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Subject: Re: [PATCH v4 0/3] initramfs: add support for xattrs in the initial
 ram disk
To:     Mimi Zohar <zohar@linux.ibm.com>, Rob Landley <rob@landley.net>,
        <viro@zeniv.linux.org.uk>
CC:     <linux-security-module@vger.kernel.org>,
        <linux-integrity@vger.kernel.org>, <initramfs@vger.kernel.org>,
        <linux-api@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <bug-cpio@gnu.org>,
        <zohar@linux.vnet.ibm.com>, <silviu.vlasceanu@huawei.com>,
        <dmitry.kasatkin@huawei.com>, <takondra@cisco.com>,
        <kamensky@cisco.com>, <hpa@zytor.com>, <arnd@arndb.de>,
        <james.w.mcmechan@gmail.com>, <niveditas98@gmail.com>
References: <20190523121803.21638-1-roberto.sassu@huawei.com>
 <cf9d08ca-74c7-c945-5bf9-7c3495907d1e@huawei.com>
 <541e9ea1-024f-5c22-0b58-f8692e6c1eb1@landley.net>
 <33cfb804-6a17-39f0-92b7-01d54e9c452d@huawei.com>
 <1561909199.3985.33.camel@linux.ibm.com>
From:   Roberto Sassu <roberto.sassu@huawei.com>
Message-ID: <45164486-782f-a442-e442-6f56f9299c66@huawei.com>
Date:   Mon, 1 Jul 2019 16:42:13 +0300
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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.

Roberto

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