linux-kernel - Re: symlinks with permissions

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Message-ID: <20091031023010.GB17680@shareable.org>
Date:	Sat, 31 Oct 2009 02:30:10 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Pavel Machek <pavel@....cz>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	Jan Kara <jack@...e.cz>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk
Subject: Re: symlinks with permissions

Eric W. Biederman wrote:
> Pavel Machek <pavel@....cz> writes:
> >> How many linux shell scripts and other applications that use /dev/fd/N
> >> or /proc/self/fd/N will you be breaking?
> >
> > Zero. (Well unless someone is exploiting it in wild).
> 
> There are other differences like different offsets etc that may matter.
> 
> >> Closing a theoretical security hole at the expense of breaking real
> >> applications is a show stopper.
> >
> > I don't plan to remove /proc/*/fd; but I would like it to behave like
> > dup().
> >
> > (I still hope some security team does work for me :-).

Yes, it must not be like dup(), sharing the file pointer, because I'm
sure that really will break some programs.

Like all the ones using gnulib (formerly libiberty) which use
/proc/self/fd/N/path/to/file to implement fake openat(N,"path/to/file").

> I bet you will get a lot more traction and discussion if you write
> a basic mostly working version of the patch.

I agree, and I'll be happy to review/break it ;-)

-- Jamie
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