netdev - Re: [PATCH iproute2] iproute get: force rtm_dst

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Date:   Sun, 24 Jan 2021 17:37:38 +0000
From:   Luca Boccassi <bluca@...ian.org>
To:     David Ahern <dsahern@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH iproute2] iproute get: force rtm_dst_len to 32/128

On Sun, 24 Jan 2021 at 17:26, David Ahern <dsahern@...il.com> wrote:
>
> On 1/24/21 8:53 AM, Luca Boccassi wrote:
> > Since NETLINK_GET_STRICT_CHK was enabled, the kernel rejects commands
> > that pass a prefix length, eg:
> >
> >  ip route get `1.0.0.0/1
> >   Error: ipv4: Invalid values in header for route get request.
> >  ip route get 0.0.0.0/0
> >   Error: ipv4: rtm_src_len and rtm_dst_len must be 32 for IPv4
>
> Those are not the best responses from the kernel for the mask setting. I
> should have been clearer about src and dst masks.
>
> >
> > Since there's no point in setting a rtm_dst_len that we know is going
> > to be rejected, just force it to the right value if it's passed on
> > the command line.
> >
> > Bug-Debian: https://bugs.debian.org/944730
> > Reported-By: Clément 'wxcafé' Hertling <wxcafe@...afe.net>
> > Signed-off-by: Luca Boccassi <bluca@...ian.org>
> > ---
> > As mentioned by David on:
> >
> > https://www.spinics.net/lists/netdev/msg624125.html
> >
> >  ip/iproute.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/ip/iproute.c b/ip/iproute.c
> > index ebb5f160..3646d531 100644
> > --- a/ip/iproute.c
> > +++ b/ip/iproute.c
> > @@ -2069,7 +2069,12 @@ static int iproute_get(int argc, char **argv)
> >                       if (addr.bytelen)
> >                               addattr_l(&req.n, sizeof(req),
> >                                         RTA_DST, &addr.data, addr.bytelen);
> > -                     req.r.rtm_dst_len = addr.bitlen;
> > +                     if (req.r.rtm_family == AF_INET)
> > +                             req.r.rtm_dst_len = 32;
> > +                     else if (req.r.rtm_family == AF_INET6)
> > +                             req.r.rtm_dst_len = 128;
> > +                     else
> > +                             req.r.rtm_dst_len = addr.bitlen;
> >                       address_found = true;
> >               }
> >               argc--; argv++;
> >
>
> Since the kernel used to blindly ignore the mask, having iproute2 fix it
> up seems acceptable.
>
> I think it would be good to educate the user about invalid settings as
> well - get them to fix scripts and mind set.

Sent v2 with a warning print to stderr.

Kind regards,
Luca Boccassi