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From: "Ludovic Courtès" <ludo@gnu.org>
To: Leo Famulari <leo@famulari.name>, Maxime Devos <maximedevos@telenet.be>
Cc: guix-devel@gnu.org
Subject: Re: Potential security weakness in Guix services
Date: Mon, 01 Feb 2021 16:35:56 +0100	[thread overview]
Message-ID: <87k0rrls0z.fsf@gnu.org> (raw)
In-Reply-To: <YBMybeFOP0VfW6G7@jasmine.lan> (Leo Famulari's message of "Thu, 28 Jan 2021 16:53:49 -0500")

Hi,

Leo Famulari <leo@famulari.name> skribis:

> For clarification: the scenario I currently have in mind, is that noone
> has intentionally introduced a security hole in a service, but rather
> there's an accidental security bug somewhere in service package, that
> allows an attacker (I'm assuming the service is accessible from the
> network) arbitrary code execution *within* the service's process.
>
> As it is now, the attacker could overtake the service process, then chown
> and chmod arbitrary directories from there. As a particular example, I'm
> considering e.g. a hypothetical ipfs-service-type. A compromised IPFS process
> shouldn't be able to change /etc/passwd entries. The security of the IPFS
> service itself shouldn't be critical to the security of the system as a
> whole.
> -----
>
> A more specific exapmle:
>
> ----- Forwarded message from Maxime Devos <maximedevos@telenet.be> -----
> I seem to have stumbled upon a potential security issue, it has to
> do with how some services use mkdir-p/perms. For example, in knot-activation:
>
>    (define (knot-activation config)
>      #~(begin
>          (use-modules (guix build utils))
>          (mkdir-p/perms #$(knot-configuration-run-directory config)
>                         (getpwnam "knot") #o755)
>          (mkdir-p/perms "/var/lib/knot" (getpwnam "knot") #o755)
>          (mkdir-p/perms "/var/lib/knot/keys" (getpwnam "knot") #o755)
>          (mkdir-p/perms "/var/lib/knot/keys/keys" (getpwnam "knot") #o755)))
>
> /var/lib/knot/keys/keys is chmodded and chowned, which seems innocent enough.
> However, what if knot whas compromised at some point, and the compromised knot
> process has replaced /var/lib/knot/keys with, say, a symlink to /gnu/store?

I’m not sure I understand the threat model.  If Knot has a RCE
vulnerability, it can be exploited to run anything on behalf of the
‘knot’ user.

At that point, all the state associated with Knot in /var/lib should be
considered tainted; new keys should be generated, and so on.

Why focus on the permissions on /var/lib/knot?

Also, every time it’s possible and not redundant with measures already
implemented by the daemon itself, we should consider using
‘make-forkexec-constructor/container’ as a further mitigation.

WDYT?

Ludo’.


  parent reply	other threads:[~2021-02-01 15:37 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-28 21:53 Potential security weakness in Guix services Leo Famulari
2021-01-29 13:33 ` Maxime Devos
2021-01-29 15:25   ` Maxime Devos
2021-02-01 15:35 ` Ludovic Courtès [this message]
2021-02-01 15:47   ` Julien Lepiller
2021-02-01 16:19     ` Maxime Devos
2021-02-02 13:07       ` Ludovic Courtès
2021-02-02 13:38         ` Maxime Devos
2021-02-02 15:30           ` Maxime Devos
2021-02-05  9:57           ` Ludovic Courtès
2021-02-05 12:20             ` Maxime Devos
2021-02-05 14:16               ` Maxime Devos
2021-02-06 21:28                 ` Ludovic Courtès
2021-02-06 22:01                   ` Maxime Devos
2021-02-10 20:45                     ` Ludovic Courtès
2021-02-06 21:26               ` Ludovic Courtès
2021-02-14 12:29                 ` TOCTTOU race (was: Potential security weakness in Guix services) Maxime Devos
2021-02-14 17:19                   ` Bengt Richter
2021-02-18 17:54                   ` TOCTTOU race Ludovic Courtès
2021-02-19 18:01                     ` Maxime Devos
2021-02-22  8:54                       ` Ludovic Courtès
2021-02-22 19:13                         ` Maxime Devos
2021-02-23 15:30                           ` Ludovic Courtès
2021-02-27  7:41                             ` Maxime Devos
2021-03-10 10:07                               ` Ludovic Courtès
2021-02-10 20:54             ` Potential security weakness in Guix services Christopher Lemmer Webber

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