ports/108009: scponlyc sftp support doesn't work without minimal devfs in chroot dir

[Jim Long]

>Number:         108009
>Category:       ports
>Synopsis:       scponlyc sftp support doesn't work without minimal devfs in chroot dir
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-ports-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Jan 16 18:40:25 GMT 2007
>Closed-Date:
>Last-Modified:
>Originator:     Jim Long
>Release:        6.2-PRERELEASE
>Organization:
UmpquaNet.com
>Environment:
FreeBSD t30.museum.rain.com 6.2-STABLE FreeBSD 6.2-STABLE #0: Mon Jan 15 10:32:09 PST 2007     root at t30.museum.rain.com:/usr/obj/usr/src/sys/T30  i386

>Description:
I'm finding that recently-created scponlyc chroots do not provide a sufficient environment for /usr/libexec/sftp-server to run.  The sftp client symptom is just:

$ sftp user 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.

To automatically create at boot time a devfs in the home directory of each user of scponlyc, I have chosen to put a script in /usr/local/etc/rc.d.

/usr/local/etc/rc.d/scponlyc.sh:

#!/bin/sh

ETCSHELLS="${ETCSHELLS:-/etc/shells}"
ETCPASSWD="${ETCPASSWD:-/etc/passwd}"

# script to create devfs filesystems at boot time for scponlyc
# chroot'ed users.  We will read ${ETCSHELLS} to determine
# where scponlyc is installed.  Then we'll iterate through
# each user in ${ETCPASSWD} to find users whose shell is set to
# scponlyc.  For each such user found, we will create a
# minimal devfs under ~/dev.


make_devfs() {
# $1 is the user name whose home directory needs a minimal
# devfs created.  If ~/dev exists, it will be deleted.

eval DEV="~$1/dev"
while /sbin/umount "${DEV}" 2>/dev/null; do :; done
rm -rf "${DEV}"
mkdir -p "${DEV}"
if /sbin/mount_devfs devfs "${DEV}"; then
  /sbin/devfs -m "${DEV}" rule -s 1 applyset && \
  /sbin/devfs -m "${DEV}" rule -s 2 applyset || \
    /sbin/umount "${DEV}" 2>/dev/null
fi

}


scponlyc_startup() {
# $1 is the path to the /etc/passwd file

grep "^[^#]*:.*:.*:.*:.*:.*:${SCPONLYC}$" < "$1" |
  /usr/bin/awk -F: {'print $1'} |
    while read USER; do
      make_devfs "${USER}"
    done

}


SCPONLYC=`/usr/bin/grep "/scponlyc$" ${ETCSHELLS} 2>/dev/null | /usr/bin/tail -1`

if [ "x${SCPONLYC}" = "x" ]; then
  echo scponlyc is not defined in ${ETCSHELLS} >&2
  exit 1
fi

case "$1" in
start)
        scponlyc_startup "${ETCPASSWD}"
        echo -n ' scponlyc'
        ;;
*)
        echo "Usage: `basename $0` start" >&2
        ;;
esac

exit 0

>How-To-Repeat:
Install shells/scponly with WITH_SCPONLY_CHROOT.

Run "cd /usr/local/share/examples/scponly/ && ./setup_chroot.sh"
to create an scponlyc user "test-user" and chroot homedir.

# sftp test-user at localhost
Connecting to localhost...
Password:
Connection closed


>Fix:
Install above script in /usr/local/etc/rc.d/scponlyc.sh.  Run "/usr/local/etc/rc.d/scponlyc.sh start"

# sftp test-user at localhost
Connecting to localhost...
Password:
sftp> ls
bin       dev       etc       incoming  lib       libexec   usr
sftp> quit

>Release-Note:
>Audit-Trail:
>Unformatted: