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authorJohannes Berg <johannes.berg@intel.com>2016-02-04 13:31:17 +0100
committerDavid S. Miller <davem@davemloft.net>2016-02-11 04:27:35 -0500
commit12b74dfadb5a7a23baf4db941dc9fd9d371f249a (patch)
tree40009e4d2e0eb925967d1ffde4f0c3b415f47ee3 /net/ipv4/ip_input.c
parentMAINTAINERS: Update tg3 maintainer (diff)
downloadlinux-dev-12b74dfadb5a7a23baf4db941dc9fd9d371f249a.tar.xz
linux-dev-12b74dfadb5a7a23baf4db941dc9fd9d371f249a.zip
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>
Diffstat (limited to '')
-rw-r--r--net/ipv4/ip_input.c25
1 files changed, 24 insertions, 1 deletions
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index d77eb0c3b684..852002f64c68 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -362,8 +362,31 @@ static int ip_rcv_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
rt = skb_rtable(skb);
if (rt->rt_type == RTN_MULTICAST) {
IP_UPD_PO_STATS_BH(net, IPSTATS_MIB_INMCAST, skb->len);
- } else if (rt->rt_type == RTN_BROADCAST)
+ } else if (rt->rt_type == RTN_BROADCAST) {
IP_UPD_PO_STATS_BH(net, IPSTATS_MIB_INBCAST, skb->len);
+ } else if (skb->pkt_type == PACKET_BROADCAST ||
+ skb->pkt_type == PACKET_MULTICAST) {
+ struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
+
+ /* RFC 1122 3.3.6:
+ *
+ * When a host sends a datagram to a link-layer broadcast
+ * address, the IP destination address MUST be a legal IP
+ * broadcast or IP multicast address.
+ *
+ * A host SHOULD silently discard a datagram that is received
+ * via a link-layer broadcast (see Section 2.4) but does not
+ * specify an IP multicast or broadcast destination address.
+ *
+ * This doesn't explicitly say L2 *broadcast*, but broadcast is
+ * in a way a form of multicast and the most common use case for
+ * this is 802.11 protecting against cross-station spoofing (the
+ * so-called "hole-196" attack) so do it for both.
+ */
+ if (in_dev &&
+ IN_DEV_ORCONF(in_dev, DROP_UNICAST_IN_L2_MULTICAST))
+ goto drop;
+ }
return dst_input(skb);