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

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Date:   Wed, 24 Mar 2021 12:37:18 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>, 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, 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.