linux-kernel - Re: [PATCH] vfs: new O

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Message-ID: <20091004190304.GJ1378@ucw.cz>
Date:	Sun, 4 Oct 2009 21:03:04 +0200
From:	Pavel Machek <pavel@....cz>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Andreas Dilger <adilger@....com>, Valdis.Kletnieks@...edu,
	linux@...blig.org, agruen@...e.de, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: new O_NODE open flag

On Mon 2009-09-28 18:04:10, Miklos Szeredi wrote:
> On Mon, 28 Sep 2009, Andreas Dilger wrote:
> > On Sep 28, 2009  12:25 +0200, Miklos Szeredi wrote:
> > > BTW I just checked, and it is possible to re-open or promote an fd
> > > opened with O_NODE like this:
> > > 
> > > 	char tmp[64];
> > > 
> > > 	fd = open(filename, O_NODE | O_NOACCESS);
> > > 	/* ... */
> > > 	sprintf(tmp, "/proc/self/fd/%i", fd);
> > > 	fd_rw = open(tmp, O_RDWR);
> > > 
> > > Now fd_rw is guaranteed to refer to the same inode as fd.
> > 
> > It seems very unpleasant to require applications using O_NODE to
> > reopen files using /proc.
> 
> The point of the above example was that reopening a file descriptor
> with upgraded (or downgraded) access mode is even now possible.  Which
> either means:
> 
>  a) the current permission model under /proc/PID/fd has a security
>     hole (which Jamie is worried about)

I believe its bugtraq time. Being able to reopen file with additional
permissions looks like  a security problem...

Jamie, do you have some test script? And do you want your 15 minutes
 of bugtraq fame? ;-).
 
									Pavel

-- 
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