[bug#47013] [PATCH] gnu: Harden filesystem links.

[Ludovic Courtès]

Hi,

Leo Famulari <leo@famulari.name> skribis:

> On Tue, Mar 16, 2021 at 08:54:52PM -0400, Leo Famulari wrote:
>> As a compromise, we could create a new variable %default-sysctl-settings
>> and add a sysctl-service-type in %base-services that uses that variable.
>
> Here is a v4 patch that implements this. I wasn't sure where to put
> %default-sysctl-settings, so it's in (gnu services sysctl).
>
> From my naive perspective, it seemed to me that it belongs in (gnu
> system), but when I exported it from there, and imported (gnu system) in
> (gnu services base), building Guix crashes like this:
>
> ------
> [ 12%] LOAD     guix/scripts/system.scm
> ice-9/eval.scm:293:34: error: %default-sysctl-settings: unbound variable
> hint: Did you forget `(use-modules (gnu system))'?

Yeah, some circular module dependency.

I propose this minor change:

> +++ b/gnu/services/base.scm
> @@ -35,6 +35,7 @@
>    #:use-module (gnu services)
>    #:use-module (gnu services admin)
>    #:use-module (gnu services shepherd)
> +  #:use-module (gnu services sysctl)
>    #:use-module (gnu system pam)
>    #:use-module (gnu system shadow)                ; 'user-account', etc.
>    #:use-module (gnu system uuid)
> @@ -2532,6 +2533,10 @@ to handle."
>                   (udev-configuration
>                     (rules (list lvm2 fuse alsa-utils crda))))
>  
> +        (service sysctl-service-type
> +                 (sysctl-configuration
> +                   (settings %default-sysctl-settings)))

Write (service sysctl-service-type) here, and…

> +++ b/gnu/services/sysctl.scm
> @@ -25,7 +25,8 @@
>    #:use-module (srfi srfi-1)
>    #:use-module (ice-9 match)
>    #:export (sysctl-configuration
> -            sysctl-service-type))
> +            sysctl-service-type
> +            %default-sysctl-settings))
>  
>
>  ;;;
> @@ -74,3 +75,8 @@
>                (settings (append (sysctl-configuration-settings config)
>                                  settings)))))
>     (default-value (sysctl-configuration))))
> +
> +(define %default-sysctl-settings
> +  ;; Default kernel parameters enabled with sysctl.
> +  '(("fs.protected_hardlinks" . "1")
> +    ("fs.protected_symlinks" . "1")))

… change the default value of the ‘settings’ field of
<sysctl-configuration> to be ‘%default-sysctl-settings’.

We should also add a @defvr and adjust guix.texi accordingly.

WDYT?

Thanks,
Ludo’.