From: Luca BRUNO <firstname.lastname@example.org>
Subject: Re: [musl] musl resolver handling of "search ." in /etc/resolv.conf
Date: Thu, 1 Sep 2022 16:03:18 +0000 [thread overview]
Message-ID: <20220901160318.67d15b3f@ephyra> (raw)
On Thu, 1 Sep 2022 08:45:12 -0400
Rich Felker <email@example.com> wrote:
> "search ." by itself is a semantically a no-op. It specifies a single
> search domain that's the DNS root, which is exactly what gets queried
> with no search at all. systemd is writing this into resolv.conf
> because of a glibc "misbehavior" (to put it lightly) where, in the
> absence of any search directive, it defaults to searching the domain
> of the system hostname (so hostname=foo.example.com would implicitly
> search example.com, which is obviously wrong to do, and systemd is
> trying to suppress that). But it would also cause failing lookups to
> be performed in duplicate, unless there's logic to suppress the final
> non-search lookup when root was already searched explicitly.
While tracking down this musl bug, I empirically observed from
network traces that glibc does apply such de-duplication logic under the
That is, it performs the root-anchored query in the specified order, and
in case of a negative response it does *not* perform the query again as
it would otherwise do for the final fallback case.
> > > There are 3 options I see:
> > >
> > > - Actually support it as a search. This is *bad* behavior, but at
> > > least unlike the version of this behavior musl explicitly does
> > > not implement, it was explicitly requested by the user. Except
> > > that it wasn't, because systemd is just putting it in everyone's
> > > resolv.conf..
> > >
> > > - Skip it completely. Never search root; wait for the end of the
> > > search list and query root as always.
> > >
> > > - End search on encountering it and go directly to the post-search
> > > query at root.
> > >
> > > Anyone care strongly about this one way or another?
From my observations, option 1 is consistent with other libc's behavior.
But it has the above caveat that it needs additional caching to
avoid duplicate root-queries on negative responses.
If it isn't too invasive to implement, that would be my preferred one.
Option 2 looks somehow reasonable too. The skewed order would be
a bit surprising, but it can be documented and it's unlikely to affect
many real-world usages.
next prev parent reply other threads:[~2022-09-01 16:04 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-31 17:33 Dalton Hubble
2022-08-31 23:59 ` Rich Felker
2022-09-01 1:32 ` Jeffrey Walton
2022-09-01 12:45 ` Rich Felker
2022-09-01 16:03 ` Luca BRUNO [this message]
2022-09-01 18:01 ` Rich Felker
2022-09-02 8:09 ` Luca BRUNO
2022-09-19 17:18 ` Rich Felker
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