From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: Connecting to sockets on MNT_READONLY mounts? Date: Fri, 2 May 2014 00:51:35 +0100 Message-ID: <20140501235135.GE18016@ZenIV.linux.org.uk> References: <20140501223432.GD18016@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Linux FS Devel , "linux-kernel@vger.kernel.org" , Network Development To: Andy Lutomirski Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, May 01, 2014 at 04:00:49PM -0700, Andy Lutomirski wrote: > On Thu, May 1, 2014 at 3:34 PM, Al Viro wrote: > > On Thu, May 01, 2014 at 03:20:00PM -0700, Andy Lutomirski wrote: > >> Is it supposed to work? > > > > Why the hell not? Same as opening a device node on r/o filesystem for > > write, or doing the same with FIFO. > > You can't bind a socket on a read-only fs, so I thought it was a fair question. > > I'll write a patch to add MS_NOIPCCONNECT and MNT_NOIPCCONNECT to > block connect on unix sockets and open on fifos. This will be useful > for sandboxes that want to prevent sandboxed programs from accessing > undesirable parts of the outside world. Sigh... Don't expose those FIFOs et.al. to them, then. mount --bind /dev/null as part of setting the sucker up. And if you *are* blindly exposing the host filesystems to them wholesale, sockets and fifos are the least of your problems, even if you do that read-only.