kern/49507: bridge(4) doesn't extend the expire time of a MAC address entry that has traffic

[ozaki-r%netbsd.org@localhost]

>Number:         49507
>Category:       kern
>Synopsis:       bridge(4) doesn't extend the expire time of a MAC address entry that has traffic
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Dec 26 07:55:00 +0000 2014
>Originator:     Ryota Ozaki
>Release:        current
>Organization:
>Environment:
any
>Description:
The expire time of a cache entry in a bridge MAC address table is initialized
when the entry is created and never extended (except for "brconfig bridgeN static").
See bridge_rtupdate function.

I don't think it's expected behavior of such caches. The expire time of a cache entry
should be extended when a frame for the entry go through the bridge.

bridge(4) of OpenBSD has the same behavior as NetBSD (because their code is our
original). OTOH, FreeBSD's behavior is what I expect.
>How-To-Repeat:
Setup a bridge:
  ifconfig bridge0 create
  ifconfig bridge0 up
  brconfig bridge0 add wm1
  brconfig bridge0 add wm2

Send frames over the bridge.

Show entries:
  ifconfig bridge0

You can see expire times of all address caches are constantly decreasing
regardless of traffic.
>Fix:
diff --git a/sys/net/if_bridge.c b/sys/net/if_bridge.c
index 9d60662..de418d2 100644
--- a/sys/net/if_bridge.c
+++ b/sys/net/if_bridge.c
@@ -2093,6 +2093,9 @@ again:
                                brt->brt_expire = 0;
                        else
                                brt->brt_expire = time_uptime + sc->sc_brttimeout;
+               } else {
+                       if ((brt->brt_flags & IFBAF_TYPEMASK) == IFBAF_DYNAMIC)
+                               brt->brt_expire = time_uptime + sc->sc_brttimeout;
                }
        }
        BRIDGE_RT_REXIT(s);