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

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Message-ID: <0a0c5cc5-0e1b-ef01-60c4-5247af2124f4@i-love.sakura.ne.jp>
Date:   Wed, 24 Mar 2021 19:10:19 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     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>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH 2/2] integrity: double check iint_cache was
 initialized

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.