ipvs: handle connections started by real-servers

When using LVS-NAT and SIP persistence-egine over UDP, the following
limitations are present with current implementation:

  1) To actually have load-balancing based on Call-ID header, you need to
     use one-packet-scheduling mode. But with one-packet-scheduling the
     connection is deleted just after packet is forwarded, so SIP responses
     coming from real-servers do not match any connection and SNAT is
     not applied.

  2) If you do not use "-o" option, IPVS behaves as normal UDP load
     balancer, so different SIP calls (each one identified by a different
     Call-ID) coming from the same ip-address/port go to the same
     real-server. So basically you don’t have load-balancing based on
     Call-ID as intended.

  3) Call-ID is not learned when a new SIP call is started by a real-server
     (inside-to-outside direction), but only in the outside-to-inside
     direction. This would be a general problem for all SIP servers acting
     as Back2BackUserAgent.

This patch aims to solve problems 1) and 3) while keeping OPS mode
mandatory for SIP-UDP, so that 2) is not a problem anymore.

The basic mechanism implemented is to make packets, that do not match any
existent connection but come from real-servers, create new connections
instead of let them pass without any effect.
When such packets pass through ip_vs_out(), if their source ip address and
source port match a configured real-server, a new connection is
automatically created in the same way as it would have happened if the
packet had come from outside-to-inside direction. A new connection template
is created too if the virtual-service is persistent and there is no
matching connection template found. The new connection automatically
created, if the service had "-o" option, is an OPS connection that lasts
only the time to forward the packet, just like it happens on the
ingress side.

The main part of this mechanism is implemented inside a persistent-engine
specific callback (at the moment only SIP persistent engine exists) and
is triggered only for UDP packets, since connection oriented protocols, by
using different set of ports (typically ephemeral ports) to open new
outgoing connections, should not need this feature.

The following requisites are needed for automatic connection creation; if
any is missing the packet simply goes the same way as before.
a) virtual-service is not fwmark based (this is because fwmark services
   do not store address and port of the virtual-service, required to
   build the connection data).
b) virtual-service and real-servers must not have been configured with
   omitted port (this is again to have all data to create the connection).

Signed-off-by: Marco Angaroni <marcoangaroni@gmail.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>

include/net/ip_vs.h

@@ -731,6 +731,12 @@ struct ip_vs_pe {
 	u32 (*hashkey_raw)(const struct ip_vs_conn_param *p, u32 initval,
 			   bool inverse);
 	int (*show_pe_data)(const struct ip_vs_conn *cp, char *buf);
+	/* create connections for real-server outgoing packets */
+	struct ip_vs_conn* (*conn_out)(struct ip_vs_service *svc,
+				       struct ip_vs_dest *dest,
+				       struct sk_buff *skb,
+				       const struct ip_vs_iphdr *iph,
+				       __be16 dport, __be16 cport);
 };
 
 /* The application module object (a.k.a. app incarnation) */
@@ -874,6 +880,7 @@ struct netns_ipvs {
 	/* Service counters */
 	atomic_t		ftpsvc_counter;
 	atomic_t		nullsvc_counter;
+	atomic_t		conn_out_counter;
 
 #ifdef CONFIG_SYSCTL
 	/* 1/rate drop and drop-entry variables */
@@ -1147,6 +1154,12 @@ static inline int sysctl_cache_bypass(struct netns_ipvs *ipvs)
  */
 const char *ip_vs_proto_name(unsigned int proto);
 void ip_vs_init_hash_table(struct list_head *table, int rows);
+struct ip_vs_conn *ip_vs_new_conn_out(struct ip_vs_service *svc,
+				      struct ip_vs_dest *dest,
+				      struct sk_buff *skb,
+				      const struct ip_vs_iphdr *iph,
+				      __be16 dport,
+				      __be16 cport);
 #define IP_VS_INIT_HASH_TABLE(t) ip_vs_init_hash_table((t), ARRAY_SIZE((t)))
 
 #define IP_VS_APP_TYPE_FTP	1
@@ -1378,6 +1391,10 @@ ip_vs_service_find(struct netns_ipvs *ipvs, int af, __u32 fwmark, __u16 protocol
 bool ip_vs_has_real_service(struct netns_ipvs *ipvs, int af, __u16 protocol,
 			    const union nf_inet_addr *daddr, __be16 dport);
 
+struct ip_vs_dest *
+ip_vs_find_real_service(struct netns_ipvs *ipvs, int af, __u16 protocol,
+			const union nf_inet_addr *daddr, __be16 dport);
+
 int ip_vs_use_count_inc(void);
 void ip_vs_use_count_dec(void);
 int ip_vs_register_nl_ioctl(void);

net/netfilter/ipvs/ip_vs_core.c

@@ -68,6 +68,7 @@ EXPORT_SYMBOL(ip_vs_conn_put);
 #ifdef CONFIG_IP_VS_DEBUG
 EXPORT_SYMBOL(ip_vs_get_debug_level);
 #endif
+EXPORT_SYMBOL(ip_vs_new_conn_out);
 
 static int ip_vs_net_id __read_mostly;
 /* netns cnt used for uniqueness */
@@ -1100,6 +1101,143 @@ static inline bool is_new_conn_expected(const struct ip_vs_conn *cp,
 	}
 }
 
+/* Generic function to create new connections for outgoing RS packets
+ *
+ * Pre-requisites for successful connection creation:
+ * 1) Virtual Service is NOT fwmark based:
+ *    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
+ */
+struct ip_vs_conn *ip_vs_new_conn_out(struct ip_vs_service *svc,
+				      struct ip_vs_dest *dest,
+				      struct sk_buff *skb,
+				      const struct ip_vs_iphdr *iph,
+				      __be16 dport,
+				      __be16 cport)
+{
+	struct ip_vs_conn_param param;
+	struct ip_vs_conn *ct = NULL, *cp = NULL;
+	const union nf_inet_addr *vaddr, *daddr, *caddr;
+	union nf_inet_addr snet;
+	__be16 vport;
+	unsigned int flags;
+
+	EnterFunction(12);
+	vaddr = &svc->addr;
+	vport = svc->port;
+	daddr = &iph->saddr;
+	caddr = &iph->daddr;
+
+	/* check pre-requisites are satisfied */
+	if (svc->fwmark)
+		return NULL;
+	if (!vport || !dport)
+		return NULL;
+
+	/* for persistent service first create connection template */
+	if (svc->flags & IP_VS_SVC_F_PERSISTENT) {
+		/* apply netmask the same way ingress-side does */
+#ifdef CONFIG_IP_VS_IPV6
+		if (svc->af == AF_INET6)
+			ipv6_addr_prefix(&snet.in6, &caddr->in6,
+					 (__force __u32)svc->netmask);
+		else
+#endif
+			snet.ip = caddr->ip & svc->netmask;
+		/* fill params and create template if not existent */
+		if (ip_vs_conn_fill_param_persist(svc, skb, iph->protocol,
+						  &snet, 0, vaddr,
+						  vport, &param) < 0)
+			return NULL;
+		ct = ip_vs_ct_in_get(&param);
+		if (!ct) {
+			ct = ip_vs_conn_new(&param, dest->af, daddr, dport,
+					    IP_VS_CONN_F_TEMPLATE, dest, 0);
+			if (!ct) {
+				kfree(param.pe_data);
+				return NULL;
+			}
+			ct->timeout = svc->timeout;
+		} else {
+			kfree(param.pe_data);
+		}
+	}
+
+	/* connection flags */
+	flags = ((svc->flags & IP_VS_SVC_F_ONEPACKET) &&
+		 iph->protocol == IPPROTO_UDP) ? IP_VS_CONN_F_ONE_PACKET : 0;
+	/* create connection */
+	ip_vs_conn_fill_param(svc->ipvs, svc->af, iph->protocol,
+			      caddr, cport, vaddr, vport, &param);
+	cp = ip_vs_conn_new(&param, dest->af, daddr, dport, flags, dest, 0);
+	if (!cp) {
+		if (ct)
+			ip_vs_conn_put(ct);
+		return NULL;
+	}
+	if (ct) {
+		ip_vs_control_add(cp, ct);
+		ip_vs_conn_put(ct);
+	}
+	ip_vs_conn_stats(cp, svc);
+
+	/* return connection (will be used to handle outgoing packet) */
+	IP_VS_DBG_BUF(6, "New connection RS-initiated:%c c:%s:%u v:%s:%u "
+		      "d:%s:%u conn->flags:%X conn->refcnt:%d\n",
+		      ip_vs_fwd_tag(cp),
+		      IP_VS_DBG_ADDR(cp->af, &cp->caddr), ntohs(cp->cport),
+		      IP_VS_DBG_ADDR(cp->af, &cp->vaddr), ntohs(cp->vport),
+		      IP_VS_DBG_ADDR(cp->af, &cp->daddr), ntohs(cp->dport),
+		      cp->flags, atomic_read(&cp->refcnt));
+	LeaveFunction(12);
+	return cp;
+}
+
+/* Handle outgoing packets which are considered requests initiated by
+ * real servers, so that subsequent responses from external client can be
+ * routed to the right real server.
+ * Used also for outgoing responses in OPS mode.
+ *
+ * Connection management is handled by persistent-engine specific callback.
+ */
+static struct ip_vs_conn *__ip_vs_rs_conn_out(unsigned int hooknum,
+					      struct netns_ipvs *ipvs,
+					      int af, struct sk_buff *skb,
+					      const struct ip_vs_iphdr *iph)
+{
+	struct ip_vs_dest *dest;
+	struct ip_vs_conn *cp = NULL;
+	__be16 _ports[2], *pptr;
+
+	if (hooknum == NF_INET_LOCAL_IN)
+		return NULL;
+
+	pptr = frag_safe_skb_hp(skb, iph->len,
+				sizeof(_ports), _ports, iph);
+	if (!pptr)
+		return NULL;
+
+	rcu_read_lock();
+	dest = ip_vs_find_real_service(ipvs, af, iph->protocol,
+				       &iph->saddr, pptr[0]);
+	if (dest) {
+		struct ip_vs_service *svc;
+		struct ip_vs_pe *pe;
+
+		svc = rcu_dereference(dest->svc);
+		if (svc) {
+			pe = rcu_dereference(svc->pe);
+			if (pe && pe->conn_out)
+				cp = pe->conn_out(svc, dest, skb, iph,
+						  pptr[0], pptr[1]);
+		}
+	}
+	rcu_read_unlock();
+
+	return cp;
+}
+
 /* Handle response packets: rewrite addresses and send away...
  */
 static unsigned int
@@ -1245,6 +1383,22 @@ ip_vs_out(struct netns_ipvs *ipvs, unsigned int hooknum, struct sk_buff *skb, in
 
 	if (likely(cp))
 		return handle_response(af, skb, pd, cp, &iph, hooknum);
+
+	/* Check for real-server-started requests */
+	if (atomic_read(&ipvs->conn_out_counter)) {
+		/* Currently only for UDP:
+		 * connection oriented protocols typically use
+		 * ephemeral ports for outgoing connections, so
+		 * related incoming responses would not match any VS
+		 */
+		if (pp->protocol == IPPROTO_UDP) {
+			cp = __ip_vs_rs_conn_out(hooknum, ipvs, af, skb, &iph);
+			if (likely(cp))
+				return handle_response(af, skb, pd, cp, &iph,
+						       hooknum);
+		}
+	}
+
 	if (sysctl_nat_icmp_send(ipvs) &&
 	    (pp->protocol == IPPROTO_TCP ||
 	     pp->protocol == IPPROTO_UDP ||

net/netfilter/ipvs/ip_vs_ctl.c

@@ -567,6 +567,36 @@ bool ip_vs_has_real_service(struct netns_ipvs *ipvs, int af, __u16 protocol,
 	return false;
 }
 
+/* Find real service record by <proto,addr,port>.
+ * In case of multiple records with the same <proto,addr,port>, only
+ * the first found record is returned.
+ *
+ * To be called under RCU lock.
+ */
+struct ip_vs_dest *ip_vs_find_real_service(struct netns_ipvs *ipvs, int af,
+					   __u16 protocol,
+					   const union nf_inet_addr *daddr,
+					   __be16 dport)
+{
+	unsigned int hash;
+	struct ip_vs_dest *dest;
+
+	/* Check for "full" addressed entries */
+	hash = ip_vs_rs_hashkey(af, daddr, dport);
+
+	hlist_for_each_entry_rcu(dest, &ipvs->rs_table[hash], d_list) {
+		if (dest->port == dport &&
+		    dest->af == af &&
+		    ip_vs_addr_equal(af, &dest->addr, daddr) &&
+			(dest->protocol == protocol || dest->vfwmark)) {
+			/* HIT */
+			return dest;
+		}
+	}
+
+	return NULL;
+}
+
 /* Lookup destination by {addr,port} in the given service
  * Called under RCU lock.
  */
@@ -1253,6 +1283,8 @@ ip_vs_add_service(struct netns_ipvs *ipvs, struct ip_vs_service_user_kern *u,
 		atomic_inc(&ipvs->ftpsvc_counter);
 	else if (svc->port == 0)
 		atomic_inc(&ipvs->nullsvc_counter);
+	if (svc->pe && svc->pe->conn_out)
+		atomic_inc(&ipvs->conn_out_counter);
 
 	ip_vs_start_estimator(ipvs, &svc->stats);
 
@@ -1293,6 +1325,7 @@ ip_vs_edit_service(struct ip_vs_service *svc, struct ip_vs_service_user_kern *u)
 	struct ip_vs_scheduler *sched = NULL, *old_sched;
 	struct ip_vs_pe *pe = NULL, *old_pe = NULL;
 	int ret = 0;
+	bool new_pe_conn_out, old_pe_conn_out;
 
 	/*
 	 * Lookup the scheduler, by 'u->sched_name'
@@ -1355,8 +1388,16 @@ ip_vs_edit_service(struct ip_vs_service *svc, struct ip_vs_service_user_kern *u)
 	svc->netmask = u->netmask;
 
 	old_pe = rcu_dereference_protected(svc->pe, 1);
-	if (pe != old_pe)
+	if (pe != old_pe) {
 		rcu_assign_pointer(svc->pe, pe);
+		/* check for optional methods in new pe */
+		new_pe_conn_out = (pe && pe->conn_out) ? true : false;
+		old_pe_conn_out = (old_pe && old_pe->conn_out) ? true : false;
+		if (new_pe_conn_out && !old_pe_conn_out)
+			atomic_inc(&svc->ipvs->conn_out_counter);
+		if (old_pe_conn_out && !new_pe_conn_out)
+			atomic_dec(&svc->ipvs->conn_out_counter);
+	}
 
 out:
 	ip_vs_scheduler_put(old_sched);
@@ -1389,6 +1430,8 @@ static void __ip_vs_del_service(struct ip_vs_service *svc, bool cleanup)
 
 	/* Unbind persistence engine, keep svc->pe */
 	old_pe = rcu_dereference_protected(svc->pe, 1);
+	if (old_pe && old_pe->conn_out)
+		atomic_dec(&ipvs->conn_out_counter);
 	ip_vs_pe_put(old_pe);
 
 	/*
@@ -3957,6 +4000,7 @@ int __net_init ip_vs_control_net_init(struct netns_ipvs *ipvs)
 		    (unsigned long) ipvs);
 	atomic_set(&ipvs->ftpsvc_counter, 0);
 	atomic_set(&ipvs->nullsvc_counter, 0);
+	atomic_set(&ipvs->conn_out_counter, 0);
 
 	/* procfs stats */
 	ipvs->tot_stats.cpustats = alloc_percpu(struct ip_vs_cpu_stats);

net/netfilter/ipvs/ip_vs_pe_sip.c

@@ -143,6 +143,20 @@ static int ip_vs_sip_show_pe_data(const struct ip_vs_conn *cp, char *buf)
 	return cp->pe_data_len;
 }
 
+static struct ip_vs_conn *
+ip_vs_sip_conn_out(struct ip_vs_service *svc,
+		   struct ip_vs_dest *dest,
+		   struct sk_buff *skb,
+		   const struct ip_vs_iphdr *iph,
+		   __be16 dport,
+		   __be16 cport)
+{
+	if (likely(iph->protocol == IPPROTO_UDP))
+		return ip_vs_new_conn_out(svc, dest, skb, iph, dport, cport);
+	/* currently no need to handle other than UDP */
+	return NULL;
+}
+
 static struct ip_vs_pe ip_vs_sip_pe =
 {
 	.name =			"sip",
@@ -153,6 +167,7 @@ static struct ip_vs_pe ip_vs_sip_pe =
 	.ct_match =		ip_vs_sip_ct_match,
 	.hashkey_raw =		ip_vs_sip_hashkey_raw,
 	.show_pe_data =		ip_vs_sip_show_pe_data,
+	.conn_out =		ip_vs_sip_conn_out,
 };
 
 static int __init ip_vs_sip_init(void)