ipvs: add sysctl to ignore tunneled packets

This is a way to avoid nasty routing loops when multiple ipvs instances can
forward to eachother.

Signed-off-by: Alex Gartrell <[e-mail]>
Signed-off-by: Simon Horman <[e-mail]>

Documentation/networking/ipvs-sysctl.txt

···
 	persistence template if it is to be used to schedule a new
 	connection and the destination server is quiescent.
 
+ignore_tunneled - BOOLEAN
+	0 - disabled (default)
+	not 0 - enabled
+
+	If set, ipvs will set the ipvs_property on all packets which are of
+	unrecognized protocols.  This prevents us from routing tunneled
+	protocols like ipip, which is useful to prevent rescheduling
+	packets that have been tunneled to the ipvs host (i.e. to prevent
+	ipvs routing loops when ipvs is also acting as a real server).
+
 nat_icmp_send - BOOLEAN
         0 - disabled (default)
         not 0 - enabled

include/net/ip_vs.h

···
 	int			sysctl_backup_only;
 	int			sysctl_conn_reuse_mode;
 	int			sysctl_schedule_icmp;
+	int			sysctl_ignore_tunneled;
 
 	/* ip_vs_lblc */
 	int			sysctl_lblc_expiration;
···
 	return ipvs->sysctl_schedule_icmp;
 }
 
+static inline int sysctl_ignore_tunneled(struct netns_ipvs *ipvs)
+{
+	return ipvs->sysctl_ignore_tunneled;
+}
+
 #else
 
 static inline int sysctl_sync_threshold(struct netns_ipvs *ipvs)
···
 }
 
 static inline int sysctl_schedule_icmp(struct netns_ipvs *ipvs)
+{
+	return 0;
+}
+
+static inline int sysctl_ignore_tunneled(struct netns_ipvs *ipvs)
 {
 	return 0;
 }

net/netfilter/ipvs/ip_vs_core.c

···
 
 	/* Protocol supported? */
 	pd = ip_vs_proto_data_get(net, iph.protocol);
-	if (unlikely(!pd))
+	if (unlikely(!pd)) {
+		/* The only way we'll see this packet again is if it's
+		 * encapsulated, so mark it with ipvs_property=1 so we
+		 * skip it if we're ignoring tunneled packets
+		 */
+		if (sysctl_ignore_tunneled(ipvs))
+			skb->ipvs_property = 1;
+
 		return NF_ACCEPT;
+	}
 	pp = pd->pp;
 	/*
 	 * Check if the packet belongs to an existing connection entry

net/netfilter/ipvs/ip_vs_ctl.c

···
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
+	{
+		.procname	= "ignore_tunneled",
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
 #ifdef CONFIG_IP_VS_DEBUG
 	{
 		.procname	= "debug_level",
···
 	ipvs->sysctl_conn_reuse_mode = 1;
 	tbl[idx++].data = &ipvs->sysctl_conn_reuse_mode;
 	tbl[idx++].data = &ipvs->sysctl_schedule_icmp;
+	tbl[idx++].data = &ipvs->sysctl_ignore_tunneled;
 
 	ipvs->sysctl_hdr = register_net_sysctl(net, "net/ipv4/vs", tbl);
 	if (ipvs->sysctl_hdr == NULL) {