linux-kernel - Re: [RFC PATCH 2/2] integrity: double check iint

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Message-ID: <f370fed01e9d341ae6e4265785ad85b83dbc889c.camel@linux.ibm.com>
Date:   Wed, 24 Mar 2021 08:17:10 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        linux-integrity@...r.kernel.org, James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Eric Biggers <ebiggers@...nel.org>
Subject: Re: [RFC PATCH 2/2] integrity: double check iint_cache was
 initialized

On Wed, 2021-03-24 at 12:58 +0100, Dmitry Vyukov wrote:
> On Wed, Mar 24, 2021 at 12:49 PM Mimi Zohar <zohar@...ux.ibm.com> wrote:
> >
> > On Wed, 2021-03-24 at 12:37 +0100, Dmitry Vyukov wrote:
> > > On Wed, Mar 24, 2021 at 12:21 PM Tetsuo Handa
> > > <penguin-kernel@...ove.sakura.ne.jp> wrote:
> > > >
> > > > On 2021/03/24 20:10, Mimi Zohar wrote:
> > > > > On Wed, 2021-03-24 at 19:10 +0900, Tetsuo Handa wrote:
> > > > >> On 2021/03/24 1:13, Mimi Zohar wrote:
> > > > >>> On Wed, 2021-03-24 at 00:14 +0900, Tetsuo Handa wrote:
> > > > >>>> On 2021/03/23 23:47, Mimi Zohar wrote:
> > > > >>>>> Initially I also questioned making "integrity" an LSM.  Perhaps it's
> > > > >>>>> time to reconsider.   For now, it makes sense to just fix the NULL
> > > > >>>>> pointer dereferencing.
> > > > >>>>
> > > > >>>> Do we think calling panic() as "fix the NULL pointer dereferencing" ?
> > > > >>>
> > > > >>> Not supplying "integrity" as an "lsm=" option is a user error.  There
> > > > >>> are only two options - allow or deny the caller to proceed.   If the
> > > > >>> user is expecting the integrity subsystem to be properly working,
> > > > >>> returning a NULL and allowing the system to boot (RFC patch version)
> > > > >>> does not make sense.   Better to fail early.
> > > > >>
> > > > >> What does the "user" mean? Those who load the vmlinux?
> > > > >> Only the "root" user (so called administrators)?
> > > > >> Any users including other than "root" user?
> > > > >>
> > > > >> If the user means those who load the vmlinux, that user is explicitly asking
> > > > >> for disabling "integrity" for some reason. In that case, it is a bug if
> > > > >> booting with "integrity" disabled is impossible.
> > > > >>
> > > > >> If the user means something other than those who load the vmlinux,
> > > > >> is there a possibility that that user (especially non "root" users) is
> > > > >> allowed to try to use "integrity" ? If processes other than global init
> > > > >> process can try to use "integrity", wouldn't it be a DoS attack vector?
> > > > >> Please explain in the descripotion why calling panic() does not cause
> > > > >> DoS attack vector.
> > > > >
> > > > > User in this case, is anyone rebooting the system and is intentionally
> > > > > changing the default values, dropping the "integrity" option on the
> > > > > boot command line.
> > > >
> > > > OK. Then, I expect that the system boots instead of calling panic().
> > > > That user is explicitly asking for disabling "integrity" for some reason.
> > >
> > > That was actually my intention. The prebuilt kernel that I use for
> > > things has all LSMs enabled, but then I needed to try some workload
> > > with only 1 specific LSM, so I gave a different lsm= argument.
> >
> > IMA/EVM is dependent on "integrity".  Was your intention to also
> > disable IMA and EVM?
> 
> I think, yes... or not sure. I was trying to test a bug that requires
> a different major LSM and all minor LSMs are presumably irrelevant. I
> dropped existing lsm= arg and added something like lsm=apparmor.
> 
> > If so, when disabling "integrity", don't load an
> > IMA policy.
> 
> I don't really know what this means. I guess it simply comes from the
> image? If so, there was no easy way to avoid loading.

There are a couple of builtin IMA policies, which may be loaded on boot
by specifying on the boot command line "ima_policy=".   Unless the boot
command line "ima_policy=" option is specified, no policy will loaded.

A custom IMA policy may subsequently be loaded, normally in the
initramfs, by echo'ing the file pathname to
/sys/kernel/security/ima/policy.

Mimi