in.c autoadding prefix route [PATCH]

[Max Laier]

On Wednesday 17 November 2004 23:02, Ruslan Ermilov wrote:
> On Wed, Nov 17, 2004 at 07:50:32PM +0300, Vladimir Grebenschikov wrote:
> > В чт, 11/11/2004 в 21:24 +0100, Max Laier пишет:
> > > All,
> > >
> > > I know I have sent this a couple of times before, but never got
> > > anywhere. This time I am set to commit!
> > >
> > > The attached patch (http://people.freebsd.org/~mlaier/in.c.patch)
> > > derived from WIDE via OpenBSD in.c, rev 1.21 improves the handling of
> > > automatic prefix routes.
> > >
> > > Right now you can't have two legs into the same network. If you want
> > > to, you must give on of the interfaces a host address only (netmask
> > > /32). This way it is not possible to hand over the route if one of the
> > > interfaces is "removed" (however this is done in the special case).
> > >
> > > The patch allows to add more than on IPv4 address with the same prefix.
> > > In the case that there is a route already, we leave it alone and add
> > > the new address without the IFA_ROUTE flag. When we remove an address
> > > later on, that has a route associated, we try to find an alternative
> > > address to use for the route and hand it over.
> > >
> > > This is required for CARP, but should be helpful for other situations
> > > as well.
> > >
> > > Any objections?
> >
> > This change actually broke one simple thing:
> >
> > # ifconfig lo0 alias 10.0.16.111/32
> > # ping 10.0.16.111
> > PING 10.0.16.111 (10.0.16.111): 56 data bytes
> > ping: sendto: No route to host
> > ^C
> > #
> >
> > You should (anyway should) add routing of interface address itself to
> > loop-back interface, like it usually done in all other cases.
> >
> > Please fix.
>
> This bug was borrowed from OpenBSD (they still have it).
> The problem is that in "struct in_ifaddr", initially
>
>  ia_ifa.ifa_addr points to ia_addr
>   - and -
>  ia_ifa.ifa_dstaddr points to ia_dstaddr
>
> and the IFF_LOOPBACK code in in_ifinit() just resets
> the ia_ifa.ifa_dstaddr pointer to point to ia_ifa.ifa_addr.
> But new in_addprefix() code ignores this fact, and just
> uses INET fields directly, i.e., ia_dstaddr (which happens
> to be 0.0.0.0).  Then all the havoc happens (it matches
> another interface address (ia_addr=127.0.0.1, ia_dstaddr=0)
> and refuses to install a host route.
>
> The fix is a one line change, and as I later found out,
> it also corresponds to NetBSD revision 1.83:
>
> http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/in.c.diff?r1=1.82&r2=
>1.83&cvsroot=netbsd
>
> %%%
> Index: in.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/netinet/in.c,v
> retrieving revision 1.78
> diff -u -p -r1.78 in.c
> --- in.c 12 Nov 2004 20:53:51 -0000 1.78
> +++ in.c 17 Nov 2004 21:42:44 -0000
> @@ -759,7 +759,7 @@ in_ifinit(ifp, ia, sin, scrub)
>    ia->ia_netbroadcast.s_addr =
>     htonl(ia->ia_net | ~ ia->ia_netmask);
>   } else if (ifp->if_flags & IFF_LOOPBACK) {
> -  ia->ia_ifa.ifa_dstaddr = ia->ia_ifa.ifa_addr;
> +  ia->ia_dstaddr = ia->ia_addr;
>    flags |= RTF_HOST;
>   } else if (ifp->if_flags & IFF_POINTOPOINT) {
>    if (ia->ia_dstaddr.sin_family != AF_INET)
> %%%
>
> An alternative would be to fix in_addprefix() to pay
> attention to ia_ifa pointers, but as this bug shows,
> this is error prone.  It's much easier to just
> initialize the ia_dstaddr as appropriate.

Thanks. Good analysis ... I failed to see it :-\

I agree that setting ia_dstaddr is the less painful option.

Again, thanks a lot and sorry for the mess!

-- 
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