ipv4: Make neigh lookup keys for loopback/point-to-point devices be INADDR_ANY

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 <jwestfall@surrealistic.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 9 insertions, 1 deletions

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 a8d7c5a9fb05..6c231b43974d 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) {