net: ipv6: mld: implement RFC3810 MLDv2 mode only

RFC3810, 10. Security Considerations says under subsection 10.1.
Query Message:

  A forged Version 1 Query message will put MLDv2 listeners on that
  link in MLDv1 Host Compatibility Mode. This scenario can be avoided
  by providing MLDv2 hosts with a configuration option to ignore
  Version 1 messages completely.

Hence, implement a MLDv2-only mode that will ignore MLDv1 traffic:

  echo 2 > /proc/sys/net/ipv6/conf/ethX/force_mld_version  or
  echo 2 > /proc/sys/net/ipv6/conf/all/force_mld_version

Note that <all> device has a higher precedence as it was previously
also the case in the macro MLD_V1_SEEN() that would "short-circuit"
if condition on <all> case.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 30 insertions, 4 deletions

diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 005b22fd6bcb..c916568d838a 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -1112,11 +1112,34 @@ static bool mld_marksources(struct ifmcaddr6 *pmc, int nsrcs,
         return true;
 }
 
+static int mld_force_mld_version(const struct inet6_dev *idev)
+{
+        /* Normally, both are 0 here. If enforcement to a particular is
+         * being used, individual device enforcement will have a lower
+         * precedence over 'all' device (.../conf/all/force_mld_version).
+         */
+
+        if (dev_net(idev->dev)->ipv6.devconf_all->force_mld_version != 0)
+                return dev_net(idev->dev)->ipv6.devconf_all->force_mld_version;
+        else
+                return idev->cnf.force_mld_version;
+}
+
+static bool mld_in_v2_mode_only(const struct inet6_dev *idev)
+{
+        return mld_force_mld_version(idev) == 2;
+}
+
+static bool mld_in_v1_mode_only(const struct inet6_dev *idev)
+{
+        return mld_force_mld_version(idev) == 1;
+}
+
 static bool mld_in_v1_mode(const struct inet6_dev *idev)
 {
-        if (dev_net(idev->dev)->ipv6.devconf_all->force_mld_version == 1)
-                return true;
-        if (idev->cnf.force_mld_version == 1)
+        if (mld_in_v2_mode_only(idev))
+                return false;
+        if (mld_in_v1_mode_only(idev))
                 return true;
         if (idev->mc_v1_seen && time_before(jiffies, idev->mc_v1_seen))
                 return true;
@@ -1223,7 +1246,6 @@ int igmp6_event_query(struct sk_buff *skb)
                 return -EINVAL;
 
         idev = __in6_dev_get(skb->dev);
-
         if (idev == NULL)
                 return 0;
 
@@ -1236,6 +1258,10 @@ int igmp6_event_query(struct sk_buff *skb)
                 return -EINVAL;
 
         if (len == MLD_V1_QUERY_LEN) {
+                /* Ignore v1 queries */
+                if (mld_in_v2_mode_only(idev))
+                        return 0;
+
                 /* MLDv1 router present */
                 max_delay = msecs_to_jiffies(ntohs(mld->mld_maxdelay));