Path: utzoo!attcan!uunet!decwrl!ucbvax!CS.NIU.EDU!rickert
From: rickert@CS.NIU.EDU (Neil Rickert)
Newsgroups: comp.mail.sendmail
Subject: Re: RFC-compliant UUCP mail
Message-ID: <9007301525.AA06048@cs.niu.edu>
Date: 30 Jul 90 15:25:34 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 106

mark@DRD.Com wrote:
>   We're an MX served uucp-only site.  I note that when mail originated from
>   here arrives at some recipient, transported via the good graces of our 
>   local friendly neighborhood internet gateway, the headers look like:
>
>   From drd!DRD.Com!user  (is this the From_ referred to above?)
>   From: user@DRD.Com

 To this I replied:
>
> If you are using a standard Sun sendmail.main.cf, try using the 'smartuucp'
> mailer to forward mail to the internet gateway.  Then experiment with changing:
>  Msmartuucp, P=/usr/bin/uux, F=CmsDFMhuU, S=22, R=22, 
> to:
>  Msmartuucp, P=/usr/bin/uux, F=CmsDFMhu, S=22, R=22, 
>   In otherwords, try removing the 'U' from the end of the F= flags.
> your mail should then go out as
>  From user@DRD.com

 Unfortunately this may not work reliably.

 I suggested this because I had just implemented this scheme recently on
a UUCP node for which I provide Internet gateway services.  It worked well.
But I forgot about one piece of the puzzle which I happened to have put in
place some time ago.

 Here, specifically, is what is happening:

 If you use the 'smartuucp' mailer as originally defined, sendmail.cf formats
the addresses in domain format.  Thus the envelope address is formatted as
 'user@DRD.com'.  However, because of the 'U' mailer flag, code within the
sendmail binary converts this to:
From DRD.com!user  date and time remote from drd

 At the Internet gateway host (hereinafter known as i.g.h), the 'rmail'
converts the 'From_' line into drd!DRD.com!user, and invokes sendmail
as:
    /usr/lib/sendmail -f drd!DRD.com!user <recipient address>

 If, not, you remove the 'U' flag from the mailer, the address is formatted
as 
From user@DRD.com date and time.
Once again the receiving 'rmail' interprets this from line, and invokes
sendmail as:
    /usr/lib/sendmail -f user@DRD.com <recipient address>

 At first glance this looks to be exactly what is required.  Unfortunately,
however, most versions of 'sendmail' normally ignore the '-f' option on the
command line, unless invoked by a 'trusted user'.  This is to prevent the
forging of sender addresses.  There is one exception to this sendmail
restriction.  If the sender address contains a '!', sendmail accepts the '-f'
option, even if from a non-trusted user - UUCP mail would not work otherwise.

 The problem now, is that when the from line contains an '@' instead of a '!'
the address may go out as:  From drd@i.g.h  instead of From user@DRD.com.
It all depends on how the UUCP connection is made.
  If the UUCP connection is started by i.g.h from 'crontab' everything should
be fine, because 'uucp' is usually a Trusted user.  If the uucp connection
in initiated by 'drd', everything will be file PROVIDED that the login name
'drd' uses is a trusted user in 'sendmail.cf'.  But if the uucp connections
is initiated by, for instance, a user on i.g.h issuing the 'uucp' command,
this will not work.

  Any of the following should solve the problem:

	1.	Make sure that the outgoing UUCP mail says:
		From_DRD.com!user  date&time.
		The idea here is that there should be a bang in the
		address.  This could be managed by restoring the U flag
		and replacing uux by a shell script uux.sh which strips
		off the 'remote from drd' (with sed) and feeds its output
		to the real uux.


	2.	Create a new rewrite ruleset in sendmail.cf which converts
		all addresses to domain!user format.  Use this on the S= line
		of the mailer definition.  It probably need only consist of
		something simple like:
		R$+		$:$>22$1
		R$+		$@$>5$1

		The disadvantate is that the header line will also go out
		as:
		From: DRD.com!user
		This is probably not serious, for i.g.h will probably convert
		that into user@DRD.com.

	3.	Make sure that all UUCP calls are initiated from 'drd'
		and that the login name used is on the trusted user list
		at i.g.h.

	4.	Modify 'rmail' on i.g.h. This is the method I am currently
		using.  My 'rmail', which came with the sendmail/IDA package,
		is suid root, and sets its real uid to 0 before invoking
		sendmail.  This means that it is always trusted.

		I also set 'rmail' to be in group 'daemon' and executable only
		by 'user' or 'group'.  Uucp usually runs sgid daemon, so can
		execute rmail, but typical users cannot.  Of course a user
		who wants to forge mail can still do it by using '!' in the
		from address.

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  Neil W. Rickert, Computer Sci Dept, Northern Illinois U., DeKalb IL 60115
  InterNet, unix: rickert@cs.niu.edu              Bitnet, VM: T90NWR1@NIUCS
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