Merge branch 'ipv4-Make-neigh-lookup-keys-for-loopback-point-to-point-devices-be-INADDR_ANY'

Jim Westfall says:

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

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

Not having this results in there being an arp entry for every remote ip
address that the device talks to.  Given a fairly active device it can
cause the arp table to become huge and/or having to add/purge large number
of entires to keep within table size thresholds.

$ ip -4 neigh show nud noarp | grep tun | wc -l
55850

$ lnstat -k arp_cache:entries,arp_cache:allocs,arp_cache:destroys -c 10
arp_cach|arp_cach|arp_cach|
 entries|  allocs|destroys|
   81493|620166816|620126069|
  101867|   10186|       0|
  113854|    5993|       0|
  118773|    2459|       0|
   27937|   18579|   63998|
   39256|    5659|       0|
   56231|    8487|       0|
   65602|    4685|       0|
   79697|    7047|       0|
   90733|    5517|       0|

v2:
 - fixes coding style issues
====================

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

1 files changed, 3 insertions, 0 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);
 }