Date: Mon, 15 Jan 2007 22:08:26 +0100 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: Dirk Engling <erdgeist@erdgeist.org> Cc: freebsd-security@freebsd.org Subject: Re: HEADS UP: Re: FreeBSD Security Advisory FreeBSD-SA-07:01.jail Message-ID: <20070115210826.GA2839@garage.freebsd.pl> In-Reply-To: <45ABDC7C.6060407@erdgeist.org> References: <200701111841.l0BIfWOn015231@freefall.freebsd.org> <45A6DB76.40800@freebsd.org> <20070113112937.GI90718@garage.freebsd.pl> <45ABDC7C.6060407@erdgeist.org>
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On Mon, Jan 15, 2007 at 08:56:44PM +0100, Dirk Engling wrote:
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>=20
> Pawel Jakub Dawidek wrote:
>=20
> > I'll keep /var/log/console.log outside a jail, because using
> > 'realpath -c' will be dangerous once the jail is running. There could be
> > a race where `realpath -c` returns one path, an attacker inside a jail
> > changes one of resolved path's component and rc.d/jail from outside a
> > jail tries to use it.
>=20
> A simple way to prevent race conditions (here an example to mount devfs
> into jails) is:
>=20
> cd ${jail_root}
> j_root=3D`pwd`
> cd ${jail_dev_dir}
> j_dev=3D`pwd`
> eval evil_doer=3D\$\{j_dev#${j_root}\}
> [ "$evil_doer" =3D "$j_dev" ] && exit
> mount_devfs devfs .
# ls -l /jails
lrwxr-x--- 1 root wheel 9 15 sty 21:58 /jails -> usr/jails
# jail_root=3D"/usr/jails"
# jail_dev_dir=3D"/jails/dev"
# cd ${jail_root}
# j_root=3D`pwd`
# echo $j_root
/usr/jails
# cd ${jail_dev_dir}
# j_dev=3D`pwd`
# echo $j_dev
/jails/dev
# eval evil_doer=3D\$\{j_dev#${j_root}\}
# echo $evil_doer
/jails/dev
# [ "$evil_doer" =3D "$j_dev" ] && echo "false positive"
false positive
In other words, it may break existing configurations.
> To do the same with console.log (I _really_ like this feature and would
> want it re-enabled asap) you can use something like:
>=20
> cd ${jail_root}
> j_root=3D`pwd`
> cd ${jail_var_log_dir}
> j_var_log=3D`pwd`
> eval evil_doer=3D\$\{j_var_log#${j_root}\}
> [ "$evil_doer" =3D "$j_var_log" ] && exit
--> Race <--
> cp -f ${temp_log} console.log
--=20
Pawel Jakub Dawidek http://www.wheel.pl
pjd@FreeBSD.org http://www.FreeBSD.org
FreeBSD committer Am I Evil? Yes, I Am!
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