RE: [OT] How to extract a BOM archive correctly?
RE: [OT] How to extract a BOM archive correctly?
- Subject: RE: [OT] How to extract a BOM archive correctly?
- From: "Karan, Cem (Civ, ARL/CISD)" <email@hidden>
- Date: Thu, 11 Oct 2007 07:18:09 -0400
- Thread-topic: [OT] How to extract a BOM archive correctly?
Are you sure they don't have any checksums? If I were designing a
system that was intended to change the permissions on things like system
files, I'd put in some kind of checksum code in there, just to make sure
that I was modifying the correct file. That wouldn't stop crackers
(they could just change the BOM), but it would be a nice sanity check to
make sure I really did have the right file.
Well, I guess you're right though. In the end, the only thing I can do
is experiment and see. If I really decide to go with a BOM parser, I'll
just have to write the code to be paranoid about possible changes to the
BOM archives.
Hmmm... actually, I just realized that I can sidestep the problem fairly
neatly by parsing the output of lsbom once, storing all the information
I'm interested in in my own Core Data datastore, and modifying all the
permissions there. Running a custom program similar to Disk Utility
after Disk Utility is run will fix all the permissions problems caused
by bad BOMs. And I can compare permissions between my data store and
any updated BOMs fairly easily that way... you've just given me
something to think about and chew on for a while... Thanks!
Thanks,
Cem Karan
-----Original Message-----
From: Eduard de Jong [mailto:email@hidden]
Sent: Wednesday, October 10, 2007 5:24 PM
To: Karan, Cem (Civ, ARL/CISD)
Cc: Xcode Users
Subject: RE: [OT] How to extract a BOM archive correctly?
A BOM is not an archive, checksums is what archives do. Reading man
ditto tells me that a bom can be used to selectively retrieve files from
an archive. This strongly suggests it contains only a list of file
names. If it contains any thing else it would be per file info that the
archive it self would not store...
Maybe you can experiment...
cheers,
At 06:54 -0400 09-10-2007, Karan, Cem (Civ, ARL/CISD) wrote:
>Can you point me to where you read this? Finlay Dobbie suggested
>something similar to me earlier, but my concern was that there would be
>file checksums, etc. stored in there. Are you sure that only what you
>have down below is actually put into a BOM archive?
>
>Thanks,
>Cem Karan
>
>-----Original Message-----
>From: Eduard de Jong [mailto:email@hidden]
>Sent: Saturday, October 06, 2007 5:50 PM
>To: Karan, Cem (Civ, ARL/CISD)
>Cc: Xcode Users
>Subject: Re: [OT] How to extract a BOM archive correctly?
>
>You are right, the man pages are very thin on actual data on the format
>of the file.
>
>The way to make a bom file, which they suggest is to create a directory
>structure with all names, owner id, group id and acsess bits set and
>then feed that into mkbom. As i understand it, none of these files need
>to be present with actual data to make a bom.
>
>One aproach could be to use a shell script to parse the output of lsbom
>to reconstruct the file system is specifies with empty files, apply
>your modifications to the result and then get a modified bom with
mkbom.
>
>
>At 01:54 +0100 06-10-2007, Finlay Dobbie wrote:
>>On 05/10/2007, Karan, Cem (Civ, ARL/CISD) <email@hidden> wrote:
>>> I've read the man pages before, but they aren't specifications;
>>> that
>
>>> is, if I write a tool that is designed to parse a BOM file, I need
>>> to know what the different bytes are that it sees. I can reverse
>>> engineer this, but that can lead to errors that I would prefer to
>>> avoid. The man pages for bom, lsbom, and mkbom (at least on my
>>> machine, a fairly stock 10.4.10 machine) don't give enough
>>> information on this for me to write a tool. Basically, I'm looking
>>> for a spec like you'd find if you were trying to create a new jpeg
>>> library; you need more than what help files for your favorite jpeg
>>> viewer provide. In the same way, I need more than what the
>>> man/info
>pages provide.
>>
>>There is no such specification, it is a private file format. You could
>>always just parse the output of lsbom, which will give you what you
>>need.
>>
>> -- Finlay
>
>
>--
>Eduard
> "E por se movo"
--
Eduard
"E por se movo"
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