How to setup WU-FTPD Guest Accounts

• LINUX:
• SOLARIS:
• SUN 4.1.x:
• BSDI:
• IRIX (5.3, 6.x):
• AIX:

Introduction

1. anonymous FTP
2. real FTP
3. guest FTP

Real FTP is when someone logs in with a real username and password and has access to the entire disk structure. This form of access can be extremely dangerous to system security and should be avoided unless absolutely necessary and well controlled.

Guest FTP is a form of real FTP; one logs in with a real user name and password, but the user is chroot'ed to his home directory and cannot escape from it. This is much safer, and it is a useful way for remote clients to maintain their Web accounts.

If you want to learn more about 'chroot', the following two commands should help, as should any good Unix text.

man chroot

This howto will describe in detail the steps necessary to set up a guest FTP account. It does not describe anonymous or real FTP setup, though the procedures for setting up an operational 'ls' command will apply equally to anonymous FTP because of the chroot'ed nature of anonymous FTP.

Working Example

(Yes, there is some droll humor here for the French speakers...)

1. Do the /etc hacks

Create Mort's entry in /etc/passwd and /etc/group. Do so manually, or use adduser or whatever your Unix supports. If you use adduser, you will probably have to make manual modifications to get the /./ information in the home path.

There are also entries to make in /etc/ftpaccess.

/etc/passwd:

mort:*:403:400:Mortimer Snerd:/home/web/mort/./:/etc/ftponly
                                            ^^^

The /./ sequence determines where the chroot() is done to. If you want the chroot() done to the web directory and a chdir() to mort, it would look like this:

mort:*:403:400:Mortimer Snerd:/home/web/./mort/:/etc/ftponly
                                       ^^^

--------> (make sure "/etc/ftponly" is in /etc/shells.)

/etc/group:

client::400:mort

Set Mort's password as you wish, or better yet use S/KEY.

If you are using the Beta version of ftpd (HIGHLY RECOMMENDED) that Stan Barber has put together, you must do one of two things to properly use /etc/ftpaccess:

1. compile the source to use /etc/ftpaccess by default (comes turned off); hack the source to set use_accessfile = 1;

   OR

2. run the daemon with the -a option.

/etc/ftpaccess:
class   local   real,guest,anonymous ......
...                  ^^^^^
...                    +----------- define 'guest' in the proper classes;
...                                 this is site dependent.
...
...
delete     no   anonymous,guest               # delete permission?
overwrite  no   anonymous,guest               # overwrite permission?
rename     no   anonymous,guest               # rename permission?
chmod      no   anonymous,guest               # chmod permission?
umask      no   anonymous,guest               # umask permission?
...                       ^^^^^
...                         +------ decide if guest should be in this 
...                                 permission list; this is site dependent.
...
...
path-filter  guest      /etc/pathmsg  ^[-A-Za-z0-9_\.]*$  ^\.  ^-
...
guestgroup client
...

2. Create Mort's home directory and set its ownership and protections

• mkdir /home/web/mort

• chown mort.client /home/web/mort

• chmod 755 /home/web/mort

3. Build the directory structure under Mort's account.

• cd /home/web/mort

• mkdir etc bin [dev lib] (dev and lib are optional and are OS dependent.)

• chown root.daemon etc bin

• chmod 111 etc bin

4. Build the contents of the ~/bin directory.

USE STATICALLY LINKED COPIES OF ALL UTILITIES IF POSSIBLE -- YOUR LIFE (AND EVERYONE ELSE'S ON wu-ftpd@wugate.wustl.edu) WILL BE SIMPLER.

• cp /.../bin/ls bin
• chown root.bin bin/ls
• chmod 111 bin/ls

Optional for on the fly compression and tar:

• cp /.../bin/gzip bin
• cp /.../bin/tar bin
• chown root.bin bin/gzip
• chown root.bin bin/tar
• chmod 111 bin/gzip
• chmod 111 bin/tar

If the utilities are not static, create the necessary devices in ~/dev and copy the necessary libraries into ~/lib. Check the man page for ftpd that comes with your system; it may be of help.

REGARDING HARD AND SOFT/SYMBOLIC LINKS:

The chroot() obviates the use of soft links in this case. However, it it is possible to make these hard links back to the master copy of the utilities rather than copies. This can save some disk space if that is a concern.

5. Build the contents of the ~/etc directory.

• Edit "passwd" to contain the following:

  root:*:0:0::/:/etc/ftponly
  mort:*:403:400::/home/web/mort/./:/etc/ftponly
  

• Edit "group" to contain the following:

  root::0:root
  client::400:mort
  

• chown root.daemon passwd group

• chmod 444 passwd group

6. Add some extra security touches

• cd /home/web/mort
• touch .rhosts .forward
• chown root.root .rhosts .forward
• chmod 400 .rhosts .forward

You should now be the proud owner of a working guest group FTP login. Connect to the machine via FTP and login as "mort". You should end up in Mort's account with a current directory of "/".

If not, go over it carefully again, as there is a lot of detail here. If you still can't get it to work, yell for help on wu-ftpd@wugate.wustl.edu.

OS DEPENDENCIES / QUIRKS

LINUX:

Linux does not need a ~/dev dir. It does need the ~/lib dir if the utilities in ~/bin are dynamically linked.

Use the 'ldd' command to find out what libraries are necessary for a given dynamically linked utility.

SOLARIS:

Solaris can't handle SETPROCTITLE, so turn the compile time option off.

(The following was culled from a post by Tom Leach to the wu-ftpd list.)

>For people who are having problems with ls -al and dir on solaris 2.x
>systems, you might try the following to find out what's missing...

>truss -f chroot ~ftp /bin/ls

>This will run the ls command in the same chroot'd environment that
>anonymous FTP runs in. The truss will show you what
>files/libraries/devices are accessed and where the ls is looking for them.

>Tom Leach
>leach@oce.orst.edu

SUN 4.1.x:

Create a ~dev/zero and ~dev/tcp device for the FTP directory as follows. Run the following 'ls' command, then create the devices in the ~/dev directory with the 'mknod' command, using the major and minor numbers from the 'ls' results (thanks to Jim Davis <jdavis@cs.arizona.edu>).

ls -lL /dev/zero /dev/tcp

cd dev
mknod zero c <major> <minor>
mknod tcp c <major> <minor>
cd ..
chmod 555 dev

You may also wish to use the following method to create the device, per Ian Willis <ianw@sco.com>; repeat this command for each device (zero, tcp, etc.).

find /dev/zero -print | cpio -pd ~ftp

Also, you probably need the following shared libraries:

• ~lib/ld.so
• ~lib/libc.so
• ~lib/libdl.so

BSDI:

Set 555 protections on the ~ftp/shlib and its contents if shared libraries are used.

From Darci Chapman (minerva@phix.com):

The following directories and files need to be created in whatever directory/ies are being chrooted to (~ftp for anon ftp or for whatever directory guest users are chrooted):

dr-xr-xr-x root/wheel        0 Nov  3 01:43 1995 bin/
-r-xr-xr-x root/wheel    12288 Nov  3 01:43 1995 bin/compress
-r-xr-xr-x root/wheel    45056 Nov  3 01:43 1995 bin/gzip
-r-xr-xr-x root/wheel    12288 Nov  3 01:43 1995 bin/ls
-r-xr-xr-x root/wheel    65536 Nov  3 01:43 1995 bin/pax
dr-xr-xr-x root/wheel        0 Nov  3 01:43 1995 etc/
-r--r--r-- root/wheel      793 Nov  3 01:43 1995 etc/group
-r--r--r-- root/wheel      817 Nov  3 01:43 1995 etc/localtime
-r--r--r-- root/wheel    40960 Nov  3 01:43 1995 etc/pwd.db
dr-xr-xr-x root/wheel        0 Feb  3 12:34 1995 pub/
dr-xr-xr-x root/wheel        0 Nov  3 01:43 1995 shlib/
-r-xr-xr-x root/wheel   298407 Nov  3 01:43 1995 shlib/libc_s.2.0

IRIX (5.3, 6.x):

From Frans Stekelenburg <gjs@knmi.nl>:

(as in SUN 4.1.x, but without /dev/tcp)

Create a ~dev/zero and ~dev/tcp device for the FTP directory as follows. (tip: search on 'dev/zero' in your IRIX systems' Online Books.) Run the following 'ls' command, then create the devices in the ~/dev directory with the 'mknod' command, using the major and minor numbers from the 'ls' results (thanks to Jim Davis <jdavis@cs.arizona.edu>).

ls -lL /dev/zero /dev/tcp

cd dev
mknod zero c <major> <minor>
cd ..
chmod 555 dev

You may also wish to use the following method to create the device, per Ian Willis <ianw@sco.com>; repeat this command for each device (zero, etc.).

find /dev/zero -print | cpio -pd ~ftp

Also, you probably need the following shared libraries:

• ~lib/rld
• ~lib/libc.so.1
• (found in /lib)

Also read the manpages on FTPD, or look in the IRIX Insight Library (Online Books) in the book/chapter "IRIX Admin: Networking and Mail" for the paragraph 'How to Set Up a Proper Anonymous FTP Account' (search helps:-)) on your IRIX system.

AIX:

Per Chuque Berry <chuque@ns2.tiba.net> and Joseph Matusiewicz <Joseph.Matusiewicz@noaa.gov>, AIX needs the following files for the external ls to work:

• ~lib/libc.a
• ~lib/libcurses.a (???)

Additionally:

• For extra tips on security see Christopher Klaus's FAQ:

  http://www.iss.net/vd/anonftp.html

• If you run across some special trick required to get guest access to run on your OS, or some security cleanup, please let me know and I will update the master of this document.

• Don't contact me individually for help. Go through the wu-ftpd list for that and I will see the post there.

Michael Brennen
mbrennen@fni.com