kern/145300: ARP table mapping is not refreshed on a MAC address change

[Boris Astardzhiev]

>Number:         145300
>Category:       kern
>Synopsis:       ARP table mapping is not refreshed on a MAC address change
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Fri Apr 02 17:00:13 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Boris Astardzhiev
>Release:        FreeBSD 8.0
>Organization:
Smartcom Bulgaria AD
>Environment:
FreeBSD boris-fbsd.smartcom.bg 8.0-RELEASE-p2 FreeBSD 8.0-RELEASE-p2 #3: Tue Mar 30 18:58:50 EEST 2010     root at boris-fbsd.smartcom.bg:/usr/src/sys/i386/compile/KGDB  i386

>Description:
On changing a link layer (MAC) address of a network interface that has an AF_INET address family applied to it the ARP table remains untouched reporting that the AF_INET address family is still mapped to the previous MAC address. An ARP table flush does not solve the problem.
>How-To-Repeat:
Here's a walk-through regarding the specified problem.

boris-fbsd# ifconfig em1
em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=9b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
	ether 08:00:27:07:bb:b7
	inet 192.168.56.2 netmask 0xffffff00 broadcast 192.168.56.255
	media: Ethernet autoselect (1000baseT <full-duplex>)
	status: active

boris-fbsd# arp -a -n
? (192.168.56.2) at 08:00:27:07:bb:b7 on em1 permanent [ethernet]

boris-fbsd# ifconfig em1 ether 11:22:33:44:55:66

boris-fbsd# ifconfig em1
em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=9b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
	ether 11:22:33:44:55:66
	inet 192.168.56.2 netmask 0xffffff00 broadcast 192.168.56.255
	media: Ethernet autoselect (1000baseT <full-duplex>)
	status: active

boris-fbsd# arp -a -n
? (192.168.56.2) at 08:00:27:07:bb:b7 on em1 permanent [ethernet]

boris-fbsd# arp -a -d
192.168.56.2 (192.168.56.2) deleted

boris-fbsd# arp -a -n
? (192.168.56.2) at 08:00:27:07:bb:b7 on em1 permanent [ethernet]

boris-fbsd# 

As you may have noticed the MAC address reported in the ARP table remains the old one though it's been changed.
>Fix:
A patch is applied.

Patch attached with submission follows:

--- usr/src/sys/net/if.c	2010-04-02 19:15:39.000000000 +0300
+++ /usr/src/sys/net/if.c	2010-04-02 19:16:57.000000000 +0300
@@ -142,6 +142,11 @@
 static void	if_attach_internal(struct ifnet *, int);
 static void	if_detach_internal(struct ifnet *, int);
 
+#ifdef INET
+/* XXX: better way to grab access to this function? */
+extern void arp_ifscrub(struct ifnet *ifp, uint32_t addr);
+#endif /* INET */
+
 #ifdef INET6
 /*
  * XXX: declare here to avoid to include many inet6 related files..
@@ -3197,8 +3202,14 @@
 		 * the address change.
 		 */
 		TAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
-			if (ifa->ifa_addr->sa_family == AF_INET)
+			if (ifa->ifa_addr->sa_family == AF_INET) {
+				struct in_ifaddr *ia = (struct in_ifaddr *)ifa;
+
+				/* Delete previous mappings in the ARP table 
+				 * first then send a gratuitous ARP */
+				arp_ifscrub(ifp, (uint32_t)(IA_SIN(ia)->sin_addr.s_addr));
 				arp_ifinit(ifp, ifa);
+			}
 		}
 #endif
 	}


>Release-Note:
>Audit-Trail:
>Unformatted: