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

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Message-ID: <05ca20d0-9596-152e-4da2-1ffe28c52055@i-love.sakura.ne.jp>
Date:   Wed, 24 Mar 2021 20:20:39 +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 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.