netdev - Re: [PATCH net] ipv6: use rt6_info members when dst is set in rt6_fill

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Date:   Sun, 9 Sep 2018 14:29:19 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>,
        Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net] ipv6: use rt6_info members when dst is set in rt6_fill_node

On Sun, Sep 9, 2018 at 9:45 AM David Ahern <dsa@...ulusnetworks.com> wrote:
>
> On 9/8/18 3:24 AM, Xin Long wrote:
> > In inet6_rtm_getroute, since Commit 93531c674315 ("net/ipv6: separate
> > handling of FIB entries from dst based routes"), it has used rt->from
> > to dump route info instead of rt.
> >
> > However for some route like cache, its information is not the same as
> > that of the 'from' one. It caused 'ip -6 route get' to dump the wrong
> > route information.
> >
> > In Jianlin's testing, the output information even lost the expiration
> > time for a pmtu route cache due to the wrong fib6_flags.
>
> you are right about the flags ...
>
> >
> > So change to use rt6_info members when it tries to dump a route entry
> > without fibmatch set.
>
> but not the src, dst and prefsrc.
>
> >
> > Note that we will fix the gw/nh dump in another patch.
>
> And only the gateway can change do to a redirect and redirects do not
> change the device - only the gateway.
>
> Let's do both changes in a single patch.
>
> >
> > Fixes: 93531c674315 ("net/ipv6: separate handling of FIB entries from dst based routes")
> > Reported-by: Jianlin Shi <jishi@...hat.com>
> > Signed-off-by: Xin Long <lucien.xin@...il.com>
> > ---
> >  net/ipv6/route.c | 39 ++++++++++++++++++++++++++-------------
> >  1 file changed, 26 insertions(+), 13 deletions(-)
> >
> > diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> > index 18e00ce..e554922 100644
> > --- a/net/ipv6/route.c
> > +++ b/net/ipv6/route.c
> > @@ -4670,20 +4670,33 @@ static int rt6_fill_node(struct net *net, struct sk_buff *skb,
> >                        int iif, int type, u32 portid, u32 seq,
> >                        unsigned int flags)
> >  {
> > -     struct rtmsg *rtm;
> > +     struct rt6key *fib6_prefsrc, *fib6_dst, *fib6_src;
> > +     struct rt6_info *rt6 = (struct rt6_info *)dst;
> > +     u32 *pmetrics, table, fib6_flags;
> >       struct nlmsghdr *nlh;
> > +     struct rtmsg *rtm;
> >       long expires = 0;
> > -     u32 *pmetrics;
> > -     u32 table;
> >
> >       nlh = nlmsg_put(skb, portid, seq, type, sizeof(*rtm), flags);
> >       if (!nlh)
> >               return -EMSGSIZE;
> >
> > +     if (rt6) {
> > +             fib6_dst = &rt6->rt6i_dst;
> > +             fib6_src = &rt6->rt6i_src;
> > +             fib6_flags = rt6->rt6i_flags;
> > +             fib6_prefsrc = &rt6->rt6i_prefsrc;
> > +     } else {
> > +             fib6_dst = &rt->fib6_dst;
> > +             fib6_src = &rt->fib6_src;
> > +             fib6_flags = rt->fib6_flags;
> > +             fib6_prefsrc = &rt->fib6_prefsrc;
> > +     }
>
> Unless I am missing something at the moment, an rt6_info can only have
> the same dst, src and prefsrc as the fib6_info on which it is based.
> Thus, only the flags is needed above. That simplifies this patch a lot.
If dst, src and prefsrc in rt6_info are always the same as these in fib6_info,
why do we need them in rt6_info? we could just get it by 'from'.