From dfa486073cc3df1b9fae6fa41e238c52449fa1f6 Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Thu, 4 Feb 2016 13:31:18 +0100 Subject: [PATCH] ipv4: add option to drop gratuitous ARP packets In certain 802.11 wireless deployments, there will be ARP proxies that use knowledge of the network to correctly answer requests. To prevent gratuitous ARP frames on the shared medium from being a problem, on such deployments wireless needs to drop them. Enable this by providing an option called "drop_gratuitous_arp". Signed-off-by: Johannes Berg Signed-off-by: David S. Miller --- Documentation/networking/ip-sysctl.txt | 6 ++++++ include/uapi/linux/ip.h | 1 + net/ipv4/arp.c | 8 ++++++++ net/ipv4/devinet.c | 2 ++ 4 files changed, 17 insertions(+) diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt index d5910d63214d8..a53bbfaff1c74 100644 --- a/Documentation/networking/ip-sysctl.txt +++ b/Documentation/networking/ip-sysctl.txt @@ -1223,6 +1223,12 @@ drop_unicast_in_l2_multicast - BOOLEAN 1122, but is disabled by default for compatibility reasons. Default: off (0) +drop_gratuitous_arp - BOOLEAN + Drop all gratuitous ARP frames, for example if there's a known + good ARP proxy on the network and such frames need not be used + (or in the case of 802.11, must not be used to prevent attacks.) + 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 584834f7e95c9..f291569768ddf 100644 --- a/include/uapi/linux/ip.h +++ b/include/uapi/linux/ip.h @@ -166,6 +166,7 @@ enum IPV4_DEVCONF_IGMPV3_UNSOLICITED_REPORT_INTERVAL, IPV4_DEVCONF_IGNORE_ROUTES_WITH_LINKDOWN, IPV4_DEVCONF_DROP_UNICAST_IN_L2_MULTICAST, + IPV4_DEVCONF_DROP_GRATUITOUS_ARP, __IPV4_DEVCONF_MAX }; diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c index 59b3e0e8fd511..c102eb5ac55c8 100644 --- a/net/ipv4/arp.c +++ b/net/ipv4/arp.c @@ -735,6 +735,14 @@ static int arp_process(struct net *net, struct sock *sk, struct sk_buff *skb) (!IN_DEV_ROUTE_LOCALNET(in_dev) && ipv4_is_loopback(tip))) goto out; + /* + * For some 802.11 wireless deployments (and possibly other networks), + * there will be an ARP proxy and gratuitous ARP frames are attacks + * and thus should not be accepted. + */ + if (sip == tip && IN_DEV_ORCONF(in_dev, DROP_GRATUITOUS_ARP)) + goto out; + /* * Special case: We must set Frame Relay source Q.922 address */ diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c index dbbab28a52a49..3d835313575e0 100644 --- a/net/ipv4/devinet.c +++ b/net/ipv4/devinet.c @@ -2185,6 +2185,8 @@ static struct devinet_sysctl_table { "igmpv3_unsolicited_report_interval"), DEVINET_SYSCTL_RW_ENTRY(IGNORE_ROUTES_WITH_LINKDOWN, "ignore_routes_with_linkdown"), + DEVINET_SYSCTL_RW_ENTRY(DROP_GRATUITOUS_ARP, + "drop_gratuitous_arp"), DEVINET_SYSCTL_FLUSHING_ENTRY(NOXFRM, "disable_xfrm"), DEVINET_SYSCTL_FLUSHING_ENTRY(NOPOLICY, "disable_policy"), -- 2.39.5