netdev - Re: [PATCH] net: ipv6: fix __rt6_purge_dflt_routers when forwarding is not set on all ifaces

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Date:   Tue, 1 Sep 2020 08:33:17 -0700
From:   Brian Vazquez <brianvv@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Brian Vazquez <brianvv.kernel@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        David Ahern <dsa@...ulusnetworks.com>
Subject: Re: [PATCH] net: ipv6: fix __rt6_purge_dflt_routers when forwarding
 is not set on all ifaces

On Tue, Sep 1, 2020 at 12:56 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Tue, Sep 1, 2020 at 8:58 AM Brian Vazquez <brianvv@...gle.com> wrote:
> >
> > The problem is exposed when the system has multiple ifaces and
> > forwarding is enabled on a subset of them, __rt6_purge_dflt_routers will
> > clean the default route on all the ifaces which is not desired.
> >
> > This patches fixes that by cleaning only the routes where the iface has
> > forwarding enabled.
> >
> > Fixes: 830218c1add1 ("net: ipv6: Fix processing of RAs in presence of VRF")
>
>
>
>
>
> > Cc: David Ahern <dsa@...ulusnetworks.com>
> > Signed-off-by: Brian Vazquez <brianvv@...gle.com>
> > ---
> >  net/ipv6/route.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> > index 5e7e25e2523a..41181cd489ea 100644
> > --- a/net/ipv6/route.c
> > +++ b/net/ipv6/route.c
> > @@ -4283,6 +4283,7 @@ static void __rt6_purge_dflt_routers(struct net *net,
> >                                      struct fib6_table *table)
> >  {
> >         struct fib6_info *rt;
> > +       bool deleted = false;
> >
> >  restart:
> >         rcu_read_lock();
> > @@ -4291,16 +4292,19 @@ static void __rt6_purge_dflt_routers(struct net *net,
> >                 struct inet6_dev *idev = dev ? __in6_dev_get(dev) : NULL;
> >
> >                 if (rt->fib6_flags & (RTF_DEFAULT | RTF_ADDRCONF) &&
> > -                   (!idev || idev->cnf.accept_ra != 2) &&
> > +                   (!idev || (idev->cnf.forwarding == 1 &&
> > +                              idev->cnf.accept_ra != 2)) &&
> >                     fib6_info_hold_safe(rt)) {
> >                         rcu_read_unlock();
> >                         ip6_del_rt(net, rt, false);
> > +                       deleted = true;
> >                         goto restart;
> >                 }
> >         }
> >         rcu_read_unlock();
> >
> > -       table->flags &= ~RT6_TABLE_HAS_DFLT_ROUTER;
> > +       if (deleted)
> > +               table->flags &= ~RT6_TABLE_HAS_DFLT_ROUTER;
>
>
> This seems wrong : We want to keep the flag set if at least one
> candidate route has not been deleted,
> so that next time rt6_purge_dflt_routers() is called, we can call
> __rt6_purge_dflt_routers() ?

Yes, you're right. Although current implementation doesn't hurt
because if any of those candidate routes were not deleted means that
they have accept_ra == 2 which overrules the router behaviour so we
won't clean the SLAAC anyway.