Date: 19 Dec 2007 20:33:55 -0500
Message-ID: <20071220013355.3900.qmail@science.horizon.com>
From: linux@horizon.com
To: linux-kernel@vger.kernel.org, lkml@rtr.ca
Subject: Re: RFC: permit link(2)  to work across --bind mounts ?
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 975
Lines: 24

> Why does link(2) not support hard-linking across bind mount points
> of the same underlying filesystem ?

Whenever we get mount -r --bind working properly (which I use to place
copies of necessary shared libraries inside chroot jails while allowing
page cache sharing), this feature would break security.

mkdir /usr/lib/libs.jail
for i in $LIST_OF_LIBRARIES; do
	ln /usr/lib/$i /usr/lib/libs.jail/$i
done
mount -r /usr/lib/libs.jail /jail/lib
chown prisoner /usr/log/jail
mount /usr/log/jail /jail/usr/log
chrootuid /jail prisoner /bin/untrusted &

Although protections should be enough, but I'd rather avoid having the
prisoner link /jail/lib/libfoo.so (write returns EROFS) to /jail/usr/log
where it's potentially writeable.
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