Date:   Mon, 18 Jul 2022 12:58:33 -0400
From:   Jaehee <jhpark1013@...il.com>
To:     nicolas.dichtel@...nd.com
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        David Ahern <dsahern@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, shuah@...nel.org,
        linux-kernel@...r.kernel.org, Arun Ajith S <aajith@...sta.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Roopa Prabhu <roopa.prabhu@...il.com>,
        Andy Roulin <aroulin@...dia.com>,
        Stefano Brivio <sbrivio@...hat.com>
Subject: Re: [PATCH v3 net-next 2/3] net: ipv6: new accept_untracked_na option
 to accept na only if in-network

On Mon, Jul 18, 2022 at 4:35 AM Nicolas Dichtel
<nicolas.dichtel@...nd.com> wrote:
>
>
> Le 14/07/2022 à 01:40, Jaehee Park a écrit :
> > This patch adds a third knob, '2', which extends the
> > accept_untracked_na option to learn a neighbor only if the src ip is
> > in the same subnet as an address configured on the interface that
> > received the neighbor advertisement. This is similar to the arp_accept
> > configuration for ipv4.
> >
> > Signed-off-by: Jaehee Park <jhpark1013@...il.com>
> > Suggested-by: Roopa Prabhu <roopa@...dia.com>
> > ---
> >  Documentation/networking/ip-sysctl.rst | 51 +++++++++++++++-----------
> >  net/ipv6/addrconf.c                    |  2 +-
> >  net/ipv6/ndisc.c                       | 29 ++++++++++++---
> >  3 files changed, 55 insertions(+), 27 deletions(-)
> >
> > diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> > index 5c017fc1e24d..722ec4f491db 100644
> > --- a/Documentation/networking/ip-sysctl.rst
> > +++ b/Documentation/networking/ip-sysctl.rst
> > @@ -2483,27 +2483,36 @@ drop_unsolicited_na - BOOLEAN
> >
> >       By default this is turned off.
> >
> > -accept_untracked_na - BOOLEAN
> > -     Add a new neighbour cache entry in STALE state for routers on receiving a
> > -     neighbour advertisement (either solicited or unsolicited) with target
> > -     link-layer address option specified if no neighbour entry is already
> > -     present for the advertised IPv6 address. Without this knob, NAs received
> > -     for untracked addresses (absent in neighbour cache) are silently ignored.
> > -
> > -     This is as per router-side behaviour documented in RFC9131.
> > -
> > -     This has lower precedence than drop_unsolicited_na.
> > -
> > -     This will optimize the return path for the initial off-link communication
> > -     that is initiated by a directly connected host, by ensuring that
> > -     the first-hop router which turns on this setting doesn't have to
> > -     buffer the initial return packets to do neighbour-solicitation.
> > -     The prerequisite is that the host is configured to send
> > -     unsolicited neighbour advertisements on interface bringup.
> > -     This setting should be used in conjunction with the ndisc_notify setting
> > -     on the host to satisfy this prerequisite.
> > -
> > -     By default this is turned off.
> > +accept_untracked_na - INTEGER
> > +     Define behavior for accepting neighbor advertisements from devices that
> > +     are absent in the neighbor cache:
> > +
> > +     - 0 - (default) Do not accept unsolicited and untracked neighbor
> > +       advertisements.
> > +
> > +     - 1 - Add a new neighbor cache entry in STALE state for routers on
> > +       receiving a neighbor advertisement (either solicited or unsolicited)
> > +       with target link-layer address option specified if no neighbor entry
> > +       is already present for the advertised IPv6 address. Without this knob,
> > +       NAs received for untracked addresses (absent in neighbor cache) are
> > +       silently ignored.
> > +
> > +       This is as per router-side behavior documented in RFC9131.
> > +
> > +       This has lower precedence than drop_unsolicited_na.
> > +
> > +       This will optimize the return path for the initial off-link
> > +       communication that is initiated by a directly connected host, by
> > +       ensuring that the first-hop router which turns on this setting doesn't
> > +       have to buffer the initial return packets to do neighbor-solicitation.
> > +       The prerequisite is that the host is configured to send unsolicited
> > +       neighbor advertisements on interface bringup. This setting should be
> > +       used in conjunction with the ndisc_notify setting on the host to
> > +       satisfy this prerequisite.
> > +
> > +     - 2 - Extend option (1) to add a new neighbor cache entry only if the
> > +       source IP address is in the same subnet as an address configured on
> > +       the interface that received the neighbor advertisement.
> >
> >  enhanced_dad - BOOLEAN
> >       Include a nonce option in the IPv6 neighbor solicitation messages used for
> > diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> > index 88becb037eb6..6ed807b6c647 100644
> > --- a/net/ipv6/addrconf.c
> > +++ b/net/ipv6/addrconf.c
> > @@ -7042,7 +7042,7 @@ static const struct ctl_table addrconf_sysctl[] = {
> >               .data           = &ipv6_devconf.accept_untracked_na,
> >               .maxlen         = sizeof(int),
> >               .mode           = 0644,
> > -             .proc_handler   = proc_dointvec_minmax,
> > +             .proc_handler   = proc_dointvec,
> >               .extra1         = (void *)SYSCTL_ZERO,
> >               .extra2         = (void *)SYSCTL_ONE,
> Maybe keeping proc_dointvec_minmax with SYSCTL_TWO for extra2 is better to avoid
> accepting all values. It enables to add another value later.
>

Hi Nicolas, your suggested fix seems to work well in helping us avoid
accepting values >2. When I applied this change, and try to set
accept_untracked_na=3, it gives me a warning: "invalid argument" which
is the desired behavior, thanks! There might be a similar way for arp;
i'm looking for this now.

>
> Regards,
> Nicolas

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