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>

Documentation/networking/ip-sysctl.txt

@@ -1210,6 +1210,18 @@ accept_ra_defrtr - BOOLEAN
 	Functional default: enabled if accept_ra is enabled.
 			    disabled if accept_ra is disabled.
 
+accept_ra_from_local - BOOLEAN
+	Accept RA with source-address that is found on local machine
+        if the RA is otherwise proper and able to be accepted.
+        Default is to NOT accept these as it may be an un-intended
+        network loop.
+
+	Functional default:
+           enabled if accept_ra_from_local is enabled
+               on a specific interface.
+	   disabled if accept_ra_from_local is disabled
+               on a specific interface.
+
 accept_ra_pinfo - BOOLEAN
 	Learn Prefix Information in Router Advertisement.
 

include/linux/ipv6.h

@@ -39,6 +39,7 @@ struct ipv6_devconf {
 #endif
 	__s32		proxy_ndp;
 	__s32		accept_source_route;
+	__s32		accept_ra_from_local;
 #ifdef CONFIG_IPV6_OPTIMISTIC_DAD
 	__s32		optimistic_dad;
 #endif

include/uapi/linux/ipv6.h

@@ -163,6 +163,7 @@ enum {
 	DEVCONF_MLDV1_UNSOLICITED_REPORT_INTERVAL,
 	DEVCONF_MLDV2_UNSOLICITED_REPORT_INTERVAL,
 	DEVCONF_SUPPRESS_FRAG_NDISC,
+	DEVCONF_ACCEPT_RA_FROM_LOCAL,
 	DEVCONF_MAX
 };
 

include/uapi/linux/sysctl.h

@@ -568,6 +568,7 @@ enum {
 	NET_IPV6_ACCEPT_RA_RT_INFO_MAX_PLEN=22,
 	NET_IPV6_PROXY_NDP=23,
 	NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
+	NET_IPV6_ACCEPT_RA_FROM_LOCAL=26,
 	__NET_IPV6_MAX
 };
 

kernel/sysctl_binary.c

@@ -522,6 +522,7 @@ static const struct bin_table bin_net_ipv6_conf_var_table[] = {
 	{ CTL_INT,	NET_IPV6_ACCEPT_RA_RT_INFO_MAX_PLEN,	"accept_ra_rt_info_max_plen" },
 	{ CTL_INT,	NET_IPV6_PROXY_NDP,			"proxy_ndp" },
 	{ CTL_INT,	NET_IPV6_ACCEPT_SOURCE_ROUTE,		"accept_source_route" },
+	{ CTL_INT,	NET_IPV6_ACCEPT_RA_FROM_LOCAL,		"accept_ra_from_local" },
 	{}
 };
 

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)
@@ -5167,6 +5170,13 @@ static struct addrconf_sysctl_table
 			.mode		= 0644,
 			.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 */
 		}

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 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 	}
 
 #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;
 	}