linux-kernel - [PATCH 4.19 05/51] neighbor: Call __ipv4_neigh_lookup_noref in neigh

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Date:   Sun,  9 Jun 2019 18:41:46 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alan Maguire <alan.maguire@...cle.com>,
        David Ahern <dsahern@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.19 05/51] neighbor: Call __ipv4_neigh_lookup_noref in neigh_xmit

From: David Ahern <dsahern@...il.com>

[ Upstream commit 4b2a2bfeb3f056461a90bd621e8bd7d03fa47f60 ]

Commit cd9ff4de0107 changed the key for IFF_POINTOPOINT devices to
INADDR_ANY but neigh_xmit which is used for MPLS encapsulations was not
updated to use the altered key. The result is that every packet Tx does
a lookup on the gateway address which does not find an entry, a new one
is created only to find the existing one in the table right before the
insert since arp_constructor was updated to reset the primary key. This
is seen in the allocs and destroys counters:
    ip -s -4 ntable show | head -10 | grep alloc

which increase for each packet showing the unnecessary overhread.

Fix by having neigh_xmit use __ipv4_neigh_lookup_noref for NEIGH_ARP_TABLE.

Fixes: cd9ff4de0107 ("ipv4: Make neigh lookup keys for loopback/point-to-point devices be INADDR_ANY")
Reported-by: Alan Maguire <alan.maguire@...cle.com>
Signed-off-by: David Ahern <dsahern@...il.com>
Tested-by: Alan Maguire <alan.maguire@...cle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/core/neighbour.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -30,6 +30,7 @@
 #include <linux/times.h>
 #include <net/net_namespace.h>
 #include <net/neighbour.h>
+#include <net/arp.h>
 #include <net/dst.h>
 #include <net/sock.h>
 #include <net/netevent.h>
@@ -2536,7 +2537,13 @@ int neigh_xmit(int index, struct net_dev
 		if (!tbl)
 			goto out;
 		rcu_read_lock_bh();
-		neigh = __neigh_lookup_noref(tbl, addr, dev);
+		if (index == NEIGH_ARP_TABLE) {
+			u32 key = *((u32 *)addr);
+
+			neigh = __ipv4_neigh_lookup_noref(dev, key);
+		} else {
+			neigh = __neigh_lookup_noref(tbl, addr, dev);
+		}
 		if (!neigh)
 			neigh = __neigh_create(tbl, addr, dev, false);
 		err = PTR_ERR(neigh);