ipv6: sysctl to restrict candidate source addresses

Per RFC 6724, section 4, "Candidate Source Addresses":

    It is RECOMMENDED that the candidate source addresses be the set
    of unicast addresses assigned to the interface that will be used
    to send to the destination (the "outgoing" interface).

Add a sysctl to enable this behaviour.

Change-Id: Ia7de62a93bed3baed596bc16ed471f2c73ed513f
Signed-off-by: Erik Kline <ek@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 27 insertions, 2 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 64a0fc5985d6..a9e8802b729c 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1378,6 +1378,13 @@ router_solicitations - INTEGER
 	routers are present.
 	Default: 3
 
+use_oif_addrs_only - BOOLEAN
+	When enabled, the candidate source addresses for destinations
+	routed via this interface are restricted to the set of addresses
+	configured on this interface (vis. RFC 6724, section 4).
+
+	Default: false
+
 use_tempaddr - INTEGER
 	Preference for Privacy Extensions (RFC3041).
 	  <= 0 : disable Privacy Extensions
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index b8476f016354..bac42ed3a579 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -53,6 +53,7 @@ struct ipv6_devconf {
 	__s32		force_tllao;
 	__s32           ndisc_notify;
 	__s32		suppress_frag_ndisc;
+	__s32		use_oif_addrs_only;
 	void		*sysctl;
 };
 
diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index 187d9f6ccb0a..3388b91f2972 100644
--- a/include/uapi/linux/ipv6.h
+++ b/include/uapi/linux/ipv6.h
@@ -166,6 +166,7 @@ enum {
 	DEVCONF_SUPPRESS_FRAG_NDISC,
 	DEVCONF_ACCEPT_RA_FROM_LOCAL,
 	DEVCONF_USE_OPTIMISTIC,
+	DEVCONF_USE_OIF_ADDRS_ONLY,
 	DEVCONF_MAX
 };
 
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 50dbb49b40ce..33ebe994d3a2 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -202,6 +202,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
 	.disable_ipv6		= 0,
 	.accept_dad		= 1,
 	.suppress_frag_ndisc	= 1,
+	.use_oif_addrs_only	= 0,
 };
 
 static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
@@ -240,6 +241,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
 	.disable_ipv6		= 0,
 	.accept_dad		= 1,
 	.suppress_frag_ndisc	= 1,
+	.use_oif_addrs_only	= 0,
 };
 
 /* Check if a valid qdisc is available */
@@ -1459,11 +1461,16 @@ int ipv6_dev_get_saddr(struct net *net, const struct net_device *dst_dev,
 	 *    include addresses assigned to interfaces
 	 *    belonging to the same site as the outgoing
 	 *    interface.)
+	 *  - "It is RECOMMENDED that the candidate source addresses
+	 *    be the set of unicast addresses assigned to the
+	 *    interface that will be used to send to the destination
+	 *    (the 'outgoing' interface)." (RFC 6724)
 	 */
 	if (dst_dev) {
+		idev = __in6_dev_get(dst_dev);
 		if ((dst_type & IPV6_ADDR_MULTICAST) ||
-		    dst.scope <= IPV6_ADDR_SCOPE_LINKLOCAL) {
-			idev = __in6_dev_get(dst_dev);
+		    dst.scope <= IPV6_ADDR_SCOPE_LINKLOCAL ||
+		    (idev && idev->cnf.use_oif_addrs_only)) {
 			use_oif_addr = true;
 		}
 	}
@@ -4437,6 +4444,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
 	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;
+	array[DEVCONF_USE_OIF_ADDRS_ONLY] = cnf->use_oif_addrs_only;
 }
 
 static inline size_t inet6_ifla6_size(void)
@@ -5321,6 +5329,14 @@ static struct addrconf_sysctl_table
 			.proc_handler	= proc_dointvec,
 		},
 		{
+			.procname       = "use_oif_addrs_only",
+			.data           = &ipv6_devconf.use_oif_addrs_only,
+			.maxlen         = sizeof(int),
+			.mode           = 0644,
+			.proc_handler   = proc_dointvec,
+
+		},
+		{
 			/* sentinel */
 		}
 	},