[BIRD 2.0.x] Netlink: ignore dead routes

[Alexander Zubkov]

Hi all,

I'll pop up this old discussion. I've found a bug with bird handling
its routes when ignore_routes_with_linkdown is enabled. And I suspect
it is related to this patch.
The problem is that bird does not replace or delete the routes it
installed when they are marked as dead. For example if we stop it with
"graceful restart", the routes are left in the table and after we
start bird again with updated config, this old route remains in the
table. I can reproduce it with bird compiled from master branch now.
Now, that I have found this thread, I suppose, that this changes blind
bird for all such routes during the scan. As a result bird also
ignores its own routes (proto bird), which causes problems. I think
there should be an exception for the routes that are installed by bird
itself. They should not be exported to the other protocols anyway, I
suppose. So the original question of this thread should not be
affected.
Steps to reproduce follows. Output from 2 consoles is mixed here.
bird{1,2}.conf are attached, the second one has static routes
commented out. Prepare:

# ip netns add a
# ip netns exec a bash
# ip link set lo up
# ip link add type veth
# sysctl -w net.ipv4.conf.veth0.ignore_routes_with_linkdown=1
# ip link set veth0 up
# ip addr add 10.0.0.1/24 dev veth0

Test:

# ip ro
10.0.0.0/24 dev veth0 proto kernel scope link src 10.0.0.1 dead linkdown
# bird -d -l -c bird1.conf
bird: Chosen router ID 10.0.0.1 according to interface veth0
bird: Started
# ip ro
10.0.0.0/24 dev veth0 proto kernel scope link src 10.0.0.1 dead linkdown
192.168.1.0/24 via 10.0.0.2 dev veth0 proto bird metric 32 dead linkdown
192.168.2.0/24 dev lo proto bird scope link metric 32
# birdc -l graceful restart
BIRD 2.0.8 ready.
Graceful restart requested
bird: Shutting down for graceful restart
bird: Shutdown completed
# ip ro
10.0.0.0/24 dev veth0 proto kernel scope link src 10.0.0.1 dead linkdown
192.168.1.0/24 via 10.0.0.2 dev veth0 proto bird metric 32 dead linkdown
192.168.2.0/24 dev lo proto bird scope link metric 32
# bird -d -l -c bird2.conf -R
bird: Chosen router ID 10.0.0.1 according to interface veth0
bird: Graceful restart started
bird: Graceful restart done
bird: Started
# ip ro
10.0.0.0/24 dev veth0 proto kernel scope link src 10.0.0.1 dead linkdown
192.168.1.0/24 via 10.0.0.2 dev veth0 proto bird metric 32 dead
linkdown <---- tihs route should have been deleted

On Thu, Jan 14, 2021 at 4:22 AM Ondrej Zajicek <santiago at crfreenet.org> wrote:
>
> On Thu, Oct 22, 2020 at 04:16:36PM +0200, Vincent Bernat wrote:
> > With net.ipv4.conf.XXX.ignore_routes_with_linkdown sysctl, a user can
> > ensure the kernel does not use a route whose target interface is down.
> > The route is marked with a "dead"/RTNH_F_DEAD flag. Currently, BIRD
> > still uses and distributes this route. This patch just ignores such a
> > route.
>
> Hi
>
> (Noticed while looking for some missed / forgotten e-mails)
>
> Thanks, merged with some changes (handling of direct and multipath routes):
>
> https://gitlab.nic.cz/labs/bird/-/commit/df83f626973fda1e67769d295c47d4d246e4c1c4
>
>
> Although it would make sense to handle dead routes as withdraws instead
> of just ingore them (for async notification), it does not matter for sync
> scan, and as i noticed during testing, Linux kernel does not send async
> notifications (when the flag changes to dead) anyways, so it does not
> really matter.
>
>
> > This patch could be backported to 1.6.x.
> >
> > Signed-off-by: Vincent Bernat <vincent at bernat.ch>
> > ---
> >  sysdep/linux/netlink.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/sysdep/linux/netlink.c b/sysdep/linux/netlink.c
> > index f85bcf35685b..c28126510e6e 100644
> > --- a/sysdep/linux/netlink.c
> > +++ b/sysdep/linux/netlink.c
> > @@ -1690,6 +1690,9 @@ nl_parse_route(struct nl_parse_state *s, struct nlmsghdr *h)
> >         if (i->rtm_flags & RTNH_F_ONLINK)
> >           ra->nh.flags |= RNF_ONLINK;
> >
> > +          if (i->rtm_flags & RTNH_F_DEAD)
> > +            return;
> > +
> >         neighbor *nbr;
> >         nbr = neigh_find(&p->p, ra->nh.gw, ra->nh.iface,
> >                          (ra->nh.flags & RNF_ONLINK) ? NEF_ONLINK : 0);
> > --
> > 2.28.0
>
> --
> Elen sila lumenn' omentielvo
>
> Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
> OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
> "To err is human -- to blame it on a computer is even more so."
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