linux-kernel - Re: [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY

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Date:	Sun, 25 Aug 2013 15:23:07 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Willy Tarreau <w@....eu>,
	"security@...nel.org" <security@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Brad Spengler <spender@...ecurity.net>
Subject: Re: [PATCH v2] vfs: Tighten up linkat(..., AT_EMPTY_PATH)

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?
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