From 98f1b6eb4ec5a59482cb6f5ac11b671df8cc89fe Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Thu, 4 Feb 2016 13:31:17 +0100 Subject: [PATCH] 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. Change-Id: I8de9fa5bdbea0556802f2ee553d0e73c1349213e Reviewed-by: Julian Anastasov Signed-off-by: Johannes Berg Signed-off-by: David S. Miller --- Documentation/networking/ip-sysctl.txt | 8 ++++++++ include/uapi/linux/ip.h | 1 + net/ipv4/devinet.c | 2 ++ net/ipv4/ip_input.c | 25 ++++++++++++++++++++++++- 4 files changed, 35 insertions(+), 1 deletion(-) diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index 35e9d4030165..2dc947fa5ad8 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -1053,6 +1053,14 @@ disable_xfrm - BOOLEAN +drop_unicast_in_l2_multicast - BOOLEAN + Drop any unicast IP packets that are received in link-layer + multicast (or broadcast) frames. + This behavior (for multicast) is actually a SHOULD in RFC + 1122, but is disabled by default for compatibility reasons. + Default: off (0) + + tag - INTEGER Allows you to write a number, which can be used as required. Default value is 0. diff --git a/include/uapi/linux/ip.h b/include/uapi/linux/ip.h index 2fee45bdec0a..a948faea6257 100644 --- a/include/uapi/linux/ip.h +++ b/include/uapi/linux/ip.h @@ -162,6 +162,7 @@ enum IPV4_DEVCONF_SRC_VMARK, IPV4_DEVCONF_PROXY_ARP_PVLAN, IPV4_DEVCONF_ROUTE_LOCALNET, + IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST, __IPV4_DEVCONF_MAX }; diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c index e0eaf5161d14..238858a9276f 100644 --- a/net/ipv4/devinet.c +++ b/net/ipv4/devinet.c @@ -2118,6 +2118,8 @@ static struct devinet_sysctl_table { "promote_secondaries"), DEVINET_SYSCTL_FLUSHING_ENTRY(ROUTE_LOCALNET, "route_localnet"), + DEVINET_SYSCTL_FLUSHING_ENTRY(DROP_UNICAST_IN_L2_MULTICAST, + "drop_unicast_in_l2_multicast"), }, }; diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c index 43f70dcce9b2..15ce6ae210f5 100644 --- a/net/ipv4/ip_input.c +++ b/net/ipv4/ip_input.c @@ -357,9 +357,32 @@ static int ip_rcv_finish(struct sk_buff *skb) if (rt->rt_type == RTN_MULTICAST) { IP_UPD_PO_STATS_BH(dev_net(rt->dst.dev), IPSTATS_MIB_INMCAST, skb->len); - } else if (rt->rt_type == RTN_BROADCAST) + } else if (rt->rt_type == RTN_BROADCAST) { IP_UPD_PO_STATS_BH(dev_net(rt->dst.dev), 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);