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From: Matthew Dillon <dillon@apollo.backplane.com>
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To: Tim Kientzle <kientzle@freebsd.org>
References: <20040813235434.GA75875@xor.obsecurity.org>
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cc: current@freebsd.org
cc: Kris Kennaway <kris@obsecurity.org>
Subject: Re: bsdtar's security restrictions (was Re: Spurious EACCES
	errorsfrom apache)
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: > This is bad when some of those directories
:> already exist, because other processes trying to access files in the
:> directory hierarchy may lose the race and fail.
:
:<scratching head>  I don't think I understand what
:exactly you're trying to do.
:
:You are extracting archives over an existing directory
:that is currently being served by an Apache process in
:order to refresh some (presumably) small number of files?
:
:Give me some more details about your situation and I'll
:see what I can come up with.
:
:Tim

    Using tar for that sort of thing is a bad idea anyway, since tar (and
    bsdtar) do not use the create-temporary/write/rename trick to atomically
    replace files.  This means that a live server like a web server could
    easily 'catch' files in the middle of being written, leading to odd 
    errors.

    A far better way to handle updates is to extract to a temporary directory
    and then use something like 'cpdup -o' (/usr/ports/sysutils/cpdup),
    which does properly use the rename trick, to update the live master.
    Or, alternatively, NFS mount the master and use cpdup to update each
    slave (being sure to synchronize against the master so you don't catch
    the master in the middle of an update).

					-Matt
					Matthew Dillon 
					<dillon@backplane.com>