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authorSalam Noureddine <noureddine@aristanetworks.com>2013-12-24 14:17:02 -0800
committerDavid S. Miller <davem@davemloft.net>2014-01-02 00:08:38 -0500
commit56022a8fdd874c56bb61d8c82559e43044d1aa06 (patch)
treecf2b3afdd11d5a2a9244afcc36b22e11dfd69c3c
parente82435341ff08769b70400b72a7a8efda83c5014 (diff)
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 <noureddine@aristanetworks.com> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/ipv4/arp.c15
1 files 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.