linux-kernel - Re: [PATCH v2] initramfs: print error and shell out for unsupported content

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Message-ID: <532CC625.7020509@ahsoftware.de>
Date:	Sat, 22 Mar 2014 00:07:17 +0100
From:	Alexander Holler <holler@...oftware.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] initramfs: print error and shell out for unsupported
 content

Am 21.03.2014 23:55, schrieb Andrew Morton:
> On Fri, 21 Mar 2014 23:49:57 +0100 Alexander Holler <holler@...oftware.de> wrote:
> 
>> Am 21.03.2014 22:03, schrieb Andrew Morton:
>>> On Thu, 20 Mar 2014 23:00:45 +0100 Alexander Holler <holler@...oftware.de> wrote:
>>>
>>>> The initramfs generation is broken for file and directory names which contain
>>>> colons or spaces. Print an error and don't try to continue.
>>
>>> It would be better to fix the it-doesnt-work-with-all-filenames bug. 
>>> Any details on that?
>>
>> IMHO not worth the time. The whole process which is curently used is
>> extremly fragile.
>>
>> E.g it's almost guaranteed to fail trying to include arbitrary filenames
>> as dependencies in a Makefile. Besides the one problem I've discoverd
>> with colons, there could be much more things happen, e.g. with filenames
>> which do include other special Makefile characters you all would have to
>> escape correctly.
>>
>> And the problem with spaces isn't as easy to fix as it first does look
>> like. I think it might be easier to write the whole stuff new instead of
>> trying to escape the spaces in various ways needed to end up correctly
>> in the cpio (it first goes through shell code and is then feeded as some
>> list to a C program).
>>
>> And I think that just isn't worth the time. Using find | cpio works just
>> fine to generate a cpio archive and usually an initramfs just contains
>> some megabytes. So it isn't a problem at all to rebuild the complete
>> cpio archive with every call of make, it doesn't need much more than
>> about a second or similiar on almost any machine.
>>
>> And for the records, I indeed had a deeper look, trying to fix it. But,
>> as said, quickly realized that it will need too much effort and doesn't
>> make sense, if it will be doable correctly at all.
>>
> 
> huh, OK.
> 
> Should we check for \t and \n as well?

Hmm, maybe. But usually there aren't filenames wich do contain those
characters, and if you want to break (or exploit) the kernel build
process, there are easier ways. But colons and spaces are more widely
used, e.g. the colons in my initramfs were generated by bluez (look at
/var/lib/bluetooth).

I think the current process is good enough for most stuff one wants to
put into an initramfs, and it has the great feature of the uid/guid
translation.
So just a quick check to avoid the most basic problems should be ok. And
I don't really see a need to check for \t and \n too, because nobody
sane uses them in filenames. But ok, that just would be a few chars more
in the regex for find. ;)

I leave that up to you.

Regards,

Alexander Holler
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