linux-kernel - Re: O_NOLINK for open()

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Message-ID: <46E85E41.5000403@zytor.com>
Date:	Wed, 12 Sep 2007 14:46:41 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Brent Casavant <bcasavan@....com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: O_NOLINK for open()

Brent Casavant wrote:
> On Wed, 12 Sep 2007, H. Peter Anvin wrote:
> 
>> Brent Casavant wrote:
> 
>>> 	http://marc.info/?l=linux-kernel&m=93032806224160&w=2
>> This link talks about file flags handling.  I don't see the relevance to
>> this problem at all.  However, this is a very long thread, so if there
>> is anything specific that you want to point to, then please elucidate.
> 
> Oops, my mistake -- I pasted the wrong URL.  I meant this thread, this
> post in particular:
> 
> 	http://marc.info/?l=linux-kernel&m=88937224115435&w=2
> 
> Still, O_NOLINK would seem to be a valuable addition, and greatly
> simplify secure temporary file creation.
> 

Avoiding -- or at least detecting -- symlink racing with mkdir() is
relatively simple: run mkdir(), make sure you don't get EEXIST or
something like that, lstat() the resulting path -- it should be a
directory with all the right modes and ownerships.

I believe -- but I'm not certain -- that mkdtemp() in glibc will do all
this for you.  If not, I would consider that a glibc bug.

	-hpa
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