ipv4: add option to drop unicast encapsulated in L2 multicast

In order to solve a problem with 802.11, the so-called hole-196 attack,
add an option (sysctl) called "drop_unicast_in_l2_multicast" which, if
enabled, causes the stack to drop IPv4 unicast packets encapsulated in
link-layer multi- or broadcast frames. Such frames can (as an attack)
be created by any member of the same wireless network and transmitted
as valid encrypted frames since the symmetric key for broadcast frames
is shared between all stations.

Additionally, enabling this option provides compliance with a SHOULD
clause of RFC 1122.

Reviewed-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/uapi/linux/ip.h b/include/uapi/linux/ip.h
index 08f894d2ddbd..584834f7e95c 100644
--- a/include/uapi/linux/ip.h
+++ b/include/uapi/linux/ip.h
@@ -165,6 +165,7 @@ enum
         IPV4_DEVCONF_IGMPV2_UNSOLICITED_REPORT_INTERVAL,
         IPV4_DEVCONF_IGMPV3_UNSOLICITED_REPORT_INTERVAL,
         IPV4_DEVCONF_IGNORE_ROUTES_WITH_LINKDOWN,
+        IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST,
         __IPV4_DEVCONF_MAX
 };