My pleasure, Edouard. Thanks for the doc update!

Jason

On Sun, Sep 13, 2020 at 6:39 AM <edk@beaver-labs.com> wrote:

> Thank you for this thourough investigation and for finding the
> workaround !
>
> I just submitted a patch to the doc based on your email.
>
> Cheers,
>
> Edouard.
> conjaroy writes:
>
> > In an eariler bug comment [1] I corroborated that nscd was leaking
> > /etc/passwd information from the host OS into the Guix container, and I
> > wondered aloud why the container would use the host OS's nscd if there
> was
> > a risk of this happening.
> >
> > I've looked into how Guix configures its own nscd, and it turns out that
> by
> > default it enables lookups only for `hosts` and `services` - not for
> > `passwd`, `group`, or `netgroup`. Presumably, then, this configuration is
> > sufficient for nscd to prevent the glibc compatibility issues described
> in
> > the manual [3].
> >
> > After adding the following 3 lines in nscd.conf on my foreign distro
> > (Debian 10) and restarting nscd, my Guix system containers were able to
> > boot successfully while talking to the daemon:
> >
> >         enable-cache            passwd          no
> >         enable-cache            group           no
> >         enable-cache            netgroup        no
> >
> > So I think the bug here is that the Guix manual page advising the use of
> > nscd on a foreign distro [3] doesn't elaborate on which types of service
> > lookups are safe to enable in the daemon. If Guix is used only to build
> and
> > run binaries then perhaps it could use nscd for all lookups, but this is
> > evidently not the case for Guix system containers.
> >
> >
> > Cheers,
> >
> > Jason
> >
> >
> > [1] https://www.mail-archive.com/bug-guix@gnu.org/msg19915.html
> > [2]
> >
> https://git.savannah.gnu.org/cgit/guix.git/tree/gnu/services/base.scm?h=version-1.1.0#n1238
> > [3] https://guix.gnu.org/manual/en/html_node/Application-Setup.html
> >
> > On Mon, Aug 24, 2020 at 11:15 PM conjaroy <conjaroy@gmail.com> wrote:
> >
> >> I've observed this error under similar circumstances: launching a guix
> >> system container script with network sharing enabled, on a foreign disto
> >> (Debian 10) with nscd running.
> >>
> >> Using `strace -f /gnu/store/...-run-container`, we can observe the
> >> container's lookup of user accounts via the foreign distro's nscd
> socket:
> >>
> >> [pid 16582] socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0)
> = 11
> >> [pid 16582] connect(11, {sa_family=AF_UNIX,
> >> sun_path="/var/run/nscd/socket"}, 110) = 0
> >> [pid 16582] sendto(11, "\2\0\0\0\0\0\0\0\t\0\0\0postgres\0", 21,
> >> MSG_NOSIGNAL, NULL, 0) = 21
> >> [pid 16582] poll([{fd=11, events=POLLIN|POLLERR|POLLHUP}], 1, 5000) = 1
> >> ([{fd=11, revents=POLLIN}])
> >> [pid 16582] read(11,
> >>
> "\2\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\377\377\377\377\377\377\377\377\0\0\0\0\0\0\0\0"...,
> >> 36) = 36
> >> [pid 16582] close(11)                   = 0
> >>
> >> Since the user ("postgres") is indeed missing in the foreign disto, the
> >> lookup fails. In this case, disabling nscd on the foreign distro allowed
> >> the container script to run without error.
> >>
> >> Based on comments in https://issues.guix.info/issue/28128, I see that
> it
> >> was a deliberate choice to bind-mount the foreign distro's nscd socket
> >> inside the container (instead of starting a separate containerized nscd
> >> instance). But I'm having trouble seeing why it's acceptable to leak
> state
> >> from the foreign distro's user space into the container. Is there
> something
> >> I'm missing?
> >>
> >> Cheers,
> >>
> >> Jason
> >>
>
>