Subject: [PATCH 02/37] ipv4: Make neigh lookup keys for loopback/point-to-point devices be INADDR_ANY

From: Jim Westfall <[email-masked]>
Date: Sun, 14 Jan 2018 04:18:51 -0800

[ Upstream commit cd9ff4de0107c65d69d02253bb25d6db93c3dbc1 ]

Map all lookup neigh keys to INADDR_ANY for loopback/point-to-point devices
to avoid making an entry for every remote ip the device needs to talk to.

This used the be the old behavior but became broken in a263b3093641f
(ipv4: Make neigh lookups directly in output packet path) and later removed
in 0bb4087cbec0 (ipv4: Fix neigh lookup keying over loopback/point-to-point
devices) because it was broken.

Signed-off-by: Jim Westfall <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 include/net/arp.h | 3 +++
 net/ipv4/arp.c    | 7 ++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/net/arp.h b/include/net/arp.h
index dc8cd47f883b..977aabfcdc03 100644
--- a/include/net/arp.h
+++ b/include/net/arp.h
@@ -20,6 +20,9 @@ static inline u32 arp_hashfn(const void *pkey, const struct net_device *dev, u32
 
 static inline struct neighbour *__ipv4_neigh_lookup_noref(struct net_device *dev, u32 key)
 {
+	if (dev->flags & (IFF_LOOPBACK | IFF_POINTOPOINT))
+		key = INADDR_ANY;
+
 	return ___neigh_lookup_noref(&arp_tbl, neigh_key_eq32, arp_hashfn, &key, dev);
 }
 
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 7c45b8896709..a1d1f50e0e19 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -223,11 +223,16 @@ static bool arp_key_eq(const struct neighbour *neigh, const void *pkey)
 
 static int arp_constructor(struct neighbour *neigh)
 {
-	__be32 addr = *(__be32 *)neigh->primary_key;
+	__be32 addr;
 	struct net_device *dev = neigh->dev;
 	struct in_device *in_dev;
 	struct neigh_parms *parms;
+	u32 inaddr_any = INADDR_ANY;
 
+	if (dev->flags & (IFF_LOOPBACK | IFF_POINTOPOINT))
+		memcpy(neigh->primary_key, &inaddr_any, arp_tbl.key_len);
+
+	addr = *(__be32 *)neigh->primary_key;
 	rcu_read_lock();
 	in_dev = __in_dev_get_rcu(dev);
 	if (!in_dev) {
-- 
2.14.3