From: Johannes Berg <johannes.berg@xxxxxxxxx>
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 <johannes.berg@xxxxxxxxx>
---
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 a2169651254e..428fb48a19fc 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1215,6 +1215,12 @@ 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 584834f7e95c..f291569768dd 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 59b3e0e8fd51..36006a59c7f0 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 (IN_DEV_ORCONF(in_dev, DROP_GRATUITOUS_ARP) && sip == tip)
+ 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 dbbab28a52a4..3d835313575e 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"),
--
2.6.2
--
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