linux-kernel - Re: [PATCH 0/4] Fix misused kernel_read

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Date:   Wed, 8 Jul 2020 13:58:47 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        James Morris <jmorris@...ei.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Scott Branden <scott.branden@...adcom.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jessica Yu <jeyu@...nel.org>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Matthew Garrett <matthewgarrett@...gle.com>,
        David Howells <dhowells@...hat.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        KP Singh <kpsingh@...gle.com>, Dave Olsthoorn <dave@...aar.me>,
        Peter Jones <pjones@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Boyd <stephen.boyd@...aro.org>,
        Paul Moore <paul@...l-moore.com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH 0/4] Fix misused kernel_read_file() enums

Hi,

On 7/8/20 1:55 PM, Luis Chamberlain wrote:
> On Wed, Jul 08, 2020 at 01:37:41PM +0200, Hans de Goede wrote:
>> Hi,
>>
>> On 7/8/20 1:01 PM, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 7/7/20 10:19 AM, Kees Cook wrote:
>>>> Hi,
>>>>
>>>> In looking for closely at the additions that got made to the
>>>> kernel_read_file() enums, I noticed that FIRMWARE_PREALLOC_BUFFER
>>>> and FIRMWARE_EFI_EMBEDDED were added, but they are not appropriate
>>>> *kinds* of files for the LSM to reason about. They are a "how" and
>>>> "where", respectively. Remove these improper aliases and refactor the
>>>> code to adapt to the changes.
>>>>
>>>> Additionally adds in missing calls to security_kernel_post_read_file()
>>>> in the platform firmware fallback path (to match the sysfs firmware
>>>> fallback path) and in module loading. I considered entirely removing
>>>> security_kernel_post_read_file() hook since it is technically unused,
>>>> but IMA probably wants to be able to measure EFI-stored firmware images,
>>>> so I wired it up and matched it for modules, in case anyone wants to
>>>> move the module signature checks out of the module core and into an LSM
>>>> to avoid the current layering violations.
>>>>
>>>> This touches several trees, and I suspect it would be best to go through
>>>> James's LSM tree.
>>>>
>>>> Thanks!
>>>
>>>
>>> I've done some quick tests on this series to make sure that
>>> the efi embedded-firmware support did not regress.
>>> That still works fine, so this series is;
>>>
>>> Tested-by: Hans de Goede <hdegoede@...hat.com>
>>
>> I made a mistake during testing I was not actually running the
>> kernel with the patches added.
>>
>> After fixing that I did find a problem, patch 4/4:
>> "module: Add hook for security_kernel_post_read_file()"
>>
>> Breaks module-loading for me. This is with the 4 patches
>> on top of 5.8.0-rc4, so this might just be because I'm
>> not using the right base.
>>
>> With patch 4/4 reverted things work fine for me.
>>
>> So, please only add my Tested-by to patches 1-3.
> 
> BTW is there any testing covered by the selftests for the firmware
> laoder which would have caputured this? If not can you extend
> it with something to capture this case you ran into?

This was not a firmware-loading issue. For me in my tests,
which were limited to 1 device, patch 4/4, which only touches
the module-loading code, stopped module loading from working.

Since my test device has / on an eMMC and the kernel config
I'm using has mmc-block as a module, things just hung in the
initrd since no modules could be loaded, so I did not debug
this any further. Dropping  patch 4/4 from my local tree
solved this.

Regards,

Hans