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Subject: Re: [PATCH v3 2/2] initramfs: introduce do_readxattrs()
To:     Arvind Sankar <nivedita@alum.mit.edu>
Cc:     Roberto Sassu <roberto.sassu@huawei.com>, viro@zeniv.linux.org.uk,
        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, zohar@linux.vnet.ibm.com,
        silviu.vlasceanu@huawei.com, dmitry.kasatkin@huawei.com,
        takondra@cisco.com, kamensky@cisco.com, arnd@arndb.de,
        rob@landley.net, james.w.mcmechan@gmail.com, niveditas98@gmail.com
References: <20190517165519.11507-1-roberto.sassu@huawei.com>
 <20190517165519.11507-3-roberto.sassu@huawei.com>
 <CD9A4F89-7CA5-4329-A06A-F8DEB87905A5@zytor.com>
 <20190517210219.GA5998@rani.riverdale.lan>
From:   "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <d48f35a1-aab1-2f20-2e91-5e81a84b107f@zytor.com>
Date:   Fri, 17 May 2019 14:47:31 -0700
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On 5/17/19 2:02 PM, Arvind Sankar wrote:
> On Fri, May 17, 2019 at 01:18:11PM -0700, hpa@zytor.com wrote:
>>
>> Ok... I just realized this does not work for a modular initramfs, composed at load time from multiple files, which is a very real problem. Should be easy enough to deal with: instead of one large file, use one companion file per source file, perhaps something like filename..xattrs (suggesting double dots to make it less likely to conflict with a "real" file.) No leading dot, as it makes it more likely that archivers will sort them before the file proper.
> This version of the patch was changed from the previous one exactly to deal with this case --
> it allows for the bootloader to load multiple initramfs archives, each
> with its own .xattr-list file, and to have that work properly.
> Could you elaborate on the issue that you see?
> 

Well, for one thing, how do you define "cpio archive", each with its own
.xattr-list file? Second, that would seem to depend on the ordering, no,
in which case you depend critically on .xattr-list file following the
files, which most archivers won't do.

Either way it seems cleaner to have this per file; especially if/as it
can be done without actually mucking up the format.

I need to run, but I'll post a more detailed explanation of what I did
in a little bit.

	-hpa