Applying restrictions to anonymous ftp-ers

[Jonathan I. Kamens]

In article <1991May6.190230.10494 at cica.indiana.edu>, mr at cica.indiana.edu (Michael Regoli) writes:
|> When logging into many hosts allowing anonymous ftp access, the
|> message "Guest login ok, access restrictions apply" appears upon a
|> successful login.  However, it remains to be seen what restrictions
|> are in effect.

  The access restrictions are that your UID is the anonymous ftp UID (which,
presumably, can be prevented from accessing some files by not turning on the
world access bits and not adding the ftp user to the group the files are in),
and that your root directory has been chroot()d to the ftp home directory. 
This means that if the ftp home directory in /etc/passwd is /usr/spool/ftp,
then you can only access files and directories in /usr/spool/ftp and its
subdirectories.

  This is documented in the man page ftpd(8).

|> What measures can be applied via BSD ftpd to restrict access to
|> certain ftp commands?  More specifically, how can files in a public
|> area be "protected" (*and* still remain public) from damage by other
|> anonymous ftp-ers?  (Thankfully ftp won't allow files to "collide"
|> that have the same name.)

  Don't make the files world-writeable.  Don't make them owned by the ftp UID.

  If you want to have a drop-off location like /contrib where people can put
stuff, you should make the directory world-executable and world-writeable, but
not world-readable.  This will allow anonymous ftp contributors to put files
into it, but not to list the files in it unless they know the names of those
files.  Then, you occasionally have to scan this directory as a UID that can
read it (e.g. root or whomever owns the directory) and copy files out of it
into a world-readable directory if you want to save them.

  This has several advantages, including the fact that you know what is being
made available on your machine, so you can't get sued when people use your
machine's anonymous ftp directory as a drop-off point for illegal information
of some sort.  Or just for information that takes up many meg of disk space
that you can't spare.

-- 
Jonathan Kamens			              USnail:
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