[Pkg-utopia-maintainers] Bug#644912: ipv6 link-local doesn't work as lookup doesn't set scope id

[Jens B. Jorgensen]

Incidentally even /with/ my patch ping6 doesn't work. This is because
due to the innards of how libnss works only when _nss_X_gethostbyname4_r
is called is it possible to return the scope id--the outputs of the
_nss_X_gethostbyname2_r and _nss_X_gethostbyname_r do not include this
data--_nss_X_gethostbyname2 returns data through a struct hostent as
does _nss_X_gethostbyname_r and unfortunately libnss doesn't call
_nss_X_gethostbyname4_r unless address family is UNSPEC. Now... despite
this you can see from my previous email that I was able to get different
behavior, ie. I could pass AF_INET6 and still get back scopeid. I
believe this is because the previous result was cached, though I didn't
step through the code to verify this. If you're curious you should take
a look at http://osxr.org/glibc/source/sysdeps/posix/getaddrinfo.c.
You'll see there:

0838           /* gethostbyname4_r sends out parallel A and AAAA queries and
0839          is thus only suitable for PF_UNSPEC.  */
0840           if (req->ai_family == PF_UNSPEC)
0841         fct4 = __nss_lookup_function (nip, "gethostbyname4_r");
0842
0843           if (fct4 != NULL)
0844         {
0845           int herrno;
0846
0847           while (1)
0848             {
0849               rc = 0;
0850               status = DL_CALL_FCT (fct4, (name, pat, tmpbuf,
0851                            tmpbuflen, &rc, &herrno,

Seems to me it should try to use gethostbyname4 if address is family is
UNSPEC or INET6. I presume there was a reason but I certainly don't know
what it is. The code falls back on gethostbyname2 in any case if the
gethostbyname4 isn't available. This is all a bit messy because if at
the top level you call getaddrinfo you should get the resolution
functions that can return the data you asked for but... that's not the
way it is. glibc needs a fix but the code is pretty complex so I didn't
want to try to tackle that (getaddrinfo.c itself is 2664 lines)--plus
it's a bit more nasty to test ;-).

On Mon, 10 Oct 2011 19:04:41 +0200 =?UTF-8?B?U3RlZmFuIELDvGhsZXI=?=
<stbuehler at lighttpd.net> wrote:
> Package: libnss-mdns
> Tags: ipv6
> Version: 0.10-3.2
>
> Hi,
>
> libnss-mdns doesn't set the scope-id for link-local addresses, so
> something like
>
> $ ping6 example.local
> gives
> connect: Invalid argument
>
> while
> $ getent host example.local
> returns a valid link-local IPv6 address (fe80::...) and
> $ ping6 fe80::...%eth0
> works fine.
>
>
> I sent this nearly 2 years ago upstream per mail, but never got a
> response, and i couldn't find an upstream bug tracker.
>
>
>

--
Jens B. Jorgensen /jorgensen at kcg.com <mailto:jorgensen at kcg.com>/


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