From: Matt Carpenter <mcarpent@Dusk.obscure.net>
Date: Sun, 14 Jul 1996 21:59:55 +0800
To: hfinney@shell.portal.com
Subject: Re:  Execution of signed scripts received by e-mail
Message-ID: <199607141042.FAA01300@Dusk.obscure.net>
MIME-Version: 1.0
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Hal <hfinney@shell.portal.com> writes:
> 
> That sounds very impressive!  The one problem I've run into with mail
> filtering software is that each message asynchronously spawns a separate
> filter process.  This can cause some conflicts with accessing disk files.
> I haven't used procmail so I don't know if it has this problem.  But if
> so you may need to be careful if there are any cases where two processes
> could be accessing the same disk files.  For example, what if two copies
> of an identical email message arrive at almost the same time, would your
> dup detection work.

If I am reading the procmail docs correctly, then the following recipe
should create a lockfile called 'emscrypt.lock' which will prevent more than
one instance of the script from being run at a time

:0:emscrypt
^ Subject.*SQUEAMISH OSSIFRAGE
|/PATH/emscrypt

I agree it would be better if emscrypt used its own locks on the timestamp
files.  However, it is my understanding (someone please correct me if I am
wrong) that there is no simple way to provide file locking in Perl that is
portable across the various flavours of Unix (see the descriptions of the
fcntl and flock functions on p. 144-145 of the Camel book).  So I haven't
tried to implement locking from within emscrypt yet.  Of course, if these
functions are available on the majority of machines (anyone?) then I should
probably use them.

> The other issue is the possibility of mail arriving out of order.  Looking
> for increasing timestamps may cause spurious rejection of some messages.
> On the other hand this is a difficult problem to handle in general so
> probably the current solution is OK.

Yeah, I though about that too.  It can be somewhat alleviated by
batching the individually signed scripts into a single mail message, if 
you know you are going to be submitting several scripts close together 
in time.

Any other ideas?

> 
> Hal
> 

Thanks for the feedback.

- --Matt

- --
mcarpent@mailhost.tcs.tulane.edu

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