linux-kernel - Re: [PATCH v4 0/3] initramfs: add support for xattrs in the initial ram disk

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Message-ID: <0c17bf9e-9b0b-b067-cf18-24516315b682@huawei.com>
Date:   Wed, 24 Jul 2019 17:34:53 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Rob Landley <rob@...dley.net>, <hpa@...or.com>,
        Arvind Sankar <nivedita@...m.mit.edu>
CC:     Mimi Zohar <zohar@...ux.ibm.com>, <viro@...iv.linux.org.uk>,
        <linux-security-module@...r.kernel.org>,
        <linux-integrity@...r.kernel.org>, <initramfs@...r.kernel.org>,
        <linux-api@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bug-cpio@....org>,
        <zohar@...ux.vnet.ibm.com>, <silviu.vlasceanu@...wei.com>,
        <dmitry.kasatkin@...wei.com>, <takondra@...co.com>,
        <kamensky@...co.com>, <arnd@...db.de>, <james.w.mcmechan@...il.com>
Subject: Re: [PATCH v4 0/3] initramfs: add support for xattrs in the initial
 ram disk

Is there anything I didn't address in this patch set, that is delaying
the review? I would appreciate if you can give me a feedback, positive
or negative.

Thanks a lot!

Roberto


On 7/15/2019 6:54 PM, Roberto Sassu wrote:
> Rob, Peter, Arvind, did you have the chance to have a look at this
> version of the patch set?
> 
> Thanks
> 
> Roberto
> 
> 
> On 7/1/2019 4:31 PM, Mimi Zohar wrote:
>> On Mon, 2019-07-01 at 16:42 +0300, Roberto Sassu wrote:
>>> On 6/30/2019 6:39 PM, Mimi Zohar wrote:
>>>> On Wed, 2019-06-26 at 10:15 +0200, Roberto Sassu wrote:
>>>>> On 6/3/2019 8:32 PM, Rob Landley wrote:
>>>>>> On 6/3/19 4:31 AM, Roberto Sassu wrote:
>>>>>>>> This patch set aims at solving the following use case: appraise 
>>>>>>>> files from
>>>>>>>> the initial ram disk. To do that, IMA checks the signature/hash 
>>>>>>>> from the
>>>>>>>> security.ima xattr. Unfortunately, this use case cannot be 
>>>>>>>> implemented
>>>>>>>> currently, as the CPIO format does not support xattrs.
>>>>>>>>
>>>>>>>> This proposal consists in including file metadata as additional 
>>>>>>>> files named
>>>>>>>> METADATA!!!, for each file added to the ram disk. The CPIO 
>>>>>>>> parser in the
>>>>>>>> kernel recognizes these special files from the file name, and 
>>>>>>>> calls the
>>>>>>>> appropriate parser to add metadata to the previously extracted 
>>>>>>>> file. It has
>>>>>>>> been proposed to use bit 17:16 of the file mode as a way to 
>>>>>>>> recognize files
>>>>>>>> with metadata, but both the kernel and the cpio tool declare the 
>>>>>>>> file mode
>>>>>>>> as unsigned short.
>>>>>>>
>>>>>>> Any opinion on this patch set?
>>>>>>>
>>>>>>> Thanks
>>>>>>>
>>>>>>> Roberto
>>>>>>
>>>>>> Sorry, I've had the window open since you posted it but haven't 
>>>>>> gotten around to
>>>>>> it. I'll try to build it later today.
>>>>>>
>>>>>> It does look interesting, and I have no objections to the basic 
>>>>>> approach. I
>>>>>> should be able to add support to toybox cpio over a weekend once 
>>>>>> I've got the
>>>>>> kernel doing it to test against.
>>>>>
>>>>> Ok.
>>>>>
>>>>> Let me give some instructions so that people can test this patch set.
>>>>>
>>>>> To add xattrs to the ram disk embedded in the kernel it is sufficient
>>>>> to set CONFIG_INITRAMFS_FILE_METADATA="xattr" and
>>>>> CONFIG_INITRAMFS_SOURCE="<file with xattr>" in the kernel 
>>>>> configuration.
>>>>>
>>>>> To add xattrs to the external ram disk, it is necessary to patch cpio:
>>>>>
>>>>> https://github.com/euleros/cpio/commit/531cabc88e9ecdc3231fad6e4856869baa9a91ef 
>>>>>
>>>>> (xattr-v1 branch)
>>>>>
>>>>> and dracut:
>>>>>
>>>>> https://github.com/euleros/dracut/commit/a2dee56ea80495c2c1871bc73186f7b00dc8bf3b 
>>>>>
>>>>> (digest-lists branch)
>>>>>
>>>>> The same modification can be done for mkinitramfs (add '-e xattr' 
>>>>> to the
>>>>> cpio command line).
>>>>>
>>>>> To simplify the test, it would be sufficient to replace only the cpio
>>>>> binary and the dracut script with the modified versions. For 
>>>>> dracut, the
>>>>> patch should be applied to the local dracut (after it has been renamed
>>>>> to dracut.sh).
>>>>>
>>>>> Then, run:
>>>>>
>>>>> dracut -e xattr -I <file with xattr> (add -f to overwrite the ram 
>>>>> disk)
>>>>>
>>>>> Xattrs can be seen by stopping the boot process for example by adding
>>>>> rd.break to the kernel command line.
>>>>
>>>> A simple way of testing, without needing any changes other than the
>>>> kernel patches, is to save the dracut temporary directory by supplying
>>>> "--keep" on the dracut command line, calling
>>>> usr/gen_initramfs_list.sh, followed by usr/gen_init_cpio with the "-e
>>>> xattr" option.
>>>
>>> Alternatively, follow the instructions to create the embedded ram disk
>>> with xattrs, and use the existing external ram disk created with dracut
>>> to check if xattrs are created.
>>
>> True, but this alternative is for those who normally use dracut to
>> create an initramfs, but don't want to update cpio or dracut.
>>
>> Mimi
>>
> 

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