Bug#307768: exim4: check_local_user should reject system users?

[Andreas Metzler]

On 2005-05-05 Marc Sherman <msherman at projectile.ca> wrote:
> It seems to me that the check_local_user router option should fail for
> system users.  Some packages that create system users already put them
> in /etc/aliases pointing to root, but there are a number of system users
> on my machine that are not currently aliased to root.  This seems like a
> maintenance hassle, and possibly a security problem.

> I suspect that if you agree with me, this would be a debian specific
> patch, not something upstream would accept; the concept of system users
> vs. regular users seems to be a debian concept introduced in adduser.

Hello,
I am currently strongly tending to close this bug as
- unsolvable
- cost/benefit. Solving is probably going to intoduce severe problems
  for some people while only only fixing a wishlist request otherwise.

The main point is that "system user that should not receive any mail"
is very hard to detect:

UID is useless for that purpose in heterogen environments (centralized
user-managment using NIS or LDAP.) 
In  http://news.gmane.org/find-root.php?message_id=%3c443AA769.4050705%40bcgreen.com%3e
Stephen Samuel <samnospam <at> bcgreen.com> writes:
| I run a hybred Red-Hat/Debian system, (started on Red-Hat), so I 
| definitely have users in the 500-1000
| range.
| I know that Solaris systems used to start at uid=100.
| 
| In other words, dumping email just based on the UID seems like a 
| dangerous thing if you want to run in a mixed environment.

Even somehow managing to detect whether the user was generated with
adduser --system
wouldn't help, as it seems to be perfectly allowable to have
"adduser --system"-generated users receive mail (I could think of e.g.
a ~/.forward-using e-mail bot running under a dedicated UID).
http://news.gmane.org/find-root.php?message_id=%3c20060410174921.GB11258%40boogie.lpds.sztaki.hu%3e

These reasons also apply to the alternative proposal #331716
(forwarding system-user mail automatically to root).

cu andreas
-- 
The 'Galactic Cleaning' policy undertaken by Emperor Zhark is a personal
vision of the emperor's, and its inclusion in this work does not constitute
tacit approval by the author or the publisher for any such projects,
howsoever undertaken.