linux-kernel - Re: [PATCH v2 0/3] initramfs: add support for xattrs in the initial ram disk

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Message-ID: <bf0d02fc-d6ce-ef1d-bb7d-7ca14432c6fd@huawei.com>
Date:   Fri, 10 May 2019 08:56:18 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Rob Landley <rob@...dley.net>, <viro@...iv.linux.org.uk>
CC:     <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>, <zohar@...ux.vnet.ibm.com>,
        <silviu.vlasceanu@...wei.com>, <dmitry.kasatkin@...wei.com>,
        <takondra@...co.com>, <kamensky@...co.com>, <hpa@...or.com>,
        <arnd@...db.de>, <james.w.mcmechan@...il.com>
Subject: Re: [PATCH v2 0/3] initramfs: add support for xattrs in the initial
 ram disk

On 5/9/2019 8:34 PM, Rob Landley wrote:
> On 5/9/19 6:24 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 marshaling pathnames and xattrs in a file called
>> .xattr-list. They are unmarshaled by the CPIO parser after all files have
>> been extracted.
> 
> So it's in-band signalling that has a higher peak memory requirement.

This can be modified. Now I allocate the memory necessary for the path
and all xattrs of a file (max: .xattr-list size - 10 bytes). I could
process each xattr individually (max: 255 + 1 + 65536 bytes).


>> The difference with another proposal
>> (https://lore.kernel.org/patchwork/cover/888071/) is that xattrs can be
>> included in an image without changing the image format, as opposed to
>> defining a new one. As seen from the discussion, if a new format has to be
>> defined, it should fix the issues of the existing format, which requires
>> more time.
> 
> So you've explicitly chosen _not_ to address Y2038 while you're there.

Can you be more specific?

Thanks

Roberto


> Rob
> 

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