netdev - [PATCH] ipv4: arp: process only if ipv4 address configured

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Date:	Wed, 12 Feb 2014 18:27:47 +0100
From:	Florian Westphal <fw@...len.de>
To:	netdev@...r.kernel.org
Cc:	Florian Westphal <fw@...len.de>
Subject: [PATCH] ipv4: arp: process only if ipv4 address configured

8030f54499925d073a88c09f ([IPV4] devinet: Register inetdev earlier.)
changed arp behaviour (2.6.22 onwards).

Before this, inetdev_init() was called only when the first address was
added to the interface, i.e. arp_process always dropped incoming arp
packets as __in_dev_get_rcu() returned NULL when no IP address was set
on the interface.

With >= 2.6.22 we now process arp packets even if no address is assigned.
It can cause issues if the machine has several interfaces in the same
segment; requests receive answers from multiple macs.

Signed-off-by: Florian Westphal <fw@...len.de>
---
IMO such configurations are just asking for trouble, but it used
to work on older kernels.  Do we care about such setups?

diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 1a9b99e..8a44ed2 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -738,7 +738,7 @@ static int arp_process(struct sk_buff *skb)
 	 * is ARP'able.
 	 */

-	if (in_dev == NULL)
+	if (in_dev == NULL || in_dev->ifa_list == NULL)
 		goto out;

 	arp = arp_hdr(skb);
-- 
1.8.1.5

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