installation of sendmail milters, security questions

Matthew Seaman m.seaman at
Sun Oct 17 03:39:31 PDT 2004

On Sat, Oct 16, 2004 at 07:56:45PM -0600, Gary Aitken wrote:

> Trying to install milter-greylist.
> After configuring sendmail, and without the milter-greylist daemon
> running, maillog contains messages of the type:
> sm-mta[59533]: i9H12H4P059533: Milter (greylist): local socket name 
> /var/milter-greylist/milter-greylist.sock unsafe
> From what I've been able to dig up, this is because sendmail thinks
> it's unsafe to read/write that socket.

No, this is sendmail's convoluted way of telling you that
milter-greylist isn't actually running, and so it would be unsafe
(ie. might result in lost e-mail) if it was to attempt to communicate
via the socket with that non-existent process.  It doesn't have
anything to do with the ownership/permissions of either the
milter-greylist socket, or the milter-greylist process itself.

The answer is just to start up the milter-greylist process.

> Upon checking, I discovered /var/milter-greylist was owned by smmsp,
> so I changed it to root.  Unfortunately, that didn't solve the
> problem.

Um... don't do that.  Leave the permissions as they were when the port
was installed.  The various parts of the mail system are deliberately
configured to run as *non root* for security reasons: essentially, if
someone can take over the process by eg. a buffer overflow attack, all
they get is a process with ordinary user credentials, so limiting the
amount of damage they can do.  /var/milter-greylist has to be writable
by the UID milter-greylist runs as, and the best way of doing that is
to give that UID ownership of the directory.



Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
PGP:         Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK
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