/dev/null in a chroot

[Hideyuki KURASHINA]

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 at museum.rain.com> said:

> > Date: Sun, 07 Jan 2007 20:03:40 -0400
> > From: "Marc G. Fournier" <scrappy at hub.org>
> > Subject: Re: /dev/null in a chroot
> > To: Michael Grant <mgrant at grant.org>,	FreeBSD Questions
> > 	<freebsd-questions at freebsd.org>
> > Message-ID: <8A1292FC91669855CE9C3403 at 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 at 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