ipv6: 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 IPv6 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.

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>
(cherry picked from commit dede82143bf1bbf92ea73a519bb0298b19c56cb9)

Change-Id: I76c8f84b53e95c40ad3c2b5adac0ec4964cc920c

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 8bc88a6..be536ed 100644 (file)
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1699,6 +1699,12 @@ stable_secret - IPv6 address
 
        By default the stable secret is unset.
 
+drop_unicast_in_l2_multicast - BOOLEAN
+       Drop any unicast IPv6 packets that are received in link-layer
+       multicast (or broadcast) frames.
+
+       By default this is turned off.
+
 icmp/*:
 ratelimit - INTEGER
        Limit the maximal rates for sending ICMPv6 packets.

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 7631503..53e7b5b 100644 (file)
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -53,6 +53,7 @@ struct ipv6_devconf {
        __s32           mc_forwarding;
 #endif
        __s32           disable_ipv6;
+       __s32           drop_unicast_in_l2_multicast;
        __s32           accept_dad;
        __s32           force_tllao;
        __s32           ndisc_notify;

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index e1ee651..2cbe640 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4772,6 +4772,7 @@ static inline void ipv6_store_devconf(struct ipv6_devconf *cnf,
        array[DEVCONF_IGNORE_ROUTES_WITH_LINKDOWN] = cnf->ignore_routes_with_linkdown;
        /* we omit DEVCONF_STABLE_SECRET for now */
        array[DEVCONF_USE_OIF_ADDRS_ONLY] = cnf->use_oif_addrs_only;
+       array[DEVCONF_DROP_UNICAST_IN_L2_MULTICAST] = cnf->drop_unicast_in_l2_multicast;
 }
 
 static inline size_t inet6_ifla6_size(void)
@@ -5859,6 +5860,13 @@ static struct addrconf_sysctl_table
                        .proc_handler   = addrconf_sysctl_ignore_routes_with_linkdown,
                },
                {
+                       .procname       = "drop_unicast_in_l2_multicast",
+                       .data           = &ipv6_devconf.drop_unicast_in_l2_multicast,
+                       .maxlen         = sizeof(int),
+                       .mode           = 0644,
+                       .proc_handler   = proc_dointvec,
+               },
+               {
                        /* sentinel */
                }
        },

diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c
index 9075acf..31ac3c5 100644 (file)
--- a/net/ipv6/ip6_input.c
+++ b/net/ipv6/ip6_input.c
@@ -134,6 +134,16 @@ int ipv6_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt
            IPV6_ADDR_MC_SCOPE(&hdr->daddr) == 1)
                goto err;
 
+       /* If enabled, drop unicast packets that were encapsulated in link-layer
+        * multicast or broadcast to protected against the so-called "hole-196"
+        * attack in 802.11 wireless.
+        */
+       if (!ipv6_addr_is_multicast(&hdr->daddr) &&
+           (skb->pkt_type == PACKET_BROADCAST ||
+            skb->pkt_type == PACKET_MULTICAST) &&
+           idev->cnf.drop_unicast_in_l2_multicast)
+               goto err;
+
        /* RFC4291 2.7
         * Nodes must not originate a packet to a multicast address whose scope
         * field contains the reserved value 0; if such a packet is received, it