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

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Date:   Mon, 15 Jul 2019 18:54:12 +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

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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