Subject: Re: symlinks with permissions
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Pavel Machek <pavel@ucw.cz>
Cc: Jan Kara <jack@suse.cz>, "J. Bruce Fields" <bfields@fieldses.org>,
       "Serge E. Hallyn" <serue@us.ibm.com>,
       kernel list <linux-kernel@vger.kernel.org>,
       linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
       jamie@shareable.org
In-Reply-To: <20091025093604.GA1501@ucw.cz>
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	 <20091025093604.GA1501@ucw.cz>
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Date: Mon, 26 Oct 2009 14:22:16 -0400
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On Sun, 2009-10-25 at 10:36 +0100, Pavel Machek wrote:
> Well, it is unexpected and mild security hole.
> 
> Part of the problem is that even  if you have read-only
> filedescriptor, you can upgrade it to read-write, even if path is
> inaccessible to you.
> 
> So if someone passes you read-only filedescriptor, you can still write
> to it.
> 									Pavel

If someone passes you a file descriptor, can't you in any case play
games with, openat(fd,"",O_RDWR), in order to achieve the same thing? I
must admit I haven't tried it yet, but at a first glance I can't see
anything that prevents me from doing this...

Cheers
  Trond

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