netdev - Re: [PATCH net-next] ipv6: add debug checks in fib6_info

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Date: Thu, 7 Dec 2023 20:05:56 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Kui-Feng Lee <sinquersw@...il.com>
Cc: David Ahern <dsahern@...nel.org>, patchwork-bot+netdevbpf@...nel.org, 
	Kui-Feng Lee <thinker.li@...il.com>, davem@...emloft.net, kuba@...nel.org, 
	pabeni@...hat.com, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next] ipv6: add debug checks in fib6_info_release()

On Thu, Dec 7, 2023 at 8:00 PM Kui-Feng Lee <sinquersw@...il.com> wrote:
>
>
>
> On 12/7/23 10:40, Kui-Feng Lee wrote:
> >
> >
> > On 12/7/23 10:36, Kui-Feng Lee wrote:
> >>
> >>
> >> On 12/7/23 10:25, David Ahern wrote:
> >>> On 12/7/23 11:22 AM, Eric Dumazet wrote:
> >>>> Feel free to amend the patch, but the issue is that we insert a fib
> >>>> gc_link to a list, then free the fi6 object without removing it first
> >>>> from the external list.
> >>>
> >>> yes, move the insert down:
> >>>
> >>> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> >>> index b132feae3393..7257ba0e72b7 100644
> >>> --- a/net/ipv6/route.c
> >>> +++ b/net/ipv6/route.c
> >>> @@ -3762,12 +3762,6 @@ static struct fib6_info
> >>> *ip6_route_info_create(struct fib6_config *cfg,
> >>>          if (cfg->fc_flags & RTF_ADDRCONF)
> >>>                  rt->dst_nocount = true;
> >>>
> >>> -       if (cfg->fc_flags & RTF_EXPIRES)
> >>> -               fib6_set_expires_locked(rt, jiffies +
> >>> -
> >>> clock_t_to_jiffies(cfg->fc_expires));
> >>> -       else
> >>> -               fib6_clean_expires_locked(rt);
> >>> -
> >>
> >> fib6_set_expires_locked() here actually doesn't insert a fib gc_link
> >> since rt->fib6_table is not assigned yet.  The gc_link will
> >> be inserted by fib6_add() being called later.
> >>
> >>
> >>>          if (cfg->fc_protocol == RTPROT_UNSPEC)
> >>>                  cfg->fc_protocol = RTPROT_BOOT;
> >>>          rt->fib6_protocol = cfg->fc_protocol;
> >>> @@ -3824,6 +3818,12 @@ static struct fib6_info
> >>> *ip6_route_info_create(struct fib6_config *cfg,
> >>>          } else
> >>>                  rt->fib6_prefsrc.plen = 0;
> >>>
> >>> +
> >>> +       if (cfg->fc_flags & RTF_EXPIRES)
> >>> +               fib6_set_expires_locked(rt, jiffies +
> >>> +
> >>> clock_t_to_jiffies(cfg->fc_expires));
> >>> +       else
> >>> +               fib6_clean_expires_locked(rt);
> >>>          return rt;
> >>>   out:
> >>>          fib6_info_release(rt);
> >>
> >> However, this should fix the warning messages.
> > Just realize this cause inserting the gc_link twice.  fib6_add()
> > will try to add it again!
>
> I made a minor change to the patch that fix warning messages
> provided by David Ahern. Will send an official patch later.
>
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -3762,17 +3762,10 @@ static struct fib6_info
> *ip6_route_info_create(struct fib6_config *cfg,
>          if (cfg->fc_flags & RTF_ADDRCONF)
>                  rt->dst_nocount = true;
>
> -       if (cfg->fc_flags & RTF_EXPIRES)
> -               fib6_set_expires_locked(rt, jiffies +
> -
> clock_t_to_jiffies(cfg->fc_expires));
> -       else
> -               fib6_clean_expires_locked(rt);
> -
>          if (cfg->fc_protocol == RTPROT_UNSPEC)
>                  cfg->fc_protocol = RTPROT_BOOT;
>          rt->fib6_protocol = cfg->fc_protocol;
>
> -       rt->fib6_table = table;
>          rt->fib6_metric = cfg->fc_metric;
>          rt->fib6_type = cfg->fc_type ? : RTN_UNICAST;
>          rt->fib6_flags = cfg->fc_flags & ~RTF_GATEWAY;
> @@ -3824,6 +3817,17 @@ static struct fib6_info
> *ip6_route_info_create(struct fib6_config *cfg,
>          } else
>                  rt->fib6_prefsrc.plen = 0;
>
> +       if (cfg->fc_flags & RTF_EXPIRES)
> +               fib6_set_expires_locked(rt, jiffies +
> +
> clock_t_to_jiffies(cfg->fc_expires));
> +       else
> +               fib6_clean_expires_locked(rt);

Note that I do not see why we call fib6_clean_expires_locked() on a
freshly allocated object.

f6i->expires should already be zero...

> +       /* Set fib6_table after fib6_set_expires_locked() to ensure the
> +        * gc_link is not inserted until fib6_add() is called to insert the
> +        * fib6_info to the fib.
> +        */
> +       rt->fib6_table = table;
> +
>          return rt;
>   out: