We should disallow normal connections with cport 0 to be
created from packets by the scheduler (from clients) or
by ip_vs_new_conn_out (from real servers) because later
such traffic can not hit the connection due to the
NO_CPORT requirement. As result, it can lead to duplicate
connection for every packet. Do the same for vport 0.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260925141115.16126-1-axel.mierczuk%401password.com
Signed-off-by: Julian Anastasov <ja@ssi.bg>
---
 net/netfilter/ipvs/ip_vs_core.c       | 3 ++-
 net/netfilter/ipvs/ip_vs_proto_sctp.c | 5 +++++
 net/netfilter/ipvs/ip_vs_proto_tcp.c  | 5 +++++
 net/netfilter/ipvs/ip_vs_proto_udp.c  | 4 ++++
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index 397d5392ebed..8cdcab7d6edf 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -1306,6 +1306,7 @@ static inline bool is_new_conn_expected(const struct ip_vs_conn *cp,
  *    In fwmark-VS actual vaddr and vport are unknown to IPVS
  * 2) Real Server and Virtual Service were NOT configured without port:
  *    This is to allow match of different VS to the same RS ip-addr
+ * 3) Client port is not 0
  */
 struct ip_vs_conn *ip_vs_new_conn_out(struct ip_vs_service *svc,
 				      struct ip_vs_dest *dest,
@@ -1329,7 +1330,7 @@ struct ip_vs_conn *ip_vs_new_conn_out(struct ip_vs_service *svc,
 	/* check pre-requisites are satisfied */
 	if (svc->fwmark)
 		return NULL;
-	if (!vport || !dport)
+	if (!vport || !dport || !cport)
 		return NULL;
 
 	/* for persistent service first create connection template */
diff --git a/net/netfilter/ipvs/ip_vs_proto_sctp.c b/net/netfilter/ipvs/ip_vs_proto_sctp.c
index fb8af6b15a39..83d1443ebe01 100644
--- a/net/netfilter/ipvs/ip_vs_proto_sctp.c
+++ b/net/netfilter/ipvs/ip_vs_proto_sctp.c
@@ -30,6 +30,7 @@ sctp_conn_schedule(struct netns_ipvs *ipvs, int af, struct sk_buff *skb,
 			sch = skb_header_pointer(skb, iph->len + sizeof(_sctph),
 						 sizeof(_schunkh), &_schunkh);
 			if (sch) {
+				/* Accept packet without scheduling? */
 				if (sch->type == SCTP_CID_ABORT ||
 				    !(sysctl_sloppy_sctp(ipvs) ||
 				      sch->type == SCTP_CID_INIT))
@@ -47,6 +48,10 @@ sctp_conn_schedule(struct netns_ipvs *ipvs, int af, struct sk_buff *skb,
 		return 0;
 	}
 
+	/* Do not create connection for port 0, skip the packet */
+	if (!ports[0] || !ports[1])
+		return 1;
+
 	if (likely(!ip_vs_iph_inverse(iph)))
 		svc = ip_vs_service_find(ipvs, af, skb->mark, iph->protocol,
 					 &iph->daddr, ports[1]);
diff --git a/net/netfilter/ipvs/ip_vs_proto_tcp.c b/net/netfilter/ipvs/ip_vs_proto_tcp.c
index fec0e8b47b71..2e55b62445c6 100644
--- a/net/netfilter/ipvs/ip_vs_proto_tcp.c
+++ b/net/netfilter/ipvs/ip_vs_proto_tcp.c
@@ -48,6 +48,7 @@ tcp_conn_schedule(struct netns_ipvs *ipvs, int af, struct sk_buff *skb,
 	if (likely(!ip_vs_iph_icmp(iph))) {
 		th = skb_header_pointer(skb, iph->len, sizeof(_tcph), &_tcph);
 		if (th) {
+			/* Accept packet without scheduling? */
 			if (th->rst || !(sysctl_sloppy_tcp(ipvs) || th->syn))
 				return 1;
 			ports = &th->source;
@@ -62,6 +63,10 @@ tcp_conn_schedule(struct netns_ipvs *ipvs, int af, struct sk_buff *skb,
 		return 0;
 	}
 
+	/* Do not create connection for port 0, skip the packet */
+	if (!ports[0] || !ports[1])
+		return 1;
+
 	/* No !th->ack check to allow scheduling on SYN+ACK for Active FTP */
 
 	if (likely(!ip_vs_iph_inverse(iph)))
diff --git a/net/netfilter/ipvs/ip_vs_proto_udp.c b/net/netfilter/ipvs/ip_vs_proto_udp.c
index f32785682402..92c0b76c1a02 100644
--- a/net/netfilter/ipvs/ip_vs_proto_udp.c
+++ b/net/netfilter/ipvs/ip_vs_proto_udp.c
@@ -52,6 +52,10 @@ udp_conn_schedule(struct netns_ipvs *ipvs, int af, struct sk_buff *skb,
 		return 0;
 	}
 
+	/* Do not create connection for port 0, skip the packet */
+	if (!ports[0] || !ports[1])
+		return 1;
+
 	if (likely(!ip_vs_iph_inverse(iph)))
 		svc = ip_vs_service_find(ipvs, af, skb->mark, iph->protocol,
 					 &iph->daddr, ports[1]);
-- 
2.55.0