ipv4 05/05: add sysctl to accept packets with local source addresses

commit 8ec1e0ebe26087bfc5c0394ada5feb5758014fc8
Author: Patrick McHardy <kaber@trash.net>
Date:   Thu Dec 3 12:16:35 2009 +0100

    ipv4: add sysctl to accept packets with local source addresses

    Change fib_validate_source() to accept packets with a local source address when
    the "accept_local" sysctl is set for the incoming inet device. Combined with the
    previous patches, this allows to communicate between multiple local interfaces
    over the wire.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -731,6 +731,12 @@ accept_source_route - BOOLEAN
 	default TRUE (router)
 		FALSE (host)
 
+accept_local - BOOLEAN
+	Accept packets with local source addresses. In combination with
+	suitable routing, this can be used to direct packets between two
+	local interfaces over the wire and have them accepted properly.
+	default FALSE
+
 rp_filter - INTEGER
 	0 - No source validation.
 	1 - Strict mode as defined in RFC3704 Strict Reverse Path

include/linux/inetdevice.h

@@ -83,6 +83,7 @@ static inline void ipv4_devconf_setall(struct in_device *in_dev)
 #define IN_DEV_RPFILTER(in_dev)		IN_DEV_MAXCONF((in_dev), RP_FILTER)
 #define IN_DEV_SOURCE_ROUTE(in_dev)	IN_DEV_ANDCONF((in_dev), \
 						       ACCEPT_SOURCE_ROUTE)
+#define IN_DEV_ACCEPT_LOCAL(in_dev)	IN_DEV_ORCONF((in_dev), ACCEPT_LOCAL)
 #define IN_DEV_BOOTP_RELAY(in_dev)	IN_DEV_ANDCONF((in_dev), BOOTP_RELAY)
 
 #define IN_DEV_LOG_MARTIANS(in_dev)	IN_DEV_ORCONF((in_dev), LOG_MARTIANS)

include/linux/sysctl.h

@@ -490,6 +490,7 @@ enum
 	NET_IPV4_CONF_PROMOTE_SECONDARIES=20,
 	NET_IPV4_CONF_ARP_ACCEPT=21,
 	NET_IPV4_CONF_ARP_NOTIFY=22,
+	NET_IPV4_CONF_ACCEPT_LOCAL=23,
 	__NET_IPV4_CONF_MAX
 };
 

kernel/sysctl_check.c

@@ -220,6 +220,7 @@ static const struct trans_ctl_table trans_net_ipv4_conf_vars_table[] = {
 	{ NET_IPV4_CONF_PROMOTE_SECONDARIES,	"promote_secondaries" },
 	{ NET_IPV4_CONF_ARP_ACCEPT,		"arp_accept" },
 	{ NET_IPV4_CONF_ARP_NOTIFY,		"arp_notify" },
+	{ NET_IPV4_CONF_ACCEPT_LOCAL,		"accept_local" },
 	{}
 };
 

net/ipv4/devinet.c

@@ -1468,6 +1468,7 @@ static struct devinet_sysctl_table {
 		DEVINET_SYSCTL_RW_ENTRY(SEND_REDIRECTS, "send_redirects"),
 		DEVINET_SYSCTL_RW_ENTRY(ACCEPT_SOURCE_ROUTE,
 					"accept_source_route"),
+		DEVINET_SYSCTL_RW_ENTRY(ACCEPT_LOCAL, "accept_local"),
 		DEVINET_SYSCTL_RW_ENTRY(PROXY_ARP, "proxy_arp"),
 		DEVINET_SYSCTL_RW_ENTRY(MEDIUM_ID, "medium_id"),
 		DEVINET_SYSCTL_RW_ENTRY(BOOTP_RELAY, "bootp_relay"),

net/ipv4/fib_frontend.c

@@ -241,16 +241,17 @@ int fib_validate_source(__be32 src, __be32 dst, u8 tos, int oif,
 			    .iif = oif };
 
 	struct fib_result res;
-	int no_addr, rpf;
+	int no_addr, rpf, accept_local;
 	int ret;
 	struct net *net;
 
-	no_addr = rpf = 0;
+	no_addr = rpf = accept_local = 0;
 	rcu_read_lock();
 	in_dev = __in_dev_get_rcu(dev);
 	if (in_dev) {
 		no_addr = in_dev->ifa_list == NULL;
 		rpf = IN_DEV_RPFILTER(in_dev);
+		accept_local = IN_DEV_ACCEPT_LOCAL(in_dev);
 	}
 	rcu_read_unlock();
 
@@ -260,8 +261,10 @@ int fib_validate_source(__be32 src, __be32 dst, u8 tos, int oif,
 	net = dev_net(dev);
 	if (fib_lookup(net, &fl, &res))
 		goto last_resort;
-	if (res.type != RTN_UNICAST)
+	if (res.type != RTN_UNICAST) {
+		if (res.type != RTN_LOCAL || !accept_local)
 			goto e_inval_res;
+	}
 	*spec_dst = FIB_RES_PREFSRC(res);
 	fib_combine_itag(itag, &res);
 #ifdef CONFIG_IP_ROUTE_MULTIPATH