ipv6: Allow accepting RA from local IP addresses.

This can be used in virtual networking applications, and
may have other uses as well.  The option is disabled by
default.

A specific use case is setting up virtual routers, bridges, and
hosts on a single OS without the use of network namespaces or
virtual machines.  With proper use of ip rules, routing tables,
veth interface pairs and/or other virtual interfaces,
and applications that can bind to interfaces and/or IP addresses,
it is possibly to create one or more virtual routers with multiple
hosts attached.  The host interfaces can act as IPv6 systems,
with radvd running on the ports in the virtual routers.  With the
option provided in this patch enabled, those hosts can now properly
obtain IPv6 addresses from the radvd.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 23 insertions, 8 deletions

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 5667b30..358edd2 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -186,6 +186,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
 	.max_desync_factor	= MAX_DESYNC_FACTOR,
 	.max_addresses		= IPV6_MAX_ADDRESSES,
 	.accept_ra_defrtr	= 1,
+	.accept_ra_from_local	= 0,
 	.accept_ra_pinfo	= 1,
 #ifdef CONFIG_IPV6_ROUTER_PREF
 	.accept_ra_rtr_pref	= 1,
@@ -222,6 +223,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
 	.max_desync_factor	= MAX_DESYNC_FACTOR,
 	.max_addresses		= IPV6_MAX_ADDRESSES,
 	.accept_ra_defrtr	= 1,
+	.accept_ra_from_local	= 0,
 	.accept_ra_pinfo	= 1,
 #ifdef CONFIG_IPV6_ROUTER_PREF
 	.accept_ra_rtr_pref	= 1,
@@ -4321,6 +4323,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
 	array[DEVCONF_FORCE_TLLAO] = cnf->force_tllao;
 	array[DEVCONF_NDISC_NOTIFY] = cnf->ndisc_notify;
 	array[DEVCONF_SUPPRESS_FRAG_NDISC] = cnf->suppress_frag_ndisc;
+	array[DEVCONF_ACCEPT_RA_FROM_LOCAL] = cnf->accept_ra_from_local;
 }
 
 static inline size_t inet6_ifla6_size(void)
@@ -5168,6 +5171,13 @@ static struct addrconf_sysctl_table
 			.proc_handler	= proc_dointvec
 		},
 		{
+			.procname	= "accept_ra_from_local",
+			.data		= &ipv6_devconf.accept_ra_from_local,
+			.maxlen		= sizeof(int),
+			.mode		= 0644,
+			.proc_handler	= proc_dointvec,
+		},
+		{
 			/* sentinel */
 		}
 	},
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 736c11c..a845e3d 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1148,11 +1148,15 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 		goto skip_defrtr;
 	}
 
-	if (ipv6_chk_addr(dev_net(in6_dev->dev), &ipv6_hdr(skb)->saddr,
-			  NULL, 0)) {
+	/* Do not accept RA with source-addr found on local machine unless
+	 * accept_ra_from_local is set to true.
+	 */
+	if (!(in6_dev->cnf.accept_ra_from_local ||
+	      ipv6_chk_addr(dev_net(in6_dev->dev), &ipv6_hdr(skb)->saddr,
+			    NULL, 0))) {
 		ND_PRINTK(2, info,
-			  "RA: %s, chk_addr failed for dev: %s\n",
-			  __func__, skb->dev->name);
+			  "RA from local address detected on dev: %s: default router ignored\n",
+			  skb->dev->name);
 		goto skip_defrtr;
 	}
 
@@ -1290,11 +1294,12 @@ skip_linkparms:
 	}
 
 #ifdef CONFIG_IPV6_ROUTE_INFO
-	if (ipv6_chk_addr(dev_net(in6_dev->dev), &ipv6_hdr(skb)->saddr,
-			  NULL, 0)) {
+	if (!(in6_dev->cnf.accept_ra_from_local ||
+	      ipv6_chk_addr(dev_net(in6_dev->dev), &ipv6_hdr(skb)->saddr,
+			    NULL, 0))) {
 		ND_PRINTK(2, info,
-			  "RA: %s, chk-addr (route info) is false for dev: %s\n",
-			  __func__, skb->dev->name);
+			  "RA from local address detected on dev: %s: router info ignored.\n",
+			  skb->dev->name);
 		goto skip_routeinfo;
 	}