linux-kernel - Re: *at syscalls for xattrs?

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Message-ID: <469BB190.1080300@zytor.com>
Date:	Mon, 16 Jul 2007 10:57:36 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	Miklos Szeredi <miklos@...redi.hu>, jeremy@...p.org,
	jengelh@...putergmbh.de, viro@....linux.org.uk, nmiell@...cast.net,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: *at syscalls for xattrs?

Jeff Garzik wrote:
>>
>> What the *at() interfaces really do is fix/paper over a longstanding
>> wart in Unix: the cwd really should have been a standard file descriptor
>> (like stdin/stdout/stderr) instead of a magic piece of state maintained
>> in kernel space.
> 
> It's more than a wart, IMO.  *at() allows one to close races (with
> potential security implications) that are otherwise impossible to close,
> in directory traversal.
> 
> *at() permits a userspace program to hold proper references to all
> objects during a directory traversal, with all that implies.
> 

Well, as Jeremy pointed out, in the absence of threads you can do the
same thing with fchdir(), however, that's much more of a hack.

	-hpa
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