[v2,4/4] arp: always override existing neigh entries with gratuitous ARP

Submitted by Ihar Hrachyshka on May 18, 2017, 7:41 p.m.

Details

Message ID e6632af3eda7467c9a61402e8561cef7d6b9d02b.1495136258.git.ihrachys@redhat.com
State Accepted
Delegated to: David Miller
Headers show

Commit Message

Ihar Hrachyshka May 18, 2017, 7:41 p.m.
Currently, when arp_accept is 1, we always override existing neigh
entries with incoming gratuitous ARP replies. Otherwise, we override
them only if new replies satisfy _locktime_ conditional (packets arrive
not earlier than _locktime_ seconds since the last update to the neigh
entry).

The idea behind locktime is to pick the very first (=> close) reply
received in a unicast burst when ARP proxies are used. This helps to
avoid ARP thrashing where Linux would switch back and forth from one
proxy to another.

This logic has nothing to do with gratuitous ARP replies that are
generally not aligned in time when multiple IP address carriers send
them into network.

This patch enforces overriding of existing neigh entries by all incoming
gratuitous ARP packets, irrespective of their time of arrival. This will
make the kernel honour all incoming gratuitous ARP packets.

Signed-off-by: Ihar Hrachyshka <ihrachys@redhat.com>
---
 net/ipv4/arp.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

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diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index c22103c..ae96e6f 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -863,16 +863,17 @@  static int arp_process(struct net *net, struct sock *sk, struct sk_buff *skb)
 
 	n = __neigh_lookup(&arp_tbl, &sip, dev, 0);
 
-	if (IN_DEV_ARP_ACCEPT(in_dev)) {
+	if (n || IN_DEV_ARP_ACCEPT(in_dev)) {
 		addr_type = -1;
+		is_garp = arp_is_garp(net, dev, &addr_type, arp->ar_op,
+				      sip, tip, sha, tha);
+	}
 
+	if (IN_DEV_ARP_ACCEPT(in_dev)) {
 		/* Unsolicited ARP is not accepted by default.
 		   It is possible, that this option should be enabled for some
 		   devices (strip is candidate)
 		 */
-		is_garp = arp_is_garp(net, dev, &addr_type, arp->ar_op,
-				      sip, tip, sha, tha);
-
 		if (!n &&
 		    (is_garp ||
 		     (arp->ar_op == htons(ARPOP_REPLY) &&