From 56022a8fdd874c56bb61d8c82559e43044d1aa06 Mon Sep 17 00:00:00 2001 From: Salam Noureddine Date: Tue, 24 Dec 2013 14:17:02 -0800 Subject: [PATCH] ipv4: arp: update neighbour address when a gratuitous arp is received and arp_accept is set Gratuitous arp packets are useful in switchover scenarios to update client arp tables as quickly as possible. Currently, the mac address of a neighbour is only updated after a locktime period has elapsed since the last update. In most use cases such delays are unacceptable for network admins. Moreover, the "updated" field of the neighbour stucture doesn't record the last time the address of a neighbour changed but records any change that happens to the neighbour. This is clearly a bug since locktime uses that field as meaning "addr_updated". With this observation, I was able to perpetuate a stale address by sending a stream of gratuitous arp packets spaced less than locktime apart. With this change the address is updated when a gratuitous arp is received and the arp_accept sysctl is set. Signed-off-by: Salam Noureddine Acked-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- net/ipv4/arp.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c index 5bf408b466b1..1a9b99e04465 100644 --- a/net/ipv4/arp.c +++ b/net/ipv4/arp.c @@ -732,6 +732,7 @@ static int arp_process(struct sk_buff *skb) int addr_type; struct neighbour *n; struct net *net = dev_net(dev); + bool is_garp = false; /* arp_rcv below verifies the ARP header and verifies the device * is ARP'able. @@ -898,10 +899,12 @@ static int arp_process(struct sk_buff *skb) It is possible, that this option should be enabled for some devices (strip is candidate) */ + is_garp = arp->ar_op == htons(ARPOP_REQUEST) && tip == sip && + inet_addr_type(net, sip) == RTN_UNICAST; + if (n == NULL && - (arp->ar_op == htons(ARPOP_REPLY) || - (arp->ar_op == htons(ARPOP_REQUEST) && tip == sip)) && - inet_addr_type(net, sip) == RTN_UNICAST) + ((arp->ar_op == htons(ARPOP_REPLY) && + inet_addr_type(net, sip) == RTN_UNICAST) || is_garp)) n = __neigh_lookup(&arp_tbl, &sip, dev, 1); } @@ -914,8 +917,10 @@ static int arp_process(struct sk_buff *skb) agents are active. Taking the first reply prevents arp trashing and chooses the fastest router. */ - override = time_after(jiffies, n->updated + - NEIGH_VAR(n->parms, LOCKTIME)); + override = time_after(jiffies, + n->updated + + NEIGH_VAR(n->parms, LOCKTIME)) || + is_garp; /* Broadcast replies and request packets do not assert neighbour reachability. -- 2.20.1