From: Florian Weimer <fweimer@redhat.com>
To: DJ Delorie <dj@redhat.com>
Cc: libc-alpha@sourceware.org
Subject: Re: nsswitch: do not reload if "/" changes
Date: Mon, 18 Jan 2021 11:47:36 +0100 [thread overview]
Message-ID: <87o8hmr06v.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <xnft2zvyho.fsf@greed.delorie.com> (DJ Delorie's message of "Sun, 17 Jan 2021 20:13:07 -0500")
* DJ Delorie:
>> I have one remaining question: Should we load service modules after /
>> has changed? Disabling reloading brings us back to the old behavior in
>> terms of exposure to untrusted /, but maybe we can do even better and
>> stop loading service modules altogether? Assuming that this change is
>> compatible with init systems.
>
> This patch makes it "no worse than before" but I'm not sure we can make
> it better than before, because we have no hints that we're entering a
> container, and by the time we have, it's too late to load the right
> module. The options become (1) don't load the module and definitely
> fail, or (2) maybe load the module in the container and work (and,
> depending on your app, open a security hole?) (which is the "old way").
>
> We would either need a new API that says "about to enter container" (or
> hack into the namespace syscalls) or at least dlopen all mentioned
> modules when we parse nsswitch.conf
Are you concerned with the case that there are no NSS calls before
entering the container, so that we don't initialize anything at all?
> + /* Before we reload, verify that "/" hasn't changed. We assume that
> + errors here are very unlikely, but the chance that we're entering
> + a container is also very unlikely, so we err on the side of both
> + very unlikely things not happening at the same time. */
> + if (__stat64 ("/", &str) == 0)
Hmm. Upon second thought, I think this need to be made fail-closed by
disabling reload on stat failure. The two things aren't as unrelated as
one might think (chroot + truning on some security filter doesn't seem
to be uncommon). Now of course it's a bit unlikely that anything can be
loaded later if / can't be read, but is there a harm in macking this
explicity?
Thanks,
Florian
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next prev parent reply other threads:[~2021-01-18 10:47 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-16 0:59 DJ Delorie
2021-01-16 10:52 ` Florian Weimer
2021-01-18 1:13 ` DJ Delorie
2021-01-18 10:47 ` Florian Weimer [this message]
2021-01-18 18:20 ` DJ Delorie
2021-01-19 16:37 ` Florian Weimer
2021-01-22 19:10 ` [v2] " DJ Delorie
2021-01-26 9:58 ` Florian Weimer
2021-01-26 16:19 ` DJ Delorie
2021-01-26 16:30 ` Florian Weimer
2021-01-26 16:47 ` DJ Delorie
2021-01-27 17:28 ` Carlos O'Donell
2021-01-27 18:44 ` DJ Delorie
2021-01-28 0:31 ` Joseph Myers
2021-01-28 0:34 ` DJ Delorie
2021-01-28 0:39 ` Joseph Myers
2021-01-28 1:15 ` DJ Delorie
2021-01-18 12:42 ` Andreas Schwab
2021-01-18 12:53 ` Florian Weimer
2021-01-18 18:27 ` DJ Delorie
2021-01-18 15:59 ` Carlos O'Donell
2021-01-18 16:53 ` Florian Weimer
2021-01-19 14:30 ` Carlos O'Donell
2021-01-19 14:40 ` Florian Weimer
2021-01-18 18:35 ` DJ Delorie
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