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Old 07-07-2008, 03:49 AM
Aurelien Jarno
 
Default correct definition of localhost?

Steve Langasek a écrit :
> Hi folks,
>
> I've run across an ipv4/ipv6 configuration issue which I think needs to have
> light cast on it so we can try to resolve this in time for lenny (whatever
> the right resolution actually is), in order to avoid a pile-up of
> /etc/hosts-related kludges as has been known to happen before...
>
> In response to bug #427067, the netbase maintainer made a change that adds
> localhost as an alias for ::1 on new installs. In April of this year, the
> Debian Installer team followed suit, adding this line in the netcfg udeb.
>
> The result of these changes is that since July 2007, any new lenny or sid
> chroots have had two addresses listed for localhost, and since April of this
> year, any new installs of lenny done using d-i have had it as well.
>
> Now, the problem I ran into is that when I enabled the test suite in the
> openldap2.3 package, the build failed mysteriously on a seemingly random set
> of architectures. The reason? The test suite configures slapd to run on a
> particular port on localhost, and the glibc "files" NSS backend
> special-cases the ::1 IPv6 loopback address, so that when you request an
> IPv4 address, it will map any ::1 entries to 127.0.0.1 for you. But of
> course we already have an entry for localhost as 127.0.0.1, so now we end up
> with duplicate addresses returned, and slapd tries to bind twice to the same
> address and port!
>
> A test program showing this behavior is attached - compile and run it on a
> system with '::1 localhost' set in /etc/hosts, and you'll see 127.0.0.1
> returned twice. An alternate test case, which also works on systems with
> older /etc/hosts and which I think shows the counterintuitiveness of the
> nss_files special-casing, is to run "getent ahostsv4 ip6-localhost".
>
> I don't think it's the responsibility of callers such as slapd to check that
> getaddrinfo() hasn't returned duplicate entries, so I see a couple of
> solutions here:
>
> - the ::1 address should *not* be special-cased by nss_files. I really
> can't perceive any reason why it should be special-cased in the first
> place; i.e., why should the files backend behave differently than the DNS
> backend, and why would we want names that were specifically assigned to
> ::1, including names like "ip6-loopback", to be automatically mapped to
> 127.0.0.1?
>
> - we should only set up a single 'localhost' entry in /etc/hosts, pointing
> at ::1, and let nss_files handle the mapping to 127.0.0.1 automatically.
>
> Are there other solutions that should be considered? Is one of these more
> acceptable than the other? To me it seems obvious that the best choice is
> to not treat the files backend specially in the first place, but I don't
> know the rationale behind this special-casing either.

There is a bug upstream, but marked as invalid:

http://sources.redhat.com/bugzilla/show_bug.cgi?id=4980

According to the upstream developer, there is a rationale for that, but
he never explained it, despite having been asked numerous times.

Somebody has published a patch, if it works as expected, it may be worth
to include it in Debian.

Cheers,
Aurelien

--
.'`. Aurelien Jarno | GPG: 1024D/F1BCDB73
: :' : Debian developer | Electrical Engineer
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Old 07-07-2008, 06:15 AM
Kurt Roeckx
 
Default correct definition of localhost?

On Sun, Jul 06, 2008 at 05:14:44PM -0700, Steve Langasek wrote:
> On Mon, Jul 07, 2008 at 01:39:37AM +0200, Kurt Roeckx wrote:
>
> > You don't seem to request ipv4 addresses, you request AF_UNSPEC, which
> > should get you both ipv4 and ipv6. You get 127.0.0.1 twice, and ::1 one
> > time.
>
> You'll find that the duplication of 127.0.0.1 is still there if you specify
> AF_INET instead, because the problematic duplication happens when requesting
> records for the ipv4 address family. I left it as AF_UNSPEC in the test
> case to show that the problem exists when using protocol-agnostic best
> practices, which is what slapd does.

I was just confused when reading it, and understood it as only
requesting AF_INET. That was just to make it clear.

> >> - the ::1 address should *not* be special-cased by nss_files. I really
> >> can't perceive any reason why it should be special-cased in the first
> >> place; i.e., why should the files backend behave differently than the DNS
> >> backend, and why would we want names that were specifically assigned to
> >> ::1, including names like "ip6-loopback", to be automatically mapped to
> >> 127.0.0.1?
>
> > I can't find any good reason why it should be changing ::1 to 127.0.0.1.
> > So I think that atleast glibc should stop doing that. In any case, it
> > shouldn't return 127.0.0.1 twice when it's not configured to return
> > it twice.
>
> What do you mean by "configured to return it twice"? Would that mean
> duplicate lines in /etc/hosts (i.e., misconfiguration)?

Yes.

> >> - we should only set up a single 'localhost' entry in /etc/hosts, pointing
> >> at ::1, and let nss_files handle the mapping to 127.0.0.1 automatically.
>
> > - You could also argue that openldap should get fixed to deal with cases
> > where it tries to bind to the same ip/port twice. On the other hand,
> > I don't think it a normal case, and I think it's unlikely that people
> > would set up dns to have 2 times the same IP address and then try
> > to bind to that hostname.
>
> Well, as I said before,
>
> >> I don't think it's the responsibility of callers such as slapd to check that
> >> getaddrinfo() hasn't returned duplicate entries [...]
>
> so if you have an argument of why extra complexity should be added to the
> caller to deal with duplicate records which, one way or another, should not
> exist (IMHO), I'm interested to hear it.

The only case I can come up with would be misconfiguration, which I
don't think is a good reason.


Kurt


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Old 07-07-2008, 08:23 AM
Michael Banck
 
Default correct definition of localhost?

On Mon, Jul 07, 2008 at 05:49:04AM +0200, Aurelien Jarno wrote:
> There is a bug upstream, but marked as invalid:
>
> http://sources.redhat.com/bugzilla/show_bug.cgi?id=4980
>
> According to the upstream developer, there is a rationale for that, but
> he never explained it, despite having been asked numerous times.

In his latest reply, the upstream developer said that code got rewritten
since, I have not checked their repository though.


Michael


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Old 07-07-2008, 04:05 PM
Aurelien Jarno
 
Default correct definition of localhost?

Michael Banck a écrit :
> On Mon, Jul 07, 2008 at 05:49:04AM +0200, Aurelien Jarno wrote:
>> There is a bug upstream, but marked as invalid:
>>
>> http://sources.redhat.com/bugzilla/show_bug.cgi?id=4980
>>
>> According to the upstream developer, there is a rationale for that, but
>> he never explained it, despite having been asked numerous times.
>
> In his latest reply, the upstream developer said that code got rewritten
> since, I have not checked their repository though.

I have just built a version from CVS, and I confirm the bug is fixed.
However I failed to find the commit(s) which fixed it, and anyway I
doubt it's a single commit. Therefore I don't think we can backport the
fix for lenny.

We can try to use the proposed 2.7 patch instead.

--
.'`. Aurelien Jarno | GPG: 1024D/F1BCDB73
: :' : Debian developer | Electrical Engineer
`. `' aurel32@debian.org | aurelien@aurel32.net
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Old 07-08-2008, 12:37 AM
Joey Hess
 
Default correct definition of localhost?

http://sourceware.org/bugzilla/show_bug.cgi?id=4980

--
see shy jo, Amazed to be able to both mindlessly forward links
from reddit and possibly contribute value this this
thread at the same time. Not amazed at Drepper's behavior,
particualarly.
 
Old 07-08-2008, 11:47 AM
"Martijn van Oosterhout"
 
Default correct definition of localhost?

On Tue, Jul 8, 2008 at 2:37 AM, Joey Hess <joeyh@debian.org> wrote:
> http://sourceware.org/bugzilla/show_bug.cgi?id=4980

I just find it wierd that there doesn't appear to be a single person
who can explain the reasoning for the change...

Have a nice day,
--
Martijn van Oosterhout <kleptog@gmail.com> http://svana.org/kleptog/


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Old 07-08-2008, 11:52 AM
Ralf Hildebrandt
 
Default correct definition of localhost?

* Martijn van Oosterhout <kleptog@gmail.com>:
> On Tue, Jul 8, 2008 at 2:37 AM, Joey Hess <joeyh@debian.org> wrote:
> > http://sourceware.org/bugzilla/show_bug.cgi?id=4980
>
> I just find it wierd that there doesn't appear to be a single person
> who can explain the reasoning for the change...

That bugtracker entry sure makes some interesting reading

--
Ralf Hildebrandt (i.A. des IT-Zentrums) Ralf.Hildebrandt@charite.de
Charite - Universitätsmedizin Berlin Tel. +49 (0)30-450 570-155
Gemeinsame Einrichtung von FU- und HU-Berlin Fax. +49 (0)30-450 570-962
IT-Zentrum Standort CBF send no mail to snickebo@charite.de


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Old 07-08-2008, 12:16 PM
Roger Leigh
 
Default correct definition of localhost?

On Tue, Jul 08, 2008 at 01:52:43PM +0200, Ralf Hildebrandt wrote:
> * Martijn van Oosterhout <kleptog@gmail.com>:
> > On Tue, Jul 8, 2008 at 2:37 AM, Joey Hess <joeyh@debian.org> wrote:
> > > http://sourceware.org/bugzilla/show_bug.cgi?id=4980
> >
> > I just find it wierd that there doesn't appear to be a single person
> > who can explain the reasoning for the change...
>
> That bugtracker entry sure makes some interesting reading

It brings back memories of

https://bugzilla.redhat.com/show_bug.cgi?id=119185
http://lwn.net/Articles/196523/

drepper's attitude is just as bad, even if the effects aren't quite so
severe in this case.


--
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Old 07-08-2008, 04:40 PM
Steve Langasek
 
Default correct definition of localhost?

On Tue, Jul 08, 2008 at 01:47:51PM +0200, Martijn van Oosterhout wrote:
> On Tue, Jul 8, 2008 at 2:37 AM, Joey Hess <joeyh@debian.org> wrote:
> > http://sourceware.org/bugzilla/show_bug.cgi?id=4980

> I just find it wierd that there doesn't appear to be a single person
> who can explain the reasoning for the change...

Ulrich made the change, and he's not exactly known for giving helpful
explanations. Apparently he thinks bug ping-pong is a better use of his
time.

--
Steve Langasek Give me a lever long enough and a Free OS
Debian Developer to set it on, and I can move the world.
Ubuntu Developer http://www.debian.org/
slangasek@ubuntu.com vorlon@debian.org


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Old 07-08-2008, 05:23 PM
sean finney
 
Default correct definition of localhost?

On Tuesday 08 July 2008 06:40:05 pm Steve Langasek wrote:

> Ulrich made the change, and he's not exactly known for giving helpful
> explanations. Apparently he thinks bug ping-pong is a better use of his
> time.

it sounds like we have another contender for the annual jörg schilling
award[1].


sean

[1] http://mako.cc/copyrighteous/images/trophy.png
 

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