linux-kernel - Re: [PATCH 2/4] fs: Remove FIRMWARE_PREALLOC_BUFFER from kernel_read

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Message-ID: <c2e4f5ae-0a2f-454e-6847-c413ca719abf@broadcom.com>
Date:   Tue, 7 Jul 2020 20:06:23 -0700
From:   Scott Branden <scott.branden@...adcom.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     James Morris <jmorris@...ei.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.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>,
        Hans de Goede <hdegoede@...hat.com>,
        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,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 2/4] fs: Remove FIRMWARE_PREALLOC_BUFFER from
 kernel_read_file() enums

Hi Kees,

Thanks for looking at my patch series to see how it relates.
I see what you're trying to accomplish in various areas of cleanup.
I'll comment as I go through your individual emails.
1 comment below.

On 2020-07-07 2:55 p.m., Kees Cook wrote:
> On Tue, Jul 07, 2020 at 09:42:02AM -0700, Scott Branden wrote:
>> On 2020-07-07 1:19 a.m., Kees Cook wrote:
>>> FIRMWARE_PREALLOC_BUFFER is a "how", not a "what", and confuses the LSMs
>>> that are interested in filtering between types of things. The "how"
>>> should be an internal detail made uninteresting to the LSMs.
>>>
>>> Fixes: a098ecd2fa7d ("firmware: support loading into a pre-allocated buffer")
>>> Fixes: fd90bc559bfb ("ima: based on policy verify firmware signatures (pre-allocated buffer)")
>>> Fixes: 4f0496d8ffa3 ("ima: based on policy warn about loading firmware (pre-allocated buffer)")
>>> [...]
>>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>>> index 3f881a892ea7..95fc775ed937 100644
>>> --- a/include/linux/fs.h
>>> +++ b/include/linux/fs.h
>>> @@ -2993,10 +2993,10 @@ static inline void i_readcount_inc(struct inode *inode)
>>>    #endif
>>>    extern int do_pipe_flags(int *, int);
>>> +/* This is a list of *what* is being read, not *how*. */
>>>    #define __kernel_read_file_id(id) \
>>>    	id(UNKNOWN, unknown)		\
>>>    	id(FIRMWARE, firmware)		\
>> With this change, I'm trying to figure out how the partial firmware read is
>> going to work on top of this reachitecture.
>> Is it going to be ok to add READING_PARTIAL_FIRMWARE here as that is a
>> "what"?
> No, that's why I said you need to do the implementation within the API
> and not expect each LSM to implement their own (as I mentioned both
> times):
>
> https://lore.kernel.org/lkml/202005221551.5CA1372@keescook/
> https://lore.kernel.org/lkml/202007061950.F6B3D9E6A@keescook/
>
> I will reply in the thread above.
>
>>> -	id(FIRMWARE_PREALLOC_BUFFER, firmware)	\
>> My patch series gets rejected any time I make a change to the
>> kernel_read_file* region in linux/fs.h.
>> The requirement is for this api to move to another header file outside of
>> linux/fs.h
>> It seems the same should apply to your change.
> Well I'm hardly making the same level of changes, but yeah, sure, if
> that helps move things along, I can include that here.
>
>> Could you please add the following patch to the start of you patch series to
>> move the kernel_read_file* to its own include file?
>> https://patchwork.kernel.org/patch/11647063/
> https://lore.kernel.org/lkml/20200706232309.12010-2-scott.branden@broadcom.com/
>
> You've included it in include/linux/security.h and that should be pretty
> comprehensive, it shouldn't be needed in so many .c files.
Some people want the header files included in each c file they are used.
Others want header files not included if they are included in another 
header file.
I chose the first approach: every file that uses the api includes the 
header file.
I didn't know there was a standard approach to only put it in security.h
>