Route export problem with FreeBSD 13.0

[Luiz Amaral]

Hello guys,

After upgrading one of my hosts from FreeBSD 12.2 to FreeBSD 13.0, I
started noticing a problem when exporting routes to the KRT.

My logs were getting flooded with "kernel: gw sdl_len too small". This
message comes from cleanup_xaddrs_gateway() in sys/net/rtsock.c of
releng/13.0, so I checked with "route monitor" and noticed that the
blackhole routes and one interface route were the ones causing the message.

got message of size 192 on Sat Aug 28 15:57:32 2021
RTM_ADD: Add Route: len 192, pid: 2293, seq 3, errno 22,
flags:<UP,BLACKHOLE,PROTO1>
locks:  inits:
sockaddrs: <DST,GATEWAY,NETMASK>
 10.0.0.0 link#4 255.0.0.0

got message of size 192 on Sat Aug 28 15:57:32 2021
RTM_ADD: Add Route: len 192, pid: 2293, seq 4, errno 22, flags:<UP,PROTO1>
locks:  inits:
sockaddrs: <DST,GATEWAY,NETMASK>
 10.42.10.0 link#5 255.255.255.0

In BIRD they look the same as before the upgrade:

bird> show route all 10.0.0.0/8
Table master4:
10.0.0.0/8           blackhole [s_null_4 2021-08-28 15:57:32] ! (200)
        Type: static univ
bird> show route all 10.42.10.0/24
Table master4:
10.42.10.0/24        unicast [direct1 2021-08-28 16:07:59] ! (240)
        dev vlan10
        Type: device univ


I then decided to try manually adding a blackhole route using "route add
-net 10.0.0.0/8 -blackhole -proto1 -nostatic", to get as close to what
BIRD was trying to add and noticed that BIRD had a gateway, but "route
add" didn't have one.

got message of size 184 on Sat Aug 28 16:05:43 2021
RTM_ADD: Add Route: len 184, pid: 2766, seq 1, errno 0,
flags:<UP,GATEWAY,DONE,BLACKHOLE,PROTO1>
locks:  inits:
sockaddrs: <DST,NETMASK>
 10.0.0.0 255.0.0.0

I tried commenting out line 324 in sysdep/bsd/krt-sock.c of v2.0.8 to
see if that could fix it and bird was able to insert the blackhole route
(can be seen below), but then bird started dying a couple seconds after
starting up, with no error showing up on the logs.

got message of size 184 on Sat Aug 28 15:27:33 2021
RTM_ADD: Add Route: len 184, pid: 46425, seq 2, errno 22, flags:<UP,PROTO1>
locks:  inits:
sockaddrs: <DST,NETMASK>
 10.42.10.0 255.255.255.0

got message of size 184 on Sat Aug 28 15:27:33 2021
RTM_ADD: Add Route: len 184, pid: 46425, seq 3, errno 0,
flags:<UP,GATEWAY,DONE,BLACKHOLE,PROTO1>
locks:  inits:
sockaddrs: <DST,NETMASK>
 10.0.0.0 255.0.0.0


At this point, I ran out of ideas on what else to try. This is in a
testing environment, so I can easily try things out or provide extra
information.

Thank you,
Luiz