Re: segfault in ftpd

From: Garrett Wollman (wollman@lcs.mit.edu)
Date: 04/24/02 

Date: Tue, 23 Apr 2002 23:10:48 -0400 (EDT)
From: Garrett Wollman <wollman@lcs.mit.edu>
To: Mikko Tyolajarvi <mikko@dynas.se>

<<On Tue, 23 Apr 2002 19:53:53 -0700 (PDT), Mikko Tyolajarvi <mikko@dynas.se> said:

> makes it such a security problem in the first place -- how often do
> you _really_ need to change user in the middle of an ftp session?
> It should just switch uid and be done with it, IMHO).

Unfortunately, the people who designed the FTP protocol did not
consider the notion of `privileged ports'. As a result, an
active-mode FTP connection is required to originate from
<control.channel.ip.address, 20>, which means that for every
active-mode FTP operation, the FTP server must be able to bind to a
privileged port.

An implementation of capabilities would obviate this problem: ftp
could change its context entirely to that of the client, except
leaving the `can bind low ports' bit on, and still be able to
accomplish what it needs to do.

-GAWollman

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