)
-		tcphoff = sizeof(struct ipv6hdr);
-	else
-#endif
-		tcphoff = ip_hdrlen(skb);
-
 	switch (skb->ip_summed) {
 	case CHECKSUM_NONE:
 		skb->csum = skb_checksum(skb, tcphoff, skb->len - tcphoff, 0);
@@ -321,7 +314,7 @@ tcp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp)
 			if (csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
 					    &ipv6_hdr(skb)->daddr,
 					    skb->len - tcphoff,
-					    ipv6_hdr(skb)->nexthdr,
+					    IPPROTO_TCP,
 					    skb->csum)) {
 				IP_VS_DBG_RL_PKT(0, af, pp, skb, 0,
 						 "Failed checksum for");
diff --git a/net/netfilter/ipvs/ip_vs_proto_udp.c b/net/netfilter/ipvs/ip_vs_proto_udp.c
index 0f0107c80dd2..f9de632e38cd 100644
--- a/net/netfilter/ipvs/ip_vs_proto_udp.c
+++ b/net/netfilter/ipvs/ip_vs_proto_udp.c
@@ -24,7 +24,8 @@
 #include <net/ip6_checksum.h>
 
 static int
-udp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp);
+udp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp,
+	       unsigned int udphoff);
 
 static int
 udp_conn_schedule(struct netns_ipvs *ipvs, int af, struct sk_buff *skb,
@@ -154,7 +155,7 @@ udp_snat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
 		int ret;
 
 		/* Some checks before mangling */
-		if (!udp_csum_check(cp->af, skb, pp))
+		if (!udp_csum_check(cp->af, skb, pp, udphoff))
 			return 0;
 
 		/*
@@ -237,7 +238,7 @@ udp_dnat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
 		int ret;
 
 		/* Some checks before mangling */
-		if (!udp_csum_check(cp->af, skb, pp))
+		if (!udp_csum_check(cp->af, skb, pp, udphoff))
 			return 0;
 
 		/*
@@ -296,17 +297,10 @@ udp_dnat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,

 static int
-udp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp)
+udp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp,
+	       unsigned int udphoff)
 {
 	struct udphdr _udph, *uh;
-	unsigned int udphoff;
-
-#ifdef CONFIG_IP_VS_IPV6
-	if (af == AF_INET6)
-		udphoff = sizeof(struct ipv6hdr);
-	else
-#endif
-		udphoff = ip_hdrlen(skb);
 
 	uh = skb_header_pointer(skb, udphoff, sizeof(_udph), &_udph);
 	if (uh == NULL)
@@ -324,7 +318,7 @@ udp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp)
 				if (csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
 						    &ipv6_hdr(skb)->daddr,
 						    skb->len - udphoff,
-						    ipv6_hdr(skb)->nexthdr,
+						    IPPROTO_UDP,
 						    skb->csum)) {
 					IP_VS_DBG_RL_PKT(0, af, pp, skb, 0,
 							 "Failed checksum for");
-- 
2.52.0