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>

7 files changed, 39 insertions, 8 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index ab42c95f9985..10e216c6e05e 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/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.
 
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index c811300b0b0c..b0f2452f1d58 100644
--- a/include/linux/ipv6.h
+++ b/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
diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index 593b0e32d956..efa2666f4b8a 100644
--- a/include/uapi/linux/ipv6.h
+++ b/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
 };
 
diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h
index 6d6721341f49..43aaba1cc037 100644
--- a/include/uapi/linux/sysctl.h
+++ b/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
 };
 
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index 653cbbd9e7ad..e4ba9a5a5ccb 100644
--- a/kernel/sysctl_binary.c
+++ b/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" },
 	{}
 };
 
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 5667b3003af9..358edd2272ac 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 736c11c6d266..a845e3d2057e 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;
 	}