bug#41575: [bug#43371] [PATCH] doc: prevent host/container nscd mismatch

bug#41575: [bug#43371] [PATCH] doc: prevent host/container nscd mismatch

[conjaroy]

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Hello Ludo',

A separate nscd per container also seems like a reasonable option. However,
for the sake of machines hosting many long-lived containers, perhaps we
should consider reducing the cache size: currently it's 32MB for each name
service type, with an expiration of 12-24 hours:

https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/services/base.scm?id=1042d269a723360a02b19a2baafef1e24a3bfc73#n1115

Cheers,

Jason

On Sun, Sep 13, 2020 at 5:05 PM Ludovic Courtès <ludo@gnu.org> wrote:

> Hi,
>
> edk@beaver-labs.com skribis:
>
> > doc/guix.texi: (Name Service Switch) add a workaround for bug #41575
> > ---
> >  doc/guix.texi | 16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/doc/guix.texi b/doc/guix.texi
> > index a6e14ea177..a9472e680e 100644
> > --- a/doc/guix.texi
> > +++ b/doc/guix.texi
> > @@ -1706,6 +1706,20 @@ this binary incompatibility problem because those
> @code{libnss_*.so}
> >  files are loaded in the @command{nscd} process, not in applications
> >  themselves.
> >
> > +For applications running in containers (@pxref{Invokin guix container}),
> > +however, @code{nscd} may leak information from the host to the
> container.
> > +If there is a configuration mismatch between the two ---e.g., the host
> > +has no @code{sshd} user while the container needs one--- then it may be
>
> I find the example is hard to understand.  How about: “applications in
> the container could end up looking users in the host”?
>
> > +worthwhile to limit which kind of information the host's @code{nscd}
> > +daemon may give to the container by adding the following to
> > +@code{/etc/nscd.conf}.
> > +
> > +@example
> > +        enable-cache            passwd          no
> > +        enable-cache            group           no
> > +        enable-cache            netgroup        no
> > +@end example
>
> Actually, perhaps the better fix is to never use the host’s nscd?  We
> could change ‘containerized-operating-system’ accordingly.
>
> That would allow guest OSes to work correctly regardless of the host’s
> nscd config, which seems like an improvement.
>
> Thoughts?
>
> Ludo’.
>

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bug#41575: [bug#43371] [PATCH] doc: prevent host/container nscd mismatch

[Ludovic Courtès]

Hi,

conjaroy <conjaroy@gmail.com> skribis:

> A separate nscd per container also seems like a reasonable option. However,
> for the sake of machines hosting many long-lived containers, perhaps we
> should consider reducing the cache size: currently it's 32MB for each name
> service type, with an expiration of 12-24 hours:
>
> https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/services/base.scm?id=1042d269a723360a02b19a2baafef1e24a3bfc73#n1115

Good point.

In that case, we can have ‘containerized-operating-system’ provide its
own NSS configuration with a reduced cache size (or without cache since
there’s caching happening on the host for host name lookups, for
instance).

WDYT?  Would you like to give it a try?

Thanks,
Ludo’.

bug#41575: [bug#43371] [PATCH] doc: prevent host/container nscd mismatch

[Ludovic Courtès]

Hi,

Edouard Klein <edou@rdklein.fr> skribis:

>> Actually, perhaps the better fix is to never use the host’s nscd?  We
>> could change ‘containerized-operating-system’ accordingly.
>>
>
> I think this would be best, but I did not know where to make this
> change, so I just edited the doc instead. I don't know if containers
> need the host's nscd to avoid the libc issues mentionned in the doc, but
> if they dont, then prevening them from accessing the host's nscd seems
> logical and would solve the problem. And we wouldn't need to amend the
> doc at all.

This has now been done by Jason in
5627bfe45ce46f498979b4ad2deab1fdfed22b6c.

Closing!

Ludo’.