[PATCH net-next v4] 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.

Signed-off-by: Erik Kline <redacted>
---
 Documentation/networking/ip-sysctl.txt |  7 +++++++
 include/linux/ipv6.h                   |  1 +
 include/uapi/linux/ipv6.h              |  1 +
 net/ipv6/addrconf.c                    | 22 +++++++++++++++++++---
 4 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index f63aeef..e710369 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt

@@ -1460,6 +1460,13 @@ router_solicitations - INTEGER
        routers are present.
        Default: 3

+use_oif_addr_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 1319a6b..28e4837 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h

@@ -57,6 +57,7 @@ struct ipv6_devconf {
                bool initialized;
                struct in6_addr secret;
        } stable_secret;
+       __s32           use_oif_addr_only;
        void            *sysctl;
 };

diff --git a/include/uapi/linux/ipv6.h b/include/uapi/linux/ipv6.h
index 5efa54a..6fcb256 100644
--- a/include/uapi/linux/ipv6.h
+++ b/include/uapi/linux/ipv6.h

@@ -171,6 +171,7 @@ enum {
        DEVCONF_USE_OPTIMISTIC,
        DEVCONF_ACCEPT_RA_MTU,
        DEVCONF_STABLE_SECRET,
+       DEVCONF_USE_OIF_ADDR_ONLY,
        DEVCONF_MAX
 };

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 32153c2..ebfb38a 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c

@@ -211,7 +211,8 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
        .accept_ra_mtu          = 1,
        .stable_secret          = {
                .initialized = false,
-       }
+       },
+       .use_oif_addr_only      = 0,
 };

 static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {

@@ -253,6 +254,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
        .stable_secret          = {
                .initialized = false,
        },
+       .use_oif_addr_only      = 0,
 };

 /* Check if a valid qdisc is available */

@@ -1472,11 +1474,16 @@ 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_addr_only)) {
                        use_oif_addr = true;
                }
        }

@@ -4607,6 +4614,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
        array[DEVCONF_ACCEPT_RA_FROM_LOCAL] = cnf->accept_ra_from_local;
        array[DEVCONF_ACCEPT_RA_MTU] = cnf->accept_ra_mtu;
        /* we omit DEVCONF_STABLE_SECRET for now */
+       array[DEVCONF_USE_OIF_ADDR_ONLY] = cnf->use_oif_addr_only;
 }

 static inline size_t inet6_ifla6_size(void)

@@ -5606,6 +5614,14 @@ static struct addrconf_sysctl_table
                        .proc_handler   = addrconf_sysctl_stable_secret,
                },
                {
+                       .procname       = "use_oif_addr_only",
+                       .data           = &ipv6_devconf.use_oif_addr_only,
+                       .maxlen         = sizeof(int),
+                       .mode           = 0644,
+                       .proc_handler   = proc_dointvec,
+
+               },
+               {
                        /* sentinel */
                }
        },
--

2.4.3.573.g4eafbef