From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY_PATH)
Date: Sun, 25 Aug 2013 15:23:07 +0100
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Willy Tarreau <w@1wt.eu>,
	"security@kernel.org" <security@kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
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	Oleg Nesterov <oleg@redhat.com>,
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To: Andy Lutomirski <luto@amacapital.net>
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On Sun, Aug 25, 2013 at 12:26:34AM -0700, Andy Lutomirski wrote:

> I think this is more screwed up than just flink and open.  For example:
> 
> $ echo 'WTF' >test
> $ truncate -s 1 /proc/self/fd/3 3<test
> $ cat test
> W$
> 
> IMO that should have failed.

Why?  truncate() always follows links, so what's the problem with that
one?  That you get checks of truncate() and not ftruncate()?

> In an ideal world (I think) ffrob(N), frobat(N, "", AT_EMPTY_PATH),
> and frobat(AT_FDCWD, "/proc/self/fd/N) should generally do the same
> thing.

What about the cases where frob() and ffrob() check for different things?