Re: [PATCH v2 3/3] security: Add LSMs dependencies to CONFIG_LSM

[Masahiro Yamada]

On Tue, Feb 16, 2021 at 4:03 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
>
> On Mon, Feb 15, 2021 at 7:17 PM Mickaël Salaün <mic@xxxxxxxxxxx> wrote:
> > From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
> >
> > Thanks to the previous commit, this gives the opportunity to users, when
> > running make oldconfig, to update the list of enabled LSMs at boot time
> > if an LSM has just been enabled or disabled in the build.  Moreover,
> > this list only makes sense if at least one LSM is enabled.
> >
> > Cc: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> > Cc: James Morris <jmorris@xxxxxxxxx>
> > Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> > Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20210215181511.2840674-4-mic@xxxxxxxxxxx
> > ---
> >
> > Changes since v1:
> > * Add CONFIG_SECURITY as a dependency of CONFIG_LSM.  This prevent an
> >   error when building without any LSMs.
> > ---
> >  security/Kconfig | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/security/Kconfig b/security/Kconfig
> > index 7561f6f99f1d..addcc1c04701 100644
> > --- a/security/Kconfig
> > +++ b/security/Kconfig
> > @@ -277,6 +277,10 @@ endchoice
> >
> >  config LSM
> >         string "Ordered list of enabled LSMs"
> > +       depends on SECURITY || SECURITY_LOCKDOWN_LSM || SECURITY_YAMA || \
> > +               SECURITY_LOADPIN || SECURITY_SAFESETID || INTEGRITY || \
> > +               SECURITY_SELINUX || SECURITY_SMACK || SECURITY_TOMOYO || \
> > +               SECURITY_APPARMOR || BPF_LSM
>
> This looks really awkward, since all of these already depend on
> SECURITY (if not, it's a bug)... I guarantee you that after some time
> someone will come, see that the weird boolean expression is equivalent
> to just SECURITY, and simplify it.


Currently, LSM does not depend on SECURITY.
So you can always define LSM irrespective of SECURITY,
which seems a bug.

So, I agree with adding 'depends on SECURITY'.

What he is trying to achieve in this series
seems wrong, of course.










> I assume the new mechanism wouldn't work as intended if there is just
> SECURITY? If not, then maybe you should rather specify this value
> dependency via some new  field rather than abusing "depends on" (say,
> "value depends on"?). The fact that a seemingly innocent change to the
> config definition breaks your mechanism suggests that the design is
> flawed.
>
> I do think this would be a useful feature, but IMHO shouldn't be
> implemented like this.
>
> >         default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
> >         default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
> >         default "lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
> > --
> > 2.30.0
> >
>
> --
> Ondrej Mosnacek
> Software Engineer, Linux Security - SELinux kernel
> Red Hat, Inc.
>


-- 
Best Regards
Masahiro Yamada