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SubjectRe: [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?



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:
>>>> (xattr-v1 branch)
>>>> and dracut:
>>>> (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
>>>> 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/, 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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