kern/51435: NetBSD-7 IPv6 addresses cannot be bound when "detached"

[Matthew Mondor <mm_lists%pulsar-zone.net@localhost>]

>Number:         51435
>Category:       kern
>Synopsis:       NetBSD-7 IPv6 addresses cannot be bound when "detached"
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Aug 22 08:10:00 +0000 2016
>Originator:     Matthew Mondor
>Release:        NetBSD 7.0_STABLE
>Organization:
>Environment:
System: NetBSD ninja.xisop 7.0_STABLE NetBSD 7.0_STABLE (GENERIC_MM) #0: Thu Jul 28 22:49:47 EDT 2016 root@ninja.xisop:/usr/obj/sys/arch/amd64/compile/GENERIC_MM amd64
Architecture: x86_64
Machine: amd64
>Description:

I noticed an issue on NetBSD-7 where IPv6 daemons would not be able to
bind to addresses.  This turned out to be because when the ethernet
port is disconnected, its associated address(es) get "detached", and
daemons get an error about the address being unavailable.

Apparently this would also be an issue with IPv4 on -current.  Please
see the thread "PATCH to mark IPv6 addresses DETACHED when down or link
down" on the tech-net mailing list for more information.

>How-To-Repeat:

ifconfig <if> inet6 <address> up
mkdir /tmp/www
<disconnect ethernet link temporarily>
httpd -b -i <address> -t /tmp/www -U _httpd -S 'httpd' -X /

>Fix:

It may be useful to allow binding to "detached" addresses.  Needing a
special socket option to allow it would still leave most daemons
broken, except those explicitely made to support this bug-mitigating
"feature".