Hello,
On Wed, 4 Nov 2015, Johannes Berg wrote:
> From: Johannes Berg <johannes.b...@intel.com>
>
> 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.
>
> Signed-off-by: Johannes Berg <johannes.b...@intel.com>
Patches 1 and 3 look correct to me,
Reviewed-by: Julian Anastasov <j...@ssi.bg>
If the patches are lost in the merge window you
can also consider one minor optimization, see below...
> ---
> Documentation/networking/ip-sysctl.txt | 7 +++++++
> include/uapi/linux/ip.h | 1 +
> net/ipv4/devinet.c | 2 ++
> net/ipv4/ip_input.c | 26 +++++++++++++++++++++++++-
> 4 files changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/networking/ip-sysctl.txt
> b/Documentation/networking/ip-sysctl.txt
> index 05915be86235..35c4c43dd8de 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1208,6 +1208,13 @@ promote_secondaries - BOOLEAN
> promote a corresponding secondary IP address instead of
> removing all the corresponding secondary IP addresses.
>
> +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.
> 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
> };
>
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index cebd9d31e65a..dbbab28a52a4 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -2192,6 +2192,8 @@ 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 b1209b63381f..a442b6bd9441 100644
> --- a/net/ipv4/ip_input.c
> +++ b/net/ipv4/ip_input.c
> @@ -359,8 +359,32 @@ 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 {
} else if (unlikely(skb->pkt_type != PACKET_HOST)) {
May be such check can save some cycles because
it is more common to see PACKET_HOST packets...
> + 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) &&
> + (skb->pkt_type == PACKET_BROADCAST ||
> + skb->pkt_type == PACKET_MULTICAST))
> + goto drop;
> + }
>
> return dst_input(skb);
>
> --
> 2.6.2
Regards
--
Julian Anastasov <j...@ssi.bg>
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