Date: Mon, 15 Jan 2007 21:12:24 +0900 (JST) From: Hideyuki KURASHINA <rushani@FreeBSD.org> To: list@museum.rain.com Cc: freebsd-questions@freebsd.org Subject: Re: /dev/null in a chroot Message-ID: <20070115.211224.41626423.rushani@FreeBSD.org> In-Reply-To: <20070113025439.GA63533@ns.umpquanet.com> References: <20070113025439.GA63533@ns.umpquanet.com>
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Thank you for describing the issue.
Could you please file the PR not to miss this useful suggestion?
Regards,
>>> On Fri, 12 Jan 2007 18:54:39 -0800, James Long <list@museum.rain.com> said:
> > Date: Sun, 07 Jan 2007 20:03:40 -0400
> > From: "Marc G. Fournier" <scrappy@hub.org>
> > Subject: Re: /dev/null in a chroot
> > To: Michael Grant <mgrant@grant.org>, FreeBSD Questions
> > <freebsd-questions@freebsd.org>
> > Message-ID: <8A1292FC91669855CE9C3403@ganymede.hub.org>
> > Content-Type: text/plain; charset=us-ascii
> >
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> >
> > #!/bin/sh
> > /sbin/devfs -m $1 rule apply hide
> > /sbin/devfs -m $1 rule apply path null unhide
> >
> > where $1 == the dev directory you mount within the chroot environment ...
>
> This issue is currently biting users of /usr/ports/security/scponly
> also, I believe.
>
> I'm finding that recently-created scponlyc chroots do not permit sftp
> login, although they do allow ftp login. The client symptom is just:
>
> $ sftp newuser@www
> Connecting to www...
> Password:
> Connection closed
> $
>
> The cause appears to be that recent versions of
> /usr/libexec/sftp-server will complain about of lack of access to
> /dev/null and exit, resulting in the closed connection witnessed by
> the remote client.
>
> The solution appears to be to create a devfs in the scponlyc chroot.
>
> This is a little disappointing, as scponlyc used to be delightfully
> lightweight and low-maintenance. At this point, my understanding is
> that the devfs requirement means that now I must run a script at boot
> time that iterates through a list of chroot'ed users and create dev
> nodes within each jail. scponlyc jails were previously a
> set-and-forget type of setup.
>
> What is the proper mechanism for setting up an arbitrary number of
> scponlyc chroots at boot time? /usr/share/examples/etc/devfs.conf
> doesn't show an example of how to apply these rules to a non-default
> dev path. I have chosen to put a script in /usr/local/etc/rc.d.
>
> In case other scponly users are reading this in the archives, the
> manual method that works for me with 6.2-PRE and scponly-4.6_1 is:
>
> # cd ~user
> # mkdir -p dev
> # mount_devfs devfs dev
> # devfs -m dev rule -s 1 applyset
> # devfs -m dev rule -s 2 applyset
>
> One then sees:
>
> # ls -l dev
> total 0
> crw-rw-rw- 1 root wheel 0, 6 Jan 12 17:15 null
> crw-rw-rw- 1 root wheel 0, 12 Jan 10 07:57 random
> lrwxr-xr-x 1 root wheel 6 Jan 12 16:54 urandom@ -> random
> crw-rw-rw- 1 root wheel 0, 7 Jan 10 15:57 zero
>
> which is more than enough to appease /usr/libexec/sftp-server.
>
> chroots created some months ago contain lib versions with numbers
> typically one less, such as ./usr/lib/libssh.so.2 in the older
> chroot, versus ./usr/lib/libssh.so.3 in the newer. The older
> scponly chroots do net require devfs nodes! I suspect they will
> eventually break though, given enough time.
>
> Given that scponlyc provides a setup_chroot.sh script that provides
> hooks for OS-specific chroot setup steps, would it help the port
> maintainer to provide the shell script below? I have it installed
> in /usr/local/etc/rc.d/scponlyc.sh.
>
>
> Jim
>
>
>
> #!/bin/sh
>
> # script to create devfs filesystems at boot time for scponlyc
> # chroot'ed users. We will read /etc/shells to determine
> # where scponlyc is installed. Then we'll iterate through
> # each user in /etc/passwd to find users whose shell is set to
> # scponlyc. For each such user found, we will create a
> # minimal devfs under ~/dev.
>
>
>
> SCPONLYC=$(/usr/bin/grep "/scponlyc$" /etc/shells 2>/dev/null | /usr/bin/tail -1)
>
>
> make_devfs() {
> # $1 is the user name whose home directory needs a minimal
> # devfs created. If ~/dev is not a directory, it will be
> # deleted and replaced with a directory.
>
> eval DEV="~$1/dev"
> while /sbin/umount ${DEV} 2>/dev/null; do :; done
> [ -h "${DEV}" ] && rm "${DEV}"
> [ -f "${DEV}" ] && rm "${DEV}"
> mkdir -p "${DEV}"
> if /sbin/mount_devfs devfs "${DEV}"; then
> /sbin/devfs -m "${DEV}" rule -s 1 applyset || /sbin/umount ${DEV} 2>/dev/null
> /sbin/devfs -m "${DEV}" rule -s 2 applyset || /sbin/umount ${DEV} 2>/dev/null
> fi
>
> }
>
>
> scponly_startup() {
> # $1 is the path to the /etc/passwd file
>
> if [ "x${SCPONLYC}" = "x" ]; then
> echo scponlyc is not defined in /etc/shells >&2
> exit 1
> fi
>
> /usr/bin/grep -v "^[ ]*#" "$1" |
> /usr/bin/awk -F: {'print $1 " " $7'} |
> while read USER SHELL; do
> if [ "x${SHELL}" = "x${SCPONLYC}" ]; then
> make_devfs "${USER}"
> fi
> done
>
> }
>
>
> case "$1" in
> start)
> scponly_startup "/etc/passwd"
> echo -n ' scponlyc'
> ;;
> *)
> echo "Usage: `basename $0` start" >&2
> ;;
> esac
>
> exit 0
-- rushani
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