Date: Fri, 12 Jan 2007 18:54:39 -0800 From: James Long <list@museum.rain.com> To: freebsd-questions@freebsd.org Cc: rushani@freebsd.org Subject: Re: /dev/null in a chroot Message-ID: <20070113025439.GA63533@ns.umpquanet.com>
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> 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
>
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>
> #!/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
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